Showing papers on "Airfoil published in 1997"

Design and experimental results for the S809 airfoil

Abstract: A 21-percent-thick, laminar-flow airfoil, the S809, for horizontal-axis wind-turbine applications, has been designed and analyzed theoretically and verified experimentally in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. The two primary objectives of restrained maximum lift, insensitive to roughness, and low profile drag have been achieved. The airfoil also exhibits a docile stall. Comparisons of the theoretical and experimental results show good agreement. Comparisons with other airfoils illustrate the restrained maximum lift coefficient as well as the lower profile-drag coefficients, thus confirming the achievement of the primary objectives.

High-Lift Low Reynolds Number Airfoil Design

Abstract: A new high-lift airfoil design philosophy has been developed and experimentally validated through wind-tunnel tests A key element of the high-lift design philosophy was to make use of a concave pressure recovery with aft loading Three codes for airfoil design and analysis (PROFOIL, the Eppler code, and ISES) were used to design the example S1223 high-lift airfoil for a Reynolds number of 2 3 10 5 In windtunnel tests, the new airfoil yielded a maximum lift coefe cient of 22 With vortex generators and a 1% chord Gurney eap (used separately), the Cl,max increased to 23 The airfoil demonstrates the rather dramatic gains in Cl,max over those airfoils previously used for high-lift low Reynolds number applications

Boundary Layer Development in Axial Compressors and Turbines: Part 1 of 4—Composite Picture

Abstract: Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components. Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of our experimental findings by using sketches to show how boundary layers develop on compressor and turbine blading. Parts 2 and 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and discusses comparisons with experimental data. Readers not interested in experimental detail can go directly from Part 1 to Part 4. For both compressor and turbine blading, the experimental results show large extents of laminar and transitional flow on the suction surface of embedded stages, with the boundary layer generally developing along two distinct but coupled paths. One path lies approximately under the wake trajectory while the other lies between wakes. Along both paths the boundary layer clearly goes from laminar to transitional to turbulent. The wake path and the non-wake path are coupled by a calmed region, which, being generated by turbulent spots produced in the wake path, is effective in suppressing flow separation and delaying transition in the non-wake path. The location and strength of the various regions within the paths, such as wake-induced transitional and turbulent strips, vary with Reynolds number, loading level, and turbulence intensity. On the pressure surface, transition takes place near the leading edge for the blading tested. For both surfaces, bypass transition and separated-flow transition were observed. Classical Tollmien-Schlichting transition did not play a significant role. Comparisons of embedded and first-stage results were also made to assess the relevance of applying single-stage and cascade studies to the multistage environment. Although doing well under certain conditions, the codes in general could not adequately predict the onset and extent of transition in regions affected by calming. However, assessments are made to guide designers in using current predictive schemes to compute boundary layer features and obtain reasonable loss predictions.

Airfoil Section Characteristics at a Low Reynolds Number

Abstract: The aerodynamic characteristics of airfoils operating at Re = 4 X 10 3 were examined, varying the parameters related to the airfoil shape such as thickness, camber, and roughness. Airfoils with good aerodynamic performance at this Re have the following shape characteristics : (1) they are thinner than airfoils for higher Re numbers, (2) they have a sharp leading edge, and (3) they have a camber of about five percent with its maximum camber at about mid-chord. The characteristics of airfoils are strongly affected by leading edge vortices. The measured two-dimensional airfoil characteristics indicate that the planform, which greatly affects the flight performance of the three-dimensional wing at high Reynolds numbers, has little effect on the flight performance at this Reynolds number.

Boundary Layer Development in Axial Compressors and Turbines: Part 3 of 4— LP Turbines

Abstract: This is Part Three of a four-part paper. It begins with Section 11.0 and continues to describe the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this part, we present the experimental evidence that we used to construct the composite picture for LP turbines that was given in the discussion in Section 5.0 of Part 1. We present and interpret the data from the surface hot-film gages and the boundary layer surveys for the baseline operating condition. We then show how this picture changes with variations in Reynolds number, airfoil loading, and nozzle-nozzle clocking.

Turbine blade with enhanced cooling and profile optimization

Abstract: A first-stage turbine blade includes an airfoil having a profile according to Table I. The airfoil has a plurality of cooling air passages extending linearly from the root portion to the tip portion of the airfoil. The blade includes a shank having a pair of cavities in communication through the blade dovetail with a plenum in the wheel space for supplying cooling air to the passages in the airfoil. The cooling passages in the airfoil terminate in a recess at the tip portion which has an opening adjacent the trailing edge of the airfoil and along the suction side to enable egress of cooling air into the hot gas stream on the low pressure side of the airfoil. The majority of the cooling passages are turbulated. Certain of those passages are arranged in rows lying adjacent to the pressure and suction sides of the airfoil.

