Incompressible Potential Flow. Panel Methods (3)

Transcription

1 Incompressible Potential Flow Panel Methods (3)

2 Outline Some Potential Theory Derivation of the Integral Equation for the Potential Classic Panel Method Program PANEL Subsonic Airfoil Aerodynamics Issues in the Problem formulation for 3D flow over aircraft Example applications of panel methods Using Panel Methods Advanced panel methods

3 Issues in the Problem formulation for 3D flow over aircraft The proper treatment of wing tips The treatment of the wake The fuselage aft of the wing No leakage in the panel model representation of the surface The outward surface normal is oriented in the proper direction All surface are properly enclosed Wakes are properly specified Handled automatically Precisely specified by the user

4 Wing-body-tail configuration panel scheme with wakes

5 Example applications of panel methods Evaluations of aerodynamic characteristics for aircraft configuration Effect of wing-tunnel walls America s Cup designs An example in some detail Boeing Impact of CFD on design of Boeing

6 Evaluating the effect of the space shuttle on the Boeing 747

7 Lift coefficients for a generic fight aircraft configuration

8 Lift coefficients for the F/A-18

9 Effect of wing-tunnel walls on the distribution on the upper surface

10 America s Cup designs Hull and keel design Free surface design

11 Background An example in some detail Boeing Modifications of to configuration The design of a new high lift system. The design tool: PAN AIR

12 Objective An understanding of the wing flow-field for two different takeoff flap settings Flap 15: 2900 panels Flap 1 : 1750 panels The panel representation of the with 15 flap deflection

13 Modeling The computational models used 1750 panels for flaps 1 and 2900 panels for flaps 15. Inboard wing leading edge and nacelle details

14 Modeling The triple slotted flap was modeled as a single element flap. The gap between the forward vane and main flap is closed, and the gap between the main and aft flap is very small. Comparison of actual and computational wing geometry for the flaps 1 case Actual and computational trailing edge geometry for the flaps 15 case

15 Modeling Spanwise discontinuity Spanwise discontinuity details requiring modeling for flaps 1 case

16 Modeling The nacelle model The specification of the inlet flow at the engine face A model of the strut wake, The outer bypass air plume and the primary wake from the inner hot gas jet.

17 Results: Spanwise distribution of lift coefficient Flaps 1 case

18 Flaps 15 case In both cases the jig shape and flight shape including aeroelastic deformation are included. In both cases the shape including the deformation under load shows much better agreement with flight and wind tunnel data. Notice the loss of lift on the wing at the nacelle station,and the decrease in lift outboard of the trailing edge flap location.

19 Results The change in section lift coefficient with angle of attack flaps 1 case

20 Flap 15 case The agreement between PAN AIR and flight test is better for the flaps 1 case. Viscous effects are becoming important for the flaps 15 case.

21 Results: pressure distributions Flap 1 case Flap 15 case Comparison of pressure distributions between flight and computations

22 Comments on results of pressure distributions The flaps 1 case agreement is generally good. Calculations are presented for both the actual angle of attack, and the angle of attack which matches the lift coefficient. The flaps 15 case starts to show the problems that arise from these simplifications. This is a good example of the use of a panel method.

23 Impact of CFD on the design of Background Boeing Boeing 737 series might not have remained in production beyond the mid-1980s, if not for the installation of a modern, large diameter, high bypass ratio turbofan engine. Competitive pressures from MD-82 New federal regulations demanded significant noise reduction The installation of a modern turbofan engine could meet the need, if it could be accomplished without incurring an excessive increase in interference drag, weight, or cost.

24 Boeing CFM56-3 Turbofan

25 The Conventional wisdom To avoid the interference drag would have required lengthening the landing gear to provide proper ground clearance. Increasing the landing gear length would result in extra weight and excessive costs to modify the aircraft structure.

26 Challenge Finding the solution, which allowed a much larger diameter engine to fit under the wing without increasing the main landing gear length.

27 The need, the opportunity, and technology were available to provide a solution to this challenge

28 Understanding the problem using CA The numerical simulation revealed that the source of the interference drag is induce drag or vortex drag caused by a change in wing span loading due to the presence of the nacelle and strut. The wind tunnel had been unable to do it. Clean wing c l Full configuration (nacelle and pylons) spanwise

29 Resolving the problem Redesigning the nacelle and strut to prevent adverse impact to spanwise load distribution of the wing. Properly contoured nacelle and strut design could and was done much more effectively with computational methods than with the wind tunnel because computational method automatically produce finely detail pressure on all wing, strut, and nacelle surface.

