Showing papers on "Leading edge published in 1999"

Optimal disturbances and bypass transition in boundary layers

Abstract: Streamwise streaks are ubiquitous in transitional boundary layers, particularly when subjected to high levels of free-stream turbulence. Using the steady boundary-layer approximation, the upstream disturbances experiencing maximum spatial energy growth are numerically calculated. The calculations use techniques commonly employed when solving optimal-control problems for distributed parameter systems. The calculated optimal disturbances consist of streamwise vortices developing into streamwise streaks. The maximum spatial energy growth was found to scale linearly with the distance from the leading edge. Based on these results, a simple model for prediction of transition location is proposed. Available experiments have been used to correlate the single constant appearing in the model.

Dimensional and mechanical dynamics of active and stable edges in motile fibroblasts investigated by using atomic force microscopy

Abstract: The atomic force microscope (AFM) was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture. Such dynamics closely paralleled the results of earlier studies employing video microscopy that indicated that the AFM force-mapping technique does not appreciably perturb these dynamics. Force scans permitted height determinations of active and stable edges. Whereas the profiles of active edges are flat with average heights of 0.4–0.8 μm, stable edges smoothly ascend to 2–3 μm within about 6 μm of the edge. In the region of the leading edge, the height fluctuates up to 50% (SD) of the mean value, much more than the stable edge; this fluctuation presumably reflects differences in underlying cytoskeletal activity. In addition, force mapping yields an estimate of the local Young’s modulus or modulus of elasticity (E, the cortical stiffness). This stiffness will be related to “cortical tension,” can be accurately calculated for the stable edges, and is ≈12 kPa in this case. The thinness of the leading edge precludes accurate estimation of the E values, but within 4 μm of the margin it is considerably smaller than that for stable edges, which have an upper limit of 3–5 kPa. Although blebbing cannot absolutely be ruled out as a mechanism of extension, the data are consistent with an actin polymerization and/or myosin motor mechanism in which the average material properties of the extending margin would be nearly constant to the edge. Because the leading edge is softer than the stable edge, these data also are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.

Flight Data for Boundary-Layer Transition at Hypersonic and Supersonic Speeds

Abstract: Published e ight data for boundary-layer transition at hypersonic speeds are surveyed. The survey is limited to measurements reported in the open literature and carried out at hypersonic and high-supersonic speeds, on vehicles for which ablation is believed to be negligible or small. The emphasis is on work that may be suitable for validation of advanced transition-estimation methods that are based on simulation of the physical mechanisms, such as e N , the parabolized stability equations, and direct numerical simulations. Brief discussions are presented for each report. Known comparisons to the advanced simulation methods are also presented. Nomenclature Me = Mach number at the boundary-layer edge Res = Reynolds number at transition onset, based on arc length from the leading edge and local conditions at the boundary-layer edge ReT = Reynolds number at transition onset, based on arc length and conditions at the boundary-layer edge ReT/ft = unit Reynolds number per foot, at the boundary-layer edge at transition onset Reµ = Reynolds number at transition, usually onset, based on momentum thickness and conditions at the boundary-layer edge Te = temperature at the boundary-layer edge Tr = recovery temperature at the wall Tw = wall temperature xT = arc length to transition onset, from the nose µc = cone half-angle, deg

Relationship between Arp2/3 Complex and the Barbed Ends of Actin Filaments at the Leading Edge of Carcinoma Cells after Epidermal Growth Factor Stimulation