Eigenmode Analysis in Unsteady Aerodynamics: Reduced Order Models

Abstract: In this article, we review the status of reduced order modeling of unsteady aerodynamic systems Reduced order modeling is a conceptually novel and computationally efficient technique for computing unsteady flow about isolated airfoils, wings, and turbomachinery cascades Starting with either a time domain or frequency domain computational fluid dynamics (CFD) analysis of unsteady aerodynamic or aeroacoustic flows, a large, sparse eigenvalue problem is solved using the Lanczos algorithm Then, using just a few of the resulting eigenmodes, a Reduced Order Model of the unsteady flow is constructed With this model, one can rapidly and accurately predict the unsteady aerodynamic response of the system over a wide range of reduced frequencies Moreover, the eigenmode information provides important insights into the physics of unsteady flows Finally, the method is particularly well suited for use in the active control of aeroelastic and aeroacoustic phenomena as well as in standard aeroelastic analysis for flutter or gust response Numerical results presented include: 1) comparison of the reduced order model to classical unsteady incompressible aerodynamic theory, 2) reduced order calculations of compressible unsteady aerodynamics based on the full potential equation, 3) reduced order calculations of unsteady flow about an isolated airfoil based on the Euler equations, and 4) reduced order calculations of unsteady viscous flows associated with cascade stall flutter, 5) flutter analysis using the Reduced Order Model This review article includes 25 references

Practical Three-Dimensional Aerodynamic Design and Optimization Using Unstructured Meshes

Abstract: A methodology for performing optimization on three-dimensional unstructured grids based on the Euler equations is presented. The same, low-memory-cost explicit relaxation algorithm is used to resolve the discrete equations that govern the flow, linearized direct, and adjoint problems. The analysis scheme is a high-resolution local-extremum-diminishing-type scheme that uses Roe decomposition for the dissipative fluxes. Mesh movement is performed in such a way that optimization of arbitrary geometries is allowed. The parallelization of the algorithm, which permits its extension to optimization of realistic, complete aircraft geometries, is presented. Two sample optimizations are performed. The flrst is the inverse design of a transonic wing/body configuration using a surface target pressure distribution found by analyzing the geometry for known design variable deflections. The second exercise is the inverse design of a business jet configuration consisting of wing, body, strut, nacelle, horizontal fin, and vertical fin. The surface target pressure distribution in this case is provided by an analysis of the configuration with no strut-nacelle.

Poly-component blade for a gas turbine

Abstract: A lightweight, impact-resistant gas turbine blade, such as an aircraft engine fan blade, has an airfoil portion (14). The airfoil portion includes a metallic section (28) consisting essentially of metal and at least one panel section (38) not consisting essentially of metal. The metallic section extends from generally the blade root to generally the blade tip. Each panel section is an elastomeric section. Preferably, the metallic section and the at-least-one panel section only together define a generally airfoil shape.

CFD calculations of S809 aerodynamic characteristics

Abstract: Steady-state, two-dimensional CFD calculations were made for the S809 laminar-flow, wind-turbine airfoil using the commercial code CFD-ACE. Comparisons of the computed pressure and aerodynamic coefficients were made with wind tunnel data from the Delft University 1.8 m x 1.25 m low-turbulence wind tunnel. This work highlights two areas in CFD that require further investigation and development in order to enable accurate numerical simulations of flow about current generation wind-turbine airfoils: transition prediction and turbulence modeling. The results show that the laminar-to-turbulent transition point must be modeled correctly to get accurate simulations for attached flow. Calculations also show that the standard turbulence model used in most commercial CFD codes, the k-{epsilon} model, is not appropriate at angles of attack with flow separation.

Inverse and Direct Airfoil Design Using a Multiobjective Genetic Algorithm

Abstract: Some of the advantages and drawbacks of genetic algorithms applications to aerodynamic design are demonstrated. A numerical procedure for the aerodynamic design of transonic airfoils by means of genetic algorithms, with single-point, multipoint, and multiobjective optimization capabilities, is presented. In the ® rst part, an investigation on the relative ef® ciency of different genetic operators combinations is carried out on an aerodynamic inverse design problem. It is shown how an appropriate tuning of the algorithm can provide improved performances, better adaption to design space size and topology, and variables cross correlation. In the second part, the multiobjective approach to design is introduced. The problem of the optimization of the drag rise characteristics of a transonic airfoil is addressed and dealt with using a single point, a multipoint, and a multiobjective approach. A comparison between the results obtained using the three different strategies is ® nally established, showing the advantages of multiobjective optimization.

