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Showing papers on "Leading edge published in 2008"


Patent
20 Jun 2008
TL;DR: In this article, an air mixing arrangement where a primary fluid is introduced through an opening in a wall to be mixed with a secondary fluid flowing along the wall surface, the opening is airfoil shaped with its leading edge being orientated at an attack angle with respect to the secondary fluid flow stream.
Abstract: In an air mixing arrangement wherein a primary fluid is introduced through an opening in a wall to be mixed with a secondary fluid flowing along the wall surface, the opening is airfoil shaped with its leading edge being orientated at an attack angle with respect to the secondary fluid flow stream so as to thereby enhance the penetration and dispersion of the primary fluid stream into the secondary fluid stream. The airfoil shaped opening is selectively positioned such that its angle of attack provides the desired lift to optimize the mixing of the two streams for the particular application. In one embodiment, a collar is provided around the opening to prevent the secondary fluid from contacting the surface of the wall during certain conditions of operation. Multiple openings maybe used such as the combination of a larger airfoil shaped opening with a smaller airfoil shaped opened positioned downstream thereof, or a round shaped opening placed upstream of an airfoil shaped opening. Pairs of openings and associated collars maybe placed in symmetric relationship so as to promote mixing in particular applications, and nozzles maybe placed on the inner side of wall to enhance the flow characteristics of the primary fluid.

352 citations


Journal ArticleDOI
TL;DR: An aerodynamic model is developed which explains the observed increase in stall angle and finds that stall delay is insensitive to the wavelength of the bumps, in accordance with experimental observations.
Abstract: Wind tunnel experiments have shown that bumps on the leading edge of model humpback whale flippers cause them to "stall" (i.e., lose lift dramatically) more gradually and at a higher angle of attack. Here we develop an aerodynamic model which explains the observed increase in stall angle. The model predicts that as the amplitude of the bumps is increased, the lift curve flattens out, leading to potentially desirable control properties. We find that stall delay is insensitive to the wavelength of the bumps, in accordance with experimental observations.

195 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a new formulation of the motion of a flexible body with a vortex-sheet wake and use it to study propulsive forces generated by the flexible body pitched periodically at the leading edge in the small-amplitude regime.
Abstract: We present a new formulation of the motion of a flexible body with a vortex-sheet wake and use it to study propulsive forces generated by a flexible body pitched periodically at the leading edge in the small-amplitude regime. We find that the thrust power generated by the body has a series of resonant peaks with respect to rigidity, the highest of which corresponds to a body flexed upwards at the trailing edge in an approximately one-quarter-wavelength mode of deflection. The optimal efficiency approaches 1 as rigidity becomes small and decreases to 30–50 % (depending on pitch frequency) as rigidity becomes large. The optimal rigidity for thrust power increases from approximately 60 for large pitching frequency to ∞ for pitching frequency 0.27. Subsequent peaks in response have power-law scalings with respect to rigidity and correspond to higher-wavenumber modes of the body. We derive the power-law scalings by analysing the fin as a damped resonant system. In the limit of small driving frequency, solutions are self-similar at the leading edge. In the limit of large driving frequency, we find that the distribution of resonant rigidities ∼k −5 , corresponding to fin shapes with wavenumber k. The input power and output power are proportional to rigidity (for small-to-moderate rigidity) and to pitching frequency (for moderateto-large frequency). We compare these results with the range of rigidity and flapping frequency for the hawkmoth forewing and the bluegill sunfish pectoral fin.

164 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined the voltage requirements for the plasma actuators to reattach the flow at the leading edge of airfoils at poststall angles of attack for a range of flow parameters in order to establish scaling between laboratory and full flight conditions.
Abstract: We present experimental results to yield insight into the scalability and control effectiveness of single-dielectricbarrier-discharge plasma actuators for leading-edge separation control on airfoils. The parameters investigated are chord Reynolds number, Mach number, leading-edge radius, actuator amplitude, and unsteady frequency. This includes chord Reynolds numbers up to 1:0 � 106 and a maximum freestream speed of 60 m=s corresponding to a Mach number of 0.176. The main objective of this work is to examine the voltage requirements for the plasma actuators to reattach the flow at the leading edge of airfoils at poststall angles of attack for a range of flow parameters in order to establish scaling between laboratory and full-flight conditions. For the full range of conditions, an optimum unsteady actuator frequency f is found to minimize the actuator voltage needed to reattach the flow, such that F� � fLsep=U1 � 1. At the optimum frequencies, the minimum voltage required to reattach the flow is weakly dependent on chord Reynolds number and strongly dependent on the poststall angle of attack and leading-edge radius. The results indicate that the voltage required to reattach the flow scales as the square of the leading-edge radius.