Abstract: Using both light and high resolution electron microscopy, we analyzed the spatial and temporal relationships between the Arp2/3 complex and the nucleation activity that is required for lamellipod extension in mammary carcinoma cells after epidermal growth factor stimulation. A rapid two- to fourfold increase in filament barbed end number occurs transiently after stimulation and remains confined almost exclusively to the extreme outer edge of the extending lamellipod (within 100–200 nm of the plasma membrane). This is accompanied by an increase in filament density at the leading edge and a general decrease in filament length, with a specific loss of long filaments. Concomitantly, the Arp2/3 complex is recruited with a 1.5-fold increase throughout the entire cortical filament network extending 1–1.5 μm in depth from the membrane at the leading edge. The recruitment of the Arp2/3 complex at the membrane of the extending lamellipod indicates that Arp2/3 may be involved in initial generation of growing filaments. However, only a small subset of the complex present in the cortical network colocalizes near free barbed ends. This suggests that the 100–200-nm submembraneous compartment at the leading edge of the extending lamellipod constitutes a special biochemical microenvironment that favors the generation and maintenance of free barbed ends, possibly through the locally active Arp2/3 complex, severing or decreasing the on-rate of capping protein. Our results are inconsistent with the hypothesis suggesting uncapping is the dominant mechanism responsible for the generation of nucleation activity. However, they support the hypothesis of an Arp2/3-mediated capture of actin oligomers that formed close to the membrane by other mechanisms such as severing. They also support pointed-end capping by the Arp2/3 complex, accounting for its wide distribution at the leading edge.

The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics

Abstract: The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubblelike recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow, resulting from the contraction of the bubblelike structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise, and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

Role of Blade Passage Flow Structurs in Axial Compressor Rotating Stall Inception

Abstract: The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors' knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (the movement of the tip clearance vortex forward of the leading edge) depends upon local flow phenomena related to the tip clearance with the implication that for this and possibly other stall mechanisms the flow structure within the blade passages must be addressed to explain the stability of an axial compression system that exhibits such short length-scale disturbances.

Investigation of unsteady sheet cavitation and cloud cavitation mechanisms

Abstract: Sheet cavitation on a foil section and, in particular, its unsteady characteristics leading to cloud cavitation, were experimentally investigated using high-speed visualizations and fluctuating pressure measurements. Two sources of sheet cavitation instability were evidenced, the re-entrant jet and small interfacial waves. The dynamics of the re-entrant jet was studied using surface electrical probes. Its mean velocity at different distances from the leading edge was determined and its role in promoting the unsteadiness of the sheet cavitation and generating large cloud shedding was demonstrated. The effect of gravity on the dynamics of the re-entrant jet and the development of interfacial perturbations were examined and interpreted. Finally, control of cloud cavitation using various means, such as positioning a tiny obstacle (barrier) on the foil surface or performing air injection through a slit situated in the vicinity of the leading edge, was investigated

Serial elastic elements in the damselfly wing: mobile vein joints contain resilin

Abstract: Two main types of joints occur in the damselfly wing: mobile and immobile. Some longitudinal veins (RP2–, RP3&4–, and MP–) are elastically joined with cross veins, whereas other longitudinal veins (IR1+, IR2+, MA+, CuA'+) are firmly joined with cross veins. In this study we mapped the distribution of serial elastic elements in the wing. The occurrence of resilin, a rubberlike protein, in mobile joints suggests that the automatic twisting mechanism of the leading edge by aerodynamic force works not by flexibility but by the elasticity of these joints. First, it should result in elastic energy storage in the distal areas of the wing. Second, serial elastic elements of wing presumably act as dampers of an aerodynamic force, which are responsible for gradual twisting of the leading edge.

Regional regulation of microtubule dynamics in polarized, motile cells

Abstract: Microtubules are known to be required for locomotion of mammalian cells, and recent experiments demonstrate that suppression of microtubule dynamic turnover reduces the rate of cell motility and induces wandering of growth cones [Liao et al., 1995: J Cell Sci. 108:3473-3483; Tanaka et al., 1995: J Cell Biol. 128:139-155]. To determine how microtubule dynamic instability behavior contributes to directed cell locomotion, the behavior of individual microtubules has been directly observed and quantified at leading and lateral edges of hepatocyte growth factor-treated motile cells. Microtubules extended into newly formed protrusions at the leading edge; these "pioneer" microtubules [Waterman-Storer and Salmon, 1997: J Cell Biol. 139:417-434] showed persistent growth when compared with microtubules in non-leading, lateral edges. The percentage of total observation time spent in the growth phase was 68.2% at the leading edge compared with 32.0% in non-leading edges, and net microtubule elongation was observed in lamellipodia at the leading edge. The frequency of catastrophe transitions was threefold greater and the average number of transitions/microtubule/min was twofold greater in non-leading edges, as compared with the leading edge. These observations demonstrate that pioneer microtubules that enter newly formed lamellipodia at the leading edge of motile cells are characterized by persistent growth excursions, and directly demonstrate that the frequency of catastrophe transitions can be regionally regulated in polarized motile cells. The data indicate that region specific differences in the organization and dynamics of actin filaments may regulate microtubule dynamic instability behavior in vivo.