30 Impart of Computational Aerodynamics The knowledge provided by CFD made possible the very successful major derivative to original /400/500/600/700/800 This story showed that the impact of CFD contribution to most successful commercial jet airplane series in history.

31 As a replacement for s, the forward-looking offered more seats, better performance and fuel economy, and much lower noise.

32 The offers the revenue opportunities of additional cargo capacity and more seats, as well as the operating savings of crew and engine commonality and lower seat-mile costs.

33 Although it has the largest model designator of its generation, the is actually smaller than either the or the

34 The smallest member of the Next-Generation 737 airplane family, is equivalent in size to the , and provides seating for 110 to 132 passengers.

35 Equivalent in size to the , the has a new larger wing, a larger tail, and new engines that ensure 737 market leadership well into the 21st-century.

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37 The largest of the Next-Generation 737 models, is a derivative of the Boeing

38 Research Opportunity for Large Transport One of the recent research issues listed in China Aeronautical Science Foundation: reducing the interfere drag caused by the nacelle and strut.

39 Using Panel Methods Common sense rules for panels Vary the size of panels smoothly Panel placement and variation of panel size affect the quality of the solution. Extreme sensitivity of the solution to the panel layout is an indication of an improperly posed problem. If this happens, the user should investigate the problem thoroughly. Concentrate panels where the flowfield and/or geometry is changing rapidly.

40 Cautions You must use the results as a guide to help you develop your own judgment. To get the most from the methods, you are required to have An understanding of aerodynamics that provides an intuitive expectation of the types of results An appreciation of how to relate your idealization to the real flow What a Panel Method Can't Do Panel methods are inviscid solutions You will not capture viscous effects except via user modeling by changing the geometry. Solutions are invalid as soon as the flow develops local supersonic zones

41 Advanced Panel Methods What is a Higher Order Panel Method? using singularity distributions that are not constant on the panel using panels which are non-planar Why is Higher Order Panel Method needed? Be crucial in obtaining accurate solutions for the Prandtl-Glauert Equation at supersonic speeds. Good results can be obtained using far fewer panels with higher order methods.

42 Today s Standard Programs A brief review Panel methods are widely used in the aircraft industry, and have been for a long time. All the new professionally-developed codes work well. The selection of a specific code will likely be based on non-technical considerations.

43 Today s Standard Programs Product Codes PAN AIR VSAERO QUADPAN Version of the Hess Codes Woodward PMARC CMARC

44 PANAIR Boeing-developed code, funded by a variety of government agencies. It uses higher order panels, and is both subsonic and supersonic. It s relatively expensive and difficult to run. To effectively use the code good pre- and postprocessing systems must be available.

45 VSAERO AMI developed (Analytical Mechanics Inc., Frank Dvorak and Brian Maskew). It uses low order panels and is subsonic only. It handles general geometries, and includes options to treat viscous effects and vortex flows. Expensive

46 Example of application using VSAERO

47 Panel Model of MD-11 in Ground Effect During Take Off Rotation

48 QUADPAN Lockheed-developed, and possibly developed at some government labs. Not widely used by industry outside of Lockheed. This is probably because of availability.

49 Version of the Hess Codes Further developments of the team at Douglas now led by Hess. Douglas uses this code exclusively. Douglas developed numerous versions under various government contracts

50 Woodward Woodward was a pioneer panel method developer Woodward went into business and continued to develop codes. USSAERO developed under NASA contract treats both supersonic and subsonic flow

51 PMARC The newest panel method code developed at NASA Ames The code is a lower order panel method, and can simulate steady as well as unsteady flow. The wake position can be obtained as part of the solution. Providing an extremely flexible method to simulate a wide range of very general geometries simulation of high lift systems jet exhausts for VSTOL aircraft

52 Example of application: Morphing Aircraft

53 control effectiveness contours

54 Comparison of Some Major Panel Method Programs Early Codes

55 Comparison of Some Major Panel Method Programs Advanced Methods

56 Comparison of Some Major Panel Method Programs Production Codes