136 citations


Journal ArticleDOI
TL;DR: In this article, a 0.2m NACA 63 415 blade profile in the refrigerated wind tunnel of the Anti-icing Materials International Laboratory (AMIL) was measured, as well as the lift and drag forces of the iced profiles.
Abstract: The wind energy market is in full growth in Quebec but technical difficulties due to cold climate conditions have occurred for most of the existing projects. Thus, icing simulations were carried out on a 0.2 m NACA 63 415 blade profile in the refrigerated wind tunnel of the Anti-icing Materials International Laboratory (AMIL). The shapes and masses of the ice deposits were measured, as well as the lift and drag forces of the iced profiles. Scaling was carried out based on the 1.8 MW–Vestas V80 wind turbine technical data, for three different radial positions and two in-fog icing conditions measured at the Murdochville wind farm in the Gaspe Peninsula. For both icing events, the mass of ice accumulated on the blade profile increased with an increase in the radial position. In wet regime testing (first icing event), glaze formed mostly near the leading edge and on the pressure side. It also accumulated by run-off on the trailing edge of the outer half of the blade. In dry-regime testing (second icing event), rime mostly accreted on the leading edge and formed horns. For both icing events, when glaze or rime accreted on the blade profile, lift decreased and drag increased. A load calculation using the blade element theory shows that drag force on the entire blade becomes too large compared to lift, leading to a negative torque and the stop of the wind turbine. Torque reduction is more significant on the outer third of the blade. Setting up a de-icing system only on the outer part of the blade would enable significant decrease of heating energy costs. Copyright © 2007 John Wiley & Sons, Ltd.

122 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of crossflow on the dynamics, entrainment and mixing characteristics of vortex rings issuing from a circular nozzle was studied, and three distinct regimes exist, depending on the velocity ratio (ratio of the average nozzle exit velocity to free-stream crossflow velocity) and stroke ratio.
Abstract: Direct numerical simulation is used to study the effect of crossflow on the dynamics, entrainment and mixing characteristics of vortex rings issuing from a circular nozzle. Three distinct regimes exist, depending on the velocity ratio (ratio of the average nozzle exit velocity to free-stream crossflow velocity) and stroke ratio (ratio of stroke length to nozzle exit diameter). Coherent vortex rings are not obtained at velocity ratios below approximately 2. At these low velocity ratios, the vorticity in the crossflow boundary layer inhibits roll-up of the nozzle boundary layer at the leading edge. As a result, a hairpin vortex forms instead of a vortex ring. For large stroke ratios and velocity ratio below 2, a series of hairpin vortices is shed downstream. The shedding is quite periodic for very low Reynolds numbers. For velocity ratios above 2, two regimes are obtained depending upon the stroke ratio. Lower stroke ratios yield a coherent asymmetric vortex ring, while higher stroke ratios yield an asymmetric vortex ring accompanied by a trailing column of vorticity. These two regimes are separated by a transition stroke ratio whose value decreases with decreasing velocity ratio. For very high values of the velocity ratio, the transition stroke ratio approaches the ‘formation number’. In the absence of trailing vorticity, the vortex ring tilts towards the upstream direction, while the presence of a trailing column causes it to tilt downstream. This behaviour is explained. In the absence of crossflow, the trailing column is not very effective at entrainment, and is best avoided for optimal mixing and entrainment. However, in the presence of crossflow, the trailing column is found to contribute significantly to the overall mixing and entrainment. The trailing column interacts with the crossflow to generate a region of high pressure downstream of the nozzle that drives crossflow fluid towards the vortex ring. There is an optimal length of the trailing column for maximum downstream entrainment. A classification map which categorizes the different regimes is developed.