Inverse and Direct Airfoil Design Using a Multiobjective Genetic Algorithm

Abstract: Some of the advantages and drawbacks of genetic algorithms applications to aerodynamic design are demonstrated. A numerical procedure for the aerodynamic design of transonic airfoils by means of genetic algorithms, with single-point, multipoint, and multiobjective optimization capabilities, is presented. In the ® rst part, an investigation on the relative ef® ciency of different genetic operators combinations is carried out on an aerodynamic inverse design problem. It is shown how an appropriate tuning of the algorithm can provide improved performances, better adaption to design space size and topology, and variables cross correlation. In the second part, the multiobjective approach to design is introduced. The problem of the optimization of the drag rise characteristics of a transonic airfoil is addressed and dealt with using a single point, a multipoint, and a multiobjective approach. A comparison between the results obtained using the three different strategies is ® nally established, showing the advantages of multiobjective optimization.

Boundary Layer Development in Axial Compressors and Turbines: Part 2 of 4—Compressors

Abstract: This is Part Two of a four-part paper. It begins with Section 6.0 and continues to describe the comprehensive experiments and computational analyses that have led to a detailed picture of boundary layer development on airfoil surfaces in multistage turbomachinery. In this part, we present the experimental evidence used to construct the composite picture for compressors given in the discussion in Section 5.0 of Part 1. We show the data from the surface hot-film gages and the boundary layer surveys, give a thorough interpretation for the baseline operating condition, and then show how this picture changes with variations in Reynolds number, airfoil loading, frequency of occurrence of wakes and wake turbulence intensity. Detailed flow features are described using raw time traces. The use of rods to simulate airfoil wakes is also evaluated.

Boundary layer and flow control by periodic addition of momentum

Abstract: Oscillatory addition of momentum without the addition of mass flow is very effective in delaying separation, particularly from lifting surfaces. It is much more robust than the steady blowing traditionally used for this purpose. Experiments carried out on different airfoils revealed that this flow depends on many parameters such as: the location of the blowing slot, the steady and oscillatory momentum coefficients (if oscillatory blowing is used), the frequency of the imposed oscillations and the shape and incidence of the airfoils. The incremental improvements in the airfoil characteristics are insensitive to changes in Reynolds number provided the latter is sufficiently large. Preliminary results suggest that the improvements in the airfoil performance are not hindered by compressibility at subsonic speeds or by sweep. Furthermore the method can be applied to diffusers and thus used for thrust augmentation and vectoring. It can also be applied to helicopter rotors and alleviate the effects of dynamic stall, some preliminary results on pitching airfoil are shown. The oscillatory blowing and suction used most often can be replaced by other means providing the appropriate oscillatory component of the momentum coefficient at the right frequency. The method is therefore independent of the device producing the oscillations. It became clear that a delay of separation is a distinctly different task than the promotion of .reattachment yet both are important in operating an airfoil or a flap near its natural stall. Some examples, showing the instantaneous (or phase locked to the disturbance and ensemble-averaged) pressure distributions and voiticity distributions over a flap will be given. The integration of geometrical design with the imposed forced oscillations providing the maximum pressure recovery over the shortest possible distance is now under consideration.

Comparative Results From a CFD Challenge Over a 2D Three-Element High-Lift Airfoil

Abstract: A high-lift workshop was held in May of 1993 at NASA Langley Research Center. A major part of the workshop centered on a blind test of various computational fluid dynamics (CFD) methods in which the flow about a two-dimensional (2D) three-element airfoil was computed without prior knowledge of the experimental data. The results of this ''blind'' test revealed: 1. The Reynolds Averaged Navier-Stokes (RANS) methods generally showed less variability among codes than did potential/Euler solvers coupled with boundary-layer solution techniques. However, some of the coupled methods still provided excellent predictions. 2. Drag prediction using coupled methods agreed more closely with experiment than the RANS methods. Lift was more accurately predicted than drag for both methods. 3. The CFD methods did well in predicting lift and drag changes due to changes in Reynolds number, however, they did not perform as well when predicting lift and drag increments due to changing flap gap. 4. Pressures and skin friction compared favorably with experiment for most of the codes. 5. There was a large variability in most of the velocity profile predictions. Computational results predict a stronger slat wake than measured suggesting a missing component in turbulence modeling, perhaps curvature effects.