A coolable airfoil for a gas turbine engine

Abstract: A hollow airfoil 12 is provided having a leading edge 18, a trailing edge 20, and a wall 22 including a suction side portion 24 and a pressure side portion 26. The wall 22, which includes an interior surface 40 and an exterior surface 42, surrounds a first cavity 30 and a second cavity 32, separated from one another by a rib 34 extending between the suction side and pressure side wall portions. The first cavity 30 is contiguous with the leading edge 18. The airfoil 12 further includes a coolant flow splitter 44 attached to the wall interior surface 40 within the first cavity 30, and at least one metering orifice 50 disposed in the rib 34. The metering orifice(s) 50 are substantially aligned with the coolant flow splitter 44, such that cooling air passing through the metering orifice(s) 50 encounters the flow splitter 44. The flow splitter 44 splits the cooling air flow and directs it along the wall interior surface 40.

Receptivity to surface roughness near a swept leading edge

Abstract: The formation of stationary cross flow vortices in a three-dimensional boundary layer due to surface roughness located near the leading edge of a swept wing is investigated using numerical solutions of the compressible Navier–Stokes equations. The numerical solutions are used to evaluate the accuracy of theoretical receptivity predictions which are based on the parallel-flow approximation. By reformulating the receptivity theory to include the effect of surface curvature, it is shown that convex surface curvature enhances receptivity. Comparisons of the parallel-flow predictions with Navier–Stokes solutions demonstrate that non-parallel effects strongly reduce the initial amplitude of stationary cross flow vortices. The curvature and non-parallel effects tend to counteract one another; but, for the cases considered here, the non-parallel effect dominates leading to significant over-prediction of receptivity by parallel-flow receptivity theory. We conclude from these results that receptivity theories must account for non-parallel effects in order to accurately predict the amplitude of stationary crossflow instability waves near the leading edge of a swept wing.

Leaned and swept fan outlet guide vanes

Abstract: A gas turbine engine fan assembly has a plurality of axially swept fan exit guide vanes circumferentially disposed around an axially extending centerline, a plurality of fan frame struts having axially swept strut leading edges and circumferentially disposed around the centerline directly aft of the exit guide vanes, and an axially extending annular gap between the trailing edges of the fan exit guide vanes and the strut leading edges. Each of the fan exit guide vanes has pressure and suction sides, vane trailing edges, and is circumferentially leaned such that the pressure side facing radially inward. Preferably, the axially swept vane trailing edges and the axially swept strut leading edges generally conform to each other in shape. An annular splitter is radially disposed at a spanwise position to split airflow from the fan into fan bypass airflow and core engine airflow and includes a splitter leading edge preferably positioned aft of the strut leading edges.

Wind turbine blade with vortex generator

Abstract: A wind turbine blade is provided with a plurality of vortex generators (3) projecting from its lee surface (2) for controlling the boundary layer separation. Each vortex generator (3) is formed as a solid and in a top view substantially wedge-shaped body defined by two lateral faces (4, 5) arranged substantially perpendicular to the surface of the blade, when seen in a top view said faces extending mutually divergently from a tip (6), which faces toward the leading edge (1) of the blade, to the trailing edge (7) of the blade. Each vortex generator (3) is furthermore in downstream direction defined by a rear face (8) and in upstream direction by a top face (9). When seen in the direction from the tip (6) toward the rear face (8) along a transverse plane of the blade, the top face (9) extends non-convergently such that the height (h2) at the tip (6) is less or equal to its height (h1) at the rear face (8).