119 citations


Journal ArticleDOI
TL;DR: In this paper, a three-dimensional twisted hydrofoil with an attached cavitaty closely related to propellers was observed with a high-speed camera at the University of Delft Cavitation Tunnel.
Abstract: A three-dimensional twisted hydrofoil with an attached cavitaty closely related to propellers was observed with a high-speed camera at the University of Delft Cavitation Tunnel. Reentrant flow coming from the sides of the cavity aimed at the center plane—termed side-entrant flow—collided in the closure region of the cavity, pinching off a part of the sheet resulting in a periodic shedding. The collapse of the remainder of the sheet appears to be a mixing layer at the location of the colliding reentrant flows. Collision of side-entrant jets in the closure region of a cavity is identified as a second shedding mechanism, in addition to reentrant flow impinging the sheet interface at the leading edge.

103 citations


Journal ArticleDOI
TL;DR: The result shows that the LEV system is a collection of four vortical elements: one primary vortex and three minor vortices, instead of a single conical or tube-like vortex as reported or hypothesized in previous studies.
Abstract: SUMMARY Following the identification and confirmation of the substructures of the leading-edge vortex (LEV) system on flapping wings, it is apparent that the actual LEV structures could be more complex than had been estimated in previous investigations. In this experimental study, we reveal for the first time the detailed three-dimensional (3-D) flow structures and evolution of the LEVs on a flapping wing in the hovering condition at high Reynolds number ( Re =1624). This was accomplished by utilizing an electromechanical model dragonfly wing flapping in a water tank (mid-stroke angle of attack=60°) and applying phase-lock based multi-slice digital stereoscopic particle image velocimetry (DSPIV) to measure the target flow fields at three typical stroke phases: at 0.125 T ( T =stroke period), when the wing was accelerating; at 0.25 T , when the wing had maximum speed; and at 0.375 T , when the wing was decelerating. The result shows that the LEV system is a collection of four vortical elements: one primary vortex and three minor vortices, instead of a single conical or tube-like vortex as reported or hypothesized in previous studies. These vortical elements are highly time-dependent in structure and show distinct `stay properties9 at different spanwise sections. The spanwise flows are also time-dependent, not only in the velocity magnitude but also in direction.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of both the FST length scale and the disturbance behavior near the plate leading edge on the details of bypass transition farther downstream were investigated. But the authors focused on the effect of the length scale on the initial ingestion of FST into the boundary layer.
Abstract: Direct numerical simulations (DNS) of bypass transition due to high-amplitude free-stream turbulence (FST) are carried out for a flat-plate boundary layer. The computational domain begins upstream of the plate leading edge and extends into the fully turbulent region. Thus, there is no ad hoc treatment to account for the initial ingestion of FST into the laminar boundary layer. We study the effects of both the FST length scale and the disturbance behaviour near the plate leading edge on the details of bypass transition farther downstream. In one set of simulations, the FST parameters are chosen to match the ERCOFTAC benchmark case T3B. The inferred FST integral length scale L 11 is significantly larger (R L = UL 11 /ν =6580) than that employed in previous simulations of bypass transition (R L ≃1000). An additional set of simulations was performed at R L = 1081 to compare the transition behaviour in the T3B case with that of a smaller value of FST length scale. The FST length scale is found to have a profound impact on the mechanism of transition. While streamwise streaks (Klebanoff modes) are observed at both values of the FST length scale, they appear to have clear dynamical significance only at the smaller value of R L , where transition is concomitant with streak breakdown. For the T3B case, turbulent spots form upstream of the region where streaks could be detected. Spot precursors are traced to quasi-periodic spanwise structures, first observed as short wavepackets in the wall-normal velocity component inside the boundary layer. These structures are reoriented to become horseshoe vortices, which break down into young turbulent spots. Two of the four spots examined for this case had a downstream-pointing shape, similar to those found in experimental studies of transitional boundary layers. Additionally, our simulations indicate the importance of leading-edge receptivity for the onset of transition. Specifically, higher fluctuations of the vertical velocity at the leading edge of the plate result in higher levels of streamwise Reynolds stress inside the developing boundary layer, facilitating breakdown to turbulence.