Panel damped hybrid blade

Abstract: A fan blade includes a metal airfoil having first and second opposite sides extending radially between a root and a tip, and axially between a leading edge and a trailing edge. The airfoil further includes a pocket disposed in the first side having an elastomeric filler bonded therein. A panel is bonded to the filler along the pocket for allowing differential movement therebetween for damping vibratory response of the airfoil.

Effects of Surface Roughness on Heat Transfer and Aerodynamic Performance of Turbine Airfoils

Abstract: Aerodynamic flow path losses and turbine airfoil gas side heat transfer are strongly affected by the gas side surface finish. For high aero efficiencies and reduced cooling requirements, airfoil designs dictate extensive surface finishing processes to produce smooth surfaces and enhance engine performance. The achievement of these requirements incurs additional manufacturing finishing costs over less strict requirements. The present work quantifies the heat transfer (and aero) performance differences of three cast airfoils with varying degrees of surface finish treatment. An airfoil, that was grit blast and Codep coated, produced an average roughness of 2.33 {micro}m, one that was grit blast, tumbled, and aluminide coated produced 1.03 {micro}m roughness, and another that received further postcoating polishing produced 0.81 {micro}m roughness. Local heat transfer coefficients were experimentally measured with a transient technique in a linear cascade with a wide range of flow Reynolds numbers covering typical engine conditions. The measured heat transfer coefficients were used with a rough surface Reynolds analogy to determine the local skin friction coefficients, from which the drag forces and aero efficiencies were calculated. Results show that tumbling and polishing reduce the average roughness and improve performance. The largest differences are observed from the tumbling process, with smallermore » improvements realized from polishing.« less

Study of Adaptive Shape Airfoils at Low Reynolds Number in Oscillatory Flows

Abstract: Microaerial vehicles with characteristic lengths under 15 cm, flight speeds of 32-64 km/h, and specific payload and endurance needs are potentially useful for many military and civilian applications. The combination of small dimensions and modest flight speed results in Reynolds numbers ranging between 10 4 and 10 5 . Traditional rigid airfoil shapes experience substantial degradation in performance (specifically, the lift-to-drag ratio) as the Reynolds number falls through this range. Thus, even ordinary variations in wind speed can cause unwanted changes in behavior. In this study, rudimentary adaptive airfoils, which change their shape in response to changes in velocity, are examined for potential applications in this arena.

A Feasibility Study To Control Airfoil Shape Using THUNDER

Abstract: The objective of this study was to assess the capabilities of a new out-of-plane displacement piezoelectric actuator called thin-layer composite-unimorph ferroelectric driver and sensor (THUNDER) to alter the upper surface geometry of a subscale airfoil to enhance performance under aerodynamic loading. Sixty test conditions, consisting of combinations of five angles of attack, four dc applied voltages, and three tunnel velocities, were studied in a tabletop wind tunnel. Results indicated that larger magnitudes of applied voltage produced larger wafer displacements. Wind-off displacements were also consistently larger than wind-on. Higher velocities produced larger displacements than lower velocities because of increased upper surface suction. Increased suction also resulted in larger displacements at higher angles of attack. Creep and hysteresis of the wafer, which were identified at each test condition, contributed to larger negative displacements for all negative applied voltages and larger positive displacements for the smaller positive applied voltage (+102 V). An elastic membrane used to hold the wafer to the upper surface hindered displacements at the larger positive applied voltage (+170 V). Both creep and hysteresis appeared bounded based on the analysis of several displacement cycles. These results show that THUNDER can be used to alter the camber of a small airfoil under aerodynamic loads.

Spanwise fan diffusion hole airfoil

Abstract: A turbine airfoil includes a leading edge, a trailing edge, and a root and tip spaced apart along a span axis. First and second airfoil sides extend therebetween. A cooling circuit is disposed between the sides for channeling a cooling fluid. A plurality of diffusion fan holes are spaced apart along the span axis in the airfoil first side, with each fan hole increasing in flow area between an inlet at the cooling circuit and an outlet on the airfoil first side disposed coaxially about a centerline fan axis. The fan axis is inclined at an acute span angle, with the outlet being greater in span height than the inlet, and substantially equal in width for increasing coverage of the outlets and film cooling air therefrom along the span axis.

Crack arresting rotor blade

Abstract: A rotor blade includes a dovetail and an airfoil joined thereto. The airfoil includes first and second spaced apart sides joined together laterally at opposite leading and trailing edges, and spanwise at a root and opposite tip. A serpentine cooling circuit extends inside the airfoil for channeling air therethrough for cooling the blade. The serpentine circuit includes first and second passes and a first bend therebetween for firstly receiving the cooling air in turn from the dovetail. A tip circuit is disposed between the tip and the serpentine circuit at the first bend for separating the tip from the first bend and providing cooling thereof near the trailing edge.