Effect of rail/armature geometry on current density distribution and inductance gradient

Abstract: The distribution of current in the conductors which is affected by the geometry of the armature and the velocity of the armature plays an important role in the performance of an electromagnetic launcher. In the early launching stage the current tends to flow on the outer surfaces of the conductors, resulting in high local current densities. Later in the launch, the tendency for current to concentrate on the surface is driven by the velocity skin effect. High current densities produce high local heating and, consequently, increased armature wear. This paper investigates the effects of rail/armature geometry on current density distribution and launcher inductance gradient (L'). Three geometrical parameters are used to characterize the railgun systems. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density and L' for various configurations are compared.

Heating device with resistive elements for an aerodynamic profile

Abstract: This concerns a heating device for an aerodynamic profile ( 10 ) including, incorporated into the aerodynamic profile near the leading edge ( 6 ) of the aerodynamic profile, several resistive elements forming a first set ( 18 ) of resistive elements ( 14,15 ) running approximately parallel to the leading edge, arranged in a way to form a de-icing circuit. The device includes in addition a second set ( 19 ) of resistive elements ( 16,17 ) incorporated into the aerodynamic profile and arranged as an anti-icing circuit. The two circuits ( 18,19 ) are independent and the relative positions of their elements are a function of the design of the profile.

Hollow airfoil for a gas turbine engine

Abstract: A hollow airfoil is provided which includes a body having an external wall and an internal cavity. The external wall includes a suction side portion and a pressure side portion. The portions extend chordwise between a leading edge and a trailing edge and spanwise between an inner radial surface and an outer radial surface. A stagnation line extends along the leading edge. A plurality of cooling apertures, disposed spanwise along the leading edge. According to one aspect of the present invention, the apertures extend through the external wall along a helical path. According to another aspect of the present invention, the apertures are alternately directed towards the suction side portion and the pressure side portions of the airfoil.

Apparatus and method for inhibiting radial transfer of core gas flow within a core gas flow path of a gas turbine engine

Abstract: A method for inhibiting radial transfer of core gas flow away from a center radial region and toward the inner and outer radial boundaries of a core gas flow path within a gas turbine engine is provided that includes the steps of: (1) providing a flow directing structure that includes an airfoil that abuts a wall surface, said airfoil having a leading edge, a pressure side, and a suction side; and (2) increasing the velocity of the core gas flow in the area where the leading edge of the airfoil abuts the wall. Increasing the velocity of the core gas flow in the area where the leading edge of the airfoil abuts the wall impedes the formation of a pressure gradient along the surface of the airfoil that forces core gas from the center region of the core gas toward the wall. The apparatus includes apparatus for diverting core gas flow away from the area where the airfoil abuts the wall.

Direct numerical simulation of a puff and a slug in transitional cylindrical pipe flow

Abstract: A direct numerical simulation of transitional pipe flow is carried out with the help of a spectral element method and used to investigate the localized regions of ‘turbulent’ flow that are observed in experiments. Two types of such regions can be distinguished: the puff and the slug. The puff, which is generally found at low values of the Reynolds numbers, is simulated for Re = 2200 where the Reynolds number Re is based on the mean velocity UB and pipe diameter D. The slug occurs at a higher Reynolds number and it is simulated for Re = 5000. The computations start with a laminar pipe flow to which is added a prescribed velocity disturbance at a given axial position and for a finite time. The disturbance then evolves further into a puff or slug structure.The simulations confirm the experimentally observed fact that for a puff the velocity near the leading edge changes more gradually than for a slug where an almost discontinuous change is observed. The positions of the leading and trailing edges of the puff and slug are computed from the simulations as a function of time. The propagation velocity of the leading edge is found to be constant and equal to 1.56UB and 1.69UB for the puff and slug, respectively. For the trailing edge the velocity is found to be 0.73UB and 0.52UB, respectively. By rescaling the simulation results obtained at various times to a fixed length, we define an ensemble average. This method is used to compute the average characteristics of the puff and slug such as the spatial distribution of the mean velocity, the turbulent velocity fluctuations and also the wall shear stress. By computing particle trajectories we have investigated the entrainment and detrainment of fluid by a puff and slug. We find that the puff detrains through its trailing edge and entrains through its leading edge. The slug entrains fluid through its leading and through most of its trailing edge. As a consequence the fluid inside the puff is constantly exchanged with fluid outside whereas the fluid inside a slug remains there. These entrainment/detrainment properties which are in agreement with the measurements of Wygnanski & Champagne (1973) imply that the puff has the characteristics of a wave phenomenon while the slug can be characterized more as a material property which travels with the flow.Finally, we have investigated in more detail the velocity field within the puff. In a coordinate system that travels with the mean velocity we find recirculation regions both near the trailing and leading edges which agrees at least qualitatively with experimental data. We also find streamwise vortices, predominantly in the trailing-edge region which have been also observed in experiments and which are believed to play an important role in the dynamics of the transition process.