95 citations


Dissertation
01 Jan 2008
TL;DR: Techet et al. as mentioned in this paper investigated the hydrodynamic effects of biologically-inspired leading-edge tubercles on the performance of three-dimensional hydrofoils based on the pectoral flippers of the Humpback Whale (novangilae megaptera).
Abstract: This thesis investigates the hydrodynamic effects of biologically-inspired leading-edge tubercles. Two complementary studies examine the performance of three-dimensional hydrofoils based on the pectoral flippers of the Humpback Whale (novangilae megaptera). The first study uses a static foil, with application to conventional control surfaces– such as rudders or dive planes–found on marine vehicles. The second study uses a dynamic foil, with application to flapping foil propulsion. The lift and drag characteristics of foils with and without tubercles are compared using force measurements from experiments conducted in a water tunnel at four Reynolds numbers between 4.4 × 10 and 1.2 × 10. Results from these experiments indicate the foils stall from the trailing edge in the range of Reynolds numbers tested. Stall was delayed on the foil with tubercles; maximum lift was reduced in all cases but the highest Re. PIV flow visualization at Re = 8.9 × 10 4 showed flow separation at the trailing edge of both foils as attack angle was increased, confirming that the foils were in trailing edge stall. Surface normal vorticity in ensemble averaged flow fields showed distinct pairs of opposite sign vortical structures being generated by the tubercles, providing some insight into the fluid dynamic mechanism that leads to changes in the performance of a foil with tubercles. Tubercles were used on a flapping foil for the first time. Mean thrust coefficient, CT , power coefficient, CP , and efficiency, η, were measured over a wide parametric space. The maximum thrust coefficient and efficiency measured using the smooth control foil were CT = 3.511 and η = 0.678. The maxima using the tubercled test foil were CT = 3.366 and η = 0.663. In general, the foil with tubercles performed worse than the control, and this performance deficit grew with increased loading. These results suggest that the vortical structures generated by the tubercles interfere with the thrust wake generated by flapping, ultimately degrading performance. Thesis Supervisor: Alexandra H. Techet Title: Associate Professor of Mechanical and Ocean Engineering

92 citations


Journal ArticleDOI
TL;DR: In this article, a two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out.
Abstract: Two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out. Numerical data obtained for fast and slow acoustic waves of zero angle of incidence are consistent with the asymptotic theory. Numerical experiments with acoustic waves of non-zero angles of incidence reveal new features of the disturbance field near the plate leading edge. The shock wave, which is formed near the leading edge owing to viscous–inviscid interaction, produces a profound effect on the acoustic near field and excitation of boundary-layer modes. DNS of the porous coating effect on stability and receptivity of the hypersonic boundary layer is carried out. A porous coating of regular porosity (equally spaced cylindrical blind micro-holes) effectively diminishes the second-mode growth rate in accordance with the predictions of linear stability theory, while weakly affecting acoustic waves. The coating end effects, associated with junctures between solid and porous surfaces, are investigated.

Journal ArticleDOI
TL;DR: In this paper, the aerodynamics of a Gurney-flap-equipped airfoil have been explored by means of low-speed wind-tunnel experiments performed at a chord Reynolds number of 1:0 10.
Abstract: The aerodynamics of a Gurney-flap-equipped airfoil has been explored by means of low-speed wind-tunnel experiments performed at a chord Reynolds number of 1:0 10. Various chordwise locations and sizes of Gurney flaps were tested. Surface-pressure distributions and the wake momentum deficit were measured and used to determine lift, pitching moment, and drag. Compared with the clean airfoil, the measured maximum lift coefficient can be increased by nearly 30%with these simple devices. The amount of lift increase has a nearly linear dependency on the chordwise location and size of the Gurney flap. Minimum drag is primarily affected by the flap size and, to a lesser extent, by the chordwise location. The Gurney flap increases in maximum lift are obtained by increasing the lower-surface pressures over the aft part of the airfoil. At the same time, themagnitude of pressure peak on the upper surface near the leading edge is reduced such that the upper-surface pressures over themiddle parts of the airfoil are reduced and the separation point is moved aft by the reduced pressure-recovery gradients. As expected, this increases the aft loading and results in an increased nose-down pitchingmoment. As the angle of attack is decreased, the influence of a Gurney flap extending from the lower surface likewise decreases as the flap is increasingly immersed in the thickening boundary layer. A Gurney flap mounted to the upper surface behaves in the opposite way: increasing the negative lift at low angles of attack and having less and less influence as the angle of attack is increased. AlthoughGurney flaps result in significantly higher drags for airfoils with extensive runs of laminar flow, this disadvantage disappears as the amount of turbulent boundary-layer flow increases, as is the case with fixed transition near the leading edge of the airfoil.