Influence of camber on sound generation by airfoils interacting with high-frequency gusts

Abstract: A theoretical model is developed for the sound generated when a convected disturbance encounters a cambered airfoil at non-zero angle of attack. The model is a generalization of a previous theory for a flat-plate airfoil, and is based on a linearization of the Euler equations about the steady, subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, are considered. The airfoil camber and incidence angle are restricted so that the mean flow past the airfoil is a small perturbation to a uniform flow. The singular perturbation analysis retains the asymptotic regions present in the case of a flat-plate airfoil: local regions, which scale on the gust wavelength, at the airfoil leading and trailing edges; a 'transition' region behind the airfoil which is similar to the transition zone between illuminated and shadow regions in optical problems; and an outer region, far away from the airfoil edges and wake, in which the solution has a geometric-acoustics form. For the cambered airfoil, an additional asymptotic region in the form of an acoustic boundary layer adjacent to the airfoil surface is required in order to account for surface curvature effects. Parametric calculations are presented which illustrate that, like incidence angle, moderate amounts of airfoil camber can significantly affect the sound field produced by airfoil-gust interactions. Most importantly, the amount of radiated sound power is found to correlate very well with a single aerodynamic loading parameter, α eff , which is an effective mean-flow incidence angle for the airfoil leading edge.

Low Reynolds Number Airfoils for Small Horizontal Axis Wind Thrbines

Abstract: To facilitate the airfoil selection process for small horizontal-axis wind turbines, an extensive database of low Reynolds number airfoils has been generated. The database, which consists of lift and drag data, was obtained from experiments conducted in the same wind tunnel testing facility. Experiments with simulated leading-edge roughness were also performed to model the effect of blade erosion and the accumulation of roughness elements, such as insect debris, on airfoil performance. Based on the lift curves and drag polars, guidelines that should be useful in selecting appropriate airfoils for particular blade designs are given. Some of these guidelines are also applicable to larger HAWTs.

An evaluation of an empirical model for stall delay due to rotation for HAWTS

Abstract: The objective of this study was to evaluate the Corrigan and Schillings stall delay model for predicting rotor performance for horizontal axis wind turbines. Two-dimensional (2D) wind tunnel characteristics with and without stall delay were used in the computer program PROP93 to predict performance for the NREL Combined Experiment Rotor (CER) and a lower solidity commercial machine. For the CER, predictions were made with a constant-chord/twisted blade and a hypothetical tapered/twisted blade. Results for the constant-chord/twisted blade were compared with CER data. Predicted performance using this empirical stall-delay method provided significant increases in peak power over 2D post-stall airfoil characteristics. The predicted peak power increase due to stall delay for the CER was found to be quite large (20% to 30%) as a result of its high blade solidity. For a more typical, lower-solidity commercial blade the predicted peak power increase was 15% to 20%. As described in the paper, correlation with test data was problematic due to factors not related to the stall-delay model.

Gurney Flap Scaling for Optimum Lift-to-Drag Ratio

Abstract: This note aims at providing evidence that there exists a flow-based scaling for the Gurney flap heights that yield an increase in lift-to-drag performance compared with the baseline airfoil at the same angle of attack (beneficial Gurney flaps). The results presented here, support this statement and further suggest that the boundary-layer thickness δ, measured at the trailing edge on the pressure side of the baseline airfoil, is not only an appropriate flow-based normalization for the flap height but is also a proper order of magnitude for the flap height providing the largest increase in the lift-to-drag ratio (optimum Gurney flap)

Adaptive Control of Aeroelastic Instabilities in Transonic Flow and Its Scaling

Abstract: A two-dimensional aeroservoelastic study in the time domain is described. The model, based on exact inviscid aerodynamics, correctly represents the large amplitude motions and the associated strong shock dynamics in the transonic regime. The aeroservoelastic system consists of a two-degree-of-freedom airfoil with a trailing-edge control surface. Active e utter suppression in the presence of nonlinear aeroelastic phenomena is achieved using e rst-order actuator dynamics and a digital adaptive controller. A relation between actuator dynamics and limits on the e ap dee ection angle to guarantee the effectiveness of the adaptive controller is illustrated by the results. Hingemomentcalculationsandpowerrequirementsfore uttersuppressionarealsocarriedout. Aeroelasticscaling requirements for the governing parameters, including actuator moment and control power, are established.