Golf club wood head with optimum aerodynamic structure

Abstract: A golf club wherein in one embodiment the club head (50) is preferably molded from a clear acrylic material or polymeric material or a high tech metal alloy wherein a plurality of elongated elliptical or v-shaped gently flaring grooves or indentations (11, 12) extend normal to the striking surface (17) and are embedded in at least the crown (19) and sole (26) of the club head (50). These grooves (11, 12) may be present in the toe surface (16) in larger club heads, such as drivers. These grooves (11, 12) initiate from just behind the striking surface (17) or leading edge and extend rearwardly toward the back (20) of the club wood head (50). The grooves (11, 12) create a corresponding plurality of vortices during the golf swing which redirect and accelerate air flow rearwardly away from the back (20) of the club head (50), reducing wind resistance and eliminating induced drag of the moving club head (50), thereby increasing thrust which in turn increases the overall distance that a golf ball is capable of traveling during a given shot. In one embodiment of the invention, a metal housing (352) or shell is provided with an acrylic insert to achieve increased performance and durability.

Frequency tuned hybrid blade

Abstract: A fan blade includes a metal airfoil having first and second opposite sides extending radially between a root and tip, and axially between a leading edge and a trailing edge. The airfoil further includes a plurality of pockets disposed in the first side and separated by corresponding ribs. A filler is bonded in the pocket, and is coextensive with the airfoil first side. Radial and diagonal ribs respectively intersect solely each other for selectively increasing torsional and bending stiffness to increase frequency margin between adjacent torsional and bending resonant modes of vibration.

Active Control of Flow Separation Over an Airfoil

Abstract: Designing an aircraft without conventional control surfaces is of interest to aerospace community. In this direction, smart actuator devices such as synthetic jets have been proposed to provide aircraft maneuverability instead of control surfaces. In this article, a numerical study is performed to investigate the effects of unsteady suction and blowing on airfoils. The unsteady suction and blowing is introduced at the leading edge of the airfoil in the form of tangential jet. Numerical solutions are obtained using Reynolds-Averaged viscous compressible Navier-Stokes equations. Unsteady suction and blowing is investigated as a means of separation control to obtain lift on airfoils. The effect of blowing coefficients on lift and drag is investigated. The numerical simulations are compared with experiments from the Tel-Aviv University (TAU). These results indicate that unsteady suction and blowing can be used as a means of separation control to generate lift on airfoils.

Centrifugal pump with solids cutting action

Abstract: A centrifugal pump has an impeller rotatable by means of a drive shaft. The impeller has a plurality of radially extending vanes connected to a hub and a partial back shroud with sharpened leading edges. The pump has a pump casing with a back plate adjacent to the back side of the impeller. Spiral grooves on the back plate interact with the sharpened edges on the back shroud to aid in protecting the area between the back plate and the impeller by cutting of solids and expulsion of solids through an output port. Cutting bars on the front plate of the casing project into the pump intake and interact with front edges of the vanes to cut incoming solids in a liquid mixture. A preferred form of impeller has vanes with sharpened leading edges that extend in a generally radial plane. These vanes sweep backwardly from their leading edges and each vane is given a double twist between the leading edge and its trailing edge. This form of impeller has both an effective slicing action and an efficient transmission of kinetic energy to the fluid.

Aerial transport method and apparatus

Abstract: Apparatus for transporting a load (24) between source and destination locations, comprising an aircraft having a body (11), power plant (12) carried by the body (11) to drive the aircraft both generally vertically and also generally horizontally, the aircraft also having a wing structure (14-15) that has a leading edge remaining presented in the direction of flight; and load pick-up, carry and set-down means (22) connected to the aircraft to elevate the load (24) from the source location, transport the elevated and air-borne load (24) generally horizontally, and set the load (24) down at the destination location, the body (11) and power plant (12) configured for vertical flight mode to elevate and set down the load (24), and for generally horizontal flight mode to transport the elevated load (24) generally horizontally below the level of the aircraft body (11).