Journal ArticleDOI
TL;DR: In this article, active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations.
Abstract: Active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations. On the standard configuration, stall commenced inboard, but with sweep the wing stalled initially near the tip. On both configurations, leading-edge perturbations increased CL,max and post stall lift, both with and without deflected flaps. Without sweep, the effect of control was approximately uniform across the wing span but remained effective to high angles of attack near the tip; when sweep was introduced a significant effect was noted inboard, but this effect degraded along the span and produced virtually no meaningful lift enhancement near the tip, irrespective of the tip configuration. In the former case, control strengthened the wingtip vortex; in the latter case, a simple semi-empirical model, based on the trajectory or "streamline" of the evolving perturbation, served to explain the observations. In the absence of sweep, control on finite-span flaps did not differ significantly from their nominally twodimensional counterpart. Control from the flap produced expected lift enhancement and CL,max improvements in the absence of sweep, but these improvements degraded with the introduction of sweep.

Journal ArticleDOI
TL;DR: In this article, the results from extensive experimental investigations on turbulent flow fields and unsteady surface pressures caused by leading-edge vortices, in particular, for vortex breakdown flow, were presented.

Journal ArticleDOI
TL;DR: In this article, the roughness surface is generated by numerically generating quasi-random rough surfaces and manufacturing these surfaces using rapid prototyping technology, and measurements of the disturbances that the rough surface creates in a Blasius boundary layer are obtained for three test configurations corresponding to roughness-based Reynolds numbers of Re k = 164, 227 and 301.
Abstract: Recent experiments on transient disturbances generated by three-dimensional roughness have used spanwise-periodic arrays of geometrically simple cylindrical roughness elements. Connecting these laboratory experiments to more realistic situations requires the study of surfaces with distributed roughness. This is accomplished in this work by numerically generating quasi-random rough surfaces and manufacturing these surfaces using rapid-prototyping technology. Measurements of the disturbances that the rough surface creates in a Blasius boundary layer are obtained for three test configurations corresponding to roughness-based Reynolds numbers of Re k = 164, 227 and 301. The two lower values give laminar flow; the highest value results in localized transition approximately 140 mm downstream of the leading edge of the roughness. All three configurations exhibit transient growth of steady disturbances. Unsteady fluctuations indicate that transition in the Re k =301 configuration is likely an example of a bypass transition mechanism in which the unsteady-disturbance growth outpaces the stabilizing relaxation of the steady flow. Measurements above the roughness surface in the Re k = 227 configuration provide a phenomenological model for distributed receptivity.

Journal ArticleDOI
01 May 2008
TL;DR: In this article, two-dimensional and three-dimensional contour bumps are designed and optimized for substantial wave drag reduction for an un-swept natural laminar flow (NLF) wing (RAE5243 aerofoil section) at transonic speeds.
Abstract: Two-dimensional and three-dimensional contour bumps are designed and optimized for substantial wave drag reduction for an un-swept natural laminar flow (NLF) wing (RAE5243 aerofoil section) at transonic speeds. An NLF aerofoil wing is chosen in this study, as shock con- trol is more crucial for such wings due to the requirement of favourable pressure gradients on a substantial part of the wing. For the validation purpose and to focus on the wave drag issues, the boundary layer is assumed to be fully turbulent from the leading edge. Key bump geometrical parameters including the maximum height, the length, and the crest position have been chosen for the parameterization of the two-dimensional and three-dimensional shock control bumps. For the three-dimensional bumps, an array of the contour bumps is installed spanwise on the transonic wing and their width and spanwise spacing are chosen as additional design param- eters. Both the two-dimensional and the three-dimensional bump shapes are optimized using a discrete adjoint-based optimization method. The performance of the three-dimensional con- tour bumps are compared in detail with the similarly optimized two-dimensional bumps both at and around the design point. The results show that, for the NLF wing studied, the optimized three-dimensional bumps are as effective as the optimized two-dimensional bump in terms of total drag reduction at the given design point, despite the significant difference in their geomet- rical shapes. More importantly, in terms of the operational range for varying lift conditions for practical applications, the three-dimensional bumps outperform the two-dimensional bump by a substantial margin.

Journal ArticleDOI
TL;DR: It is shown how a spatially periodic modulation of homogeneous synaptic connections leads to an effective reduction in the speed of a traveling pulse.
Abstract: We use averaging and homogenization theory to study the propagation of traveling pulses in an inhomogeneous excitable neural network. The network is modeled in terms of a nonlocal integro- differential equation, in which the integral kernel represents the spatial distribution of synaptic weights. We show how a spatially periodic modulation of homogeneous synaptic connections leads to an effective reduction in the speed of a traveling pulse. In the case of large amplitude modulations, the traveling pulse represents the envelope of a multibump solution, in which individual bumps are nonpropagating and transient. The appearance (disappearance) of bumps at the leading (trailing) edge of the pulse generates the coherent propagation of the pulse. Wave propagation failure occurs when activity is insufficient to maintain bumps at the leading edge.

Journal ArticleDOI
TL;DR: In this paper, a new concept of passive dynamic-stall control was developed and tested on an OA209 rotorcraft airfoil during two wind-tunnel test campains in 2004 and 2005.
Abstract: A new concept of passive dynamic-stall control was developed and tested on an OA209 rotorcraft airfoil during two wind-tunnel test campains in 2004 and 2005. Small vortex generators are mounted at the leading edge of the rotor blade. At low incidence they are located close to the stagnation point and do not impact the flow field. At high angles of attack the so-called Leading Edge Vortex Generators (LEVoGs) induce longitudinal vortices which impact the suction side flow. It is shown that the use of LEVoGs can significantly increase the overall time-averaged lift while an unwanted negative pitching-moment peak is reduced compared with the clean blade case. Furthermore, overall drag is reduced at dynamic-stall conditions. Detailed analysis of the flow field by Particle Image Velocimetry and Infrared Thermography show that this is achieved by a disturbance of the dynamic-stall vortex and therefore separation is partially prevented.

Journal ArticleDOI
TL;DR: Based on the results of two-dimensional flapping wing studies, the selection of Strouhal number for steady cruising is explored in this paper, where it is suggested that the steady state propulsive efficiency of man-made systems that use flapping propulsion must be designed-in, rather than actively controlled and that sensory feedback may be more important for control during maneuvering/acceleration and play only a minor role in the regulation of a flying/swimming system's steady forward motion.

Journal ArticleDOI
Xianwu Luo1, Yao Zhang1, Junqi Peng1, Hongyuan Xu1, Weiping Yu 
TL;DR: In this paper, the effect of impeller inlet geometry on performance improvement for a boiler feed pump, which is a centrifugal pump having specific speed of 183 m·m3min−1·min− 1 and close type impeller with exit diameter of 450 mm.
Abstract: This research treats the effect of impeller inlet geometry on performance improvement for a boiler feed pump, who is a centrifugal pump having specific speed of 183 m·m3min−1·min−1 and close type impeller with exit diameter of 450 mm. The hydraulic performance and cavitation performance of the pump have been tested experimentally. In order to improve the pump, five impellers have been considered by extending the blade leading edge or applying much larger blade angle at impeller inlet compared with the original impeller. The 3-D turbulent flow inside those pumps has been analyzed basing on RNG k-ɛ turbulence model and VOF cavitation model. It is noted that the numerical results are fairly good compared with the experiments. Based on the experimental test and numerical simulation, the following conclusions can be drawn: (1) Impeller inlet geometry has important influence on performance improvement in the case of centrifugal pump. Favorite effects on performance improvement have been achieved by both extending the blade leading edge and applying much larger blade angle at impeller inlet; (2) It is suspected that the extended leading edge have favorite effect for improving hydraulic performance, and the much larger blade angle at impeller inlet have favorite effect for improving cavitation performance for the test pump; (3) Uniform flow upstream of impeller inlet is helpful for improving cavitation performance of the pump.

Journal ArticleDOI
TL;DR: In this paper, the effects of the coolant-to-mainstream blowing ratio in leading edge film cooling were analyzed and quantitatively quantified using large eddy simulation (LES) in a cylindrical leading edge with a flat after-body.

Journal ArticleDOI
TL;DR: The aim of this research paper was to evaluate two different leading edge designs by reducing the testing costs by employing state-of-the-art numerical simulations and possible guidelines for structural design including the bird impact requirements.
Abstract: One of the main structural requirements of a leading edge of a tailplane is to ensure that any significant damage caused by foreign object (i.e. birdstrike, etc...) would still allow the aircraft to land safely. In particular, leading edge must be certified for a proven level of bird impact resistance. Since the experimental tests are expensive and difficult to perform, numerical simulations can provide significant help in designing high-efficiency bird-proof structures. The aim of this research paper was to evaluate two different leading edge designs by reducing the testing costs by employing state-of-the-art numerical simulations. The material considered was a sandwich structure made up of aluminium skins and flexcore as core. Before each test was carried out, pre-test numerical analyses of birdstrike were performed adopting a lagrangian approach on a tailplane leading edge of a large scale aircraft using the MSC/Dytran solver code. The numerical and experimental correlation have shown good results both in terms of global behaviour of the test article and local evolution of some measurable parameters confirming the validity of the approach and possible guidelines for structural design including the bird impact requirements.