Effects of leading-edge ice accretion geometry on airfoil performance

Abstract: A systematic study of the effect of simulated ice shape geometry on airfoil aerodynamics was performed. A wind tunnel test was performed using a flapped NLF( l)-0414 airfoil where aerodynamic parameters including hinge moment were measured. The ice shapes tested were designed to simulate a single glaze ice horn with leading-edge radius, size and airfoil surface location varied. In all nine ice simulations were tested at six different leading edge locations. The objective of this research was to determine the sensitivity of iced airfoil aerodynamics to ice shape geometry. Configurations were also tested at three different Reynolds numbers (0.5, 1.0, and 1.8~10~). It was determined that ice horn leading-edge radius had only a small effect on airfoil aerodynamics. However, the aerodynamic performance was very sensitive to ice shape size and location. An almost linear relationship between loss in maximum lift and ice horn location was found with the largest loss at the furthest location back on the upper surface. Reynolds number was found to have little effect on the aerodynamic results on the airfoil with simulated ice shapes.

Coriolis turbulator blade

Abstract: A method of placing turbulators in a turbine rotor blade includes placing slant turbulators in a radial flow channel offset circumferentially from the blade leading edge. The slant turbulators are all inclined radially inward toward the blade trailing edge for directing coolant along the turbulators co-directionally with Coriolis flow inside the offset channel. In a specific embodiment, turbulator chevrons are also placed in a radial flow channel axially aligned with the blade leading edge consistent with the Coriolis flow therein.

Horizontal Axis Wind Turbine Aerodynamics: Three-Dimensional, Unsteady, and Separated Flow Influences

Abstract: Surface pressure data from the National Renewable Energy Laboratory's ''Unsteady Aerodynamics Experiment'' were analyzed to characterize the impact of three-dimensionality, unsteadiness, and flow separation effects observed to occur on downwind horizontal axis wind turbines (HAWT). Surface pressure and strain gage data were collected from two rectangular planform blades with S809 airfoil cross-sections, one flat and one twisted. Both blades were characterized by the maximum leading edge suction pressure and by the azimuth, velocity, and yaw at which it occurred. The occurrence of dynamic stall at all but the inboard station (30% span) shows good quantitative agreement with the theoretical limits on inflow velocity and yaw that should yield dynamic stall events. A full three-dimensional characterization of the surface pressure topographies combined with flow visualization data from surface mounted tufts offer key insights into the three-dimensional processes involved in the unsteady separation process and may help to explain the discrepancies observed with force measurements at 30% span. The results suggest that quasi-static separation and dynamic stall analysis methods relying on purely two-dimensional flow characterizations may not be capable of simulating the complex three-dimensional flows observed with these data.

Impact of Film-Cooling Jets on Turbine Aerodynamic Losses

Abstract: This paper documents a computational investigation of the aerodynamic impact of film cooling on a linear turbine airfoil cascade. The simulations were for single row injection on both the pressure and suction surfaces, downstream of the leading edge region. The cases match experimental efforts previously documented in the open literature. Results were obtained for density ratio equal to 1.0 and 2.0, and a blowing ratio range from 0.91 to 6.6. The domain included the passage flow as well as the film-hole and blade interior. The simulation used a dense, high-quality, unstructured hybrid–topology grid, comprised of hexahedra, tetrahedra, prisms and pyramids. The processing was performed with a pressure-correction solution procedure and a second–order discretization scheme. Turbulence closure was obtained using standard, RNG, and “realizable” k-e models, as well as a Reynolds stress model. Results were compared to experimental data in terms of total pressure loss downstream of the blade row. Flow mechanisms responsible for the variation of aerodynamic losses due to suction and pressure surface coolant injection are documented. The results demonstrate that computational methods can be used to accurately predict losses on film–cooled airfoils.Copyright © 1999 by ASME