Patent
22 Apr 2008
TL;DR: A hollow aerofoil (30) comprises a leading edge (42), a trailing edge (44), a concave pressure surface wall (46), and a convex suction surface (48) extending from the leading edge to the trailing edge as mentioned in this paper.
Abstract: A hollow aerofoil (30) comprises an aerofoil portion (40) having a leading edge (42), a trailing edge (44), a concave pressure surface wall (46) extending from the leading edge (42) to the trailing edge (44) and a convex suction surface (48) extending from the leading edge (42) to the trailing edge (44). The concave pressure surface wall (46) and the convex suction surface wall (48) are integral and define a cavity (50). A plurality of webs (52) extend across the cavity (50) between the concave pressure surface wall (46) and the convex suction surface wall (48). At least one of the webs (52A) extends substantially perpendicularly to the concave pressure surface wall (46) and the convex suction surface wall (48) and at least one of the webs (52B) extends substantially diagonally to the concave pressure surface wall (46) and the convex suction surface wall (48).

Journal ArticleDOI
TL;DR: In this paper, the aerodynamic characteristics of NACA6409 in the vicinity of the ground were experimentally studied in a wind tunnel, where the authors measured lift and drag forces, the pitching moment, and the center of pressure with respect to various major aerodynamic parameters, such as the ground clearance, the angle of attack, the aspect ratio (AR), and the endplate type.
Abstract: The aerodynamic characteristics of NACA6409 in the vicinity of the ground were experimentally studied in a wind tunnel. Lift and drag forces, the pitching moment, and the center of pressure were measured with respect to various major aerodynamic parameters, such as the ground clearance, the angle of attack, the aspect ratio (AR), and the endplate type, which resulted in a total number of 420 conditions. In addition, a smoke trace test was conducted to visualize the flow pattern around NACA6409 in the vicinity of the ground. As a result of the ground effect and the influence of the endplate, the lift-to-drag ratio increased at low ground clearance and the center of pressure moved forward to the leading edge; that is, the endplate and ground effects were equivalent to the aerodynamic advantage that results from increasing the AR of the wing. Extended experimental results are useful for understanding the aerodynamic characteristics influenced by each aerodynamic parameter during ground effect as well as for verifying numerical simulation.

Journal ArticleDOI
TL;DR: In this paper, a numerical investigation is conducted to study leading edge film cooling with large eddy simulation (LES) where turbine blade leading edge is represented by a semi-cylindrical blunt body with compound angle of injection.

Journal ArticleDOI
TL;DR: Results indicate that Rap1, activated by PDGF, is recruited to leading edges and that Rac1 is thereby activated locally at peripheral ruffles, which is pivotal for the PDGF‐induced formation of leading edge structures and cell movement.
Abstract: Moving cells form protrusions, such as filopodia and lamellipodia, and focal complexes at leading edges, which eventually enhance cell movement. The Rho family small G proteins, Rac1, Cdc42 and RhoA, are involved in the formation of these leading edge structures. We investigated the role of another small G protein Rap1 in the platelet-derived growth factor (PDGF)-induced formation of leading edge structures and cell movement. Upon stimulation of NIH3T3 cells by PDGF, leading edge structures were formed and Necl-5, integrin αVβ3, and PDGF receptor were accumulated at leading edges. Rap1, upstream regulators of Rap1 such as Crk and C3G, and a downstream effector RalGDS, were accumulated at peripheral ruffles over lamellipodia. Over-expression of Rap1GAP, which inactivates Rap1, and knockdown of Rap1 inhibited the PDGF-induced formation of leading edge structures, accumulation of these molecules, and cell movement. In addition, Rap1 activation subsequently induced accumulation of Rac1, Vav2 and PAK at peripheral ruffles, which was inhibited by Rap1GAP and knockdown of Rap1. These results indicate that Rap1, activated by PDGF, is recruited to leading edges and that Rac1 is thereby activated locally at peripheral ruffles. This process is pivotal for the PDGF-induced formation of leading edge structures and cell movement.

Journal ArticleDOI
TL;DR: In this article, an effective and verified flow control process using direct current surface discharge is summarized, based on a small electromagnetic perturbation to the growth rate of the displacement thickness of a shear layer that is strongly amplified by a subsequent pressure interaction.
Abstract: Plasma-fluid-dynamic interaction has been shown to be a viable mechanism for hypersonic flow control. An effective and verified flow control process using direct current surface discharge is summarized. The operating principle is based on a small electromagnetic perturbation to the growth rate of the displacement thickness of a shear layer that is strongly amplified by a subsequent pressure interaction. The aerodynamic control is delivered in less than a millisecond time frame and produces no parasitic effect when deactivated. The magnitude of the resultant aerodynamic force and moment can be significant and does not require a large amount of power for plasma generation to overcome the inefficient ionizing process, thus reducing the weight of a high-speed vehicle. The electromagnetic perturbation is derived from a surface gas discharge with or without an externally applied magnetic field. An embedded plasma actuator near the leading edge of a flat plate has produced high surface pressure equivalent to more than a 5 deg flow deflection at Mach 5, and the flow control effectiveness will increase with an increasing oncoming Mach number. The detailed flow structure of weakly ionized airstreams has been investigated by a combination of experimental effort and computational simulation solving the magneto-fluid-dynamic equations in the low magnetic Reynolds number limit with a drift-diffusion plasma model. The identical plasma actuator is investigated as a variable geometry cowl of a hypersonic inlet. All phenomena are replicated by computational results and are fully validated by experimental observations.

Journal ArticleDOI
TL;DR: In this article, an ionization-induced phase-matching condition is used to limit the harmonic output on the leading edge of an 800 nm driver laser pulse under moderately intense focusing conditions (7×1014 W/cm2).
Abstract: High-order harmonic emission can be confined to the leading edge of an 800 nm driver laser pulse under moderately intense focusing conditions (7×1014 W/cm2) (Pfeifer et al. in Opt. Express 15:17120, 2007). Here, the experimentally observed curtailment of harmonic production on the leading edge of the driver pulse is shown to be controlled by an ionization-induced phase-matching condition. The transient plasma density inherent to the process of high-harmonic generation terminates the harmonic emission by an ultrafast loss of phase matching on the leading edge of the laser pulse. The analysis is supported by a reconstruction of the in situ intensity envelope of the driver pulse with attosecond temporal resolution, performed by measurements of the carrier-envelope phase dependence of individual half-cycle harmonic cutoffs. The method opens the way to wavelength-tunable isolated attosecond pulse generation.

Patent
27 Oct 2008
TL;DR: ActiveActive Circulation Control (ACC) of aerodynamic structures such as a turbine blade, uses unsteady or oscillatory flow from either synthetic jets or pulsed jets to modify a velocity profile of the blade as mentioned in this paper.
Abstract: Active Circulation Control (ACC) of aerodynamic structures, such as a turbine blade, uses unsteady or oscillatory flow from either synthetic jets or pulsed jets to modify a velocity profile of the blade. The blade includes an opening disposed in a surface of the blade at a location proximate to a trailing edge, a leading edge, or both the trailing edge and the leading edge of the blade. An active flow control device in fluid communication with the opening produces a wall-jet of pulsed fluid that flows over the trailing edge, the leading edge, or both the trailing and leading edges of the blade and modify the velocity profile of the blade.

Journal ArticleDOI
TL;DR: In this paper, a hybrid reasoning methodology is applied to a complex aerospace structure, and its effectiveness is assessed in identifying and locating the position of impacts using passive piezoceramic sensors.
Abstract: A hybrid reasoning methodology is applied to a complex aerospace structure, and its effectiveness is assessed in identifying and locating the position of impacts. Part of a commercial aircraft wing flap is impacted and time-varying strain response data from the structure are sensed using passive piezoceramic sensors. This structure can be regarded as a small scale version of part of a wing span with the corresponding features being a leading edge and trailing edge. The trailing edge is composed of aluminium skins with an aluminium honeycomb core, the leading edge of composite skins with a light weight honeycomb core, and the central section of thin composite material. Nine sensors, to detect time-varying strain response data, are distributed over the surface of the flap; two on the leading edge, two on the trailing edge, and five in the central section. The methodology combines the use of: (i) Case-Based Reasoning; in a `learning mode', an initial casebase is created with the principal features of the imp...