SITIS Topic Details |
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| Proposals Accepted: | |
| Program: | SBIR |
| Topic Number: | A10-148 (Army) |
| Title: | Efficient Lifting Surface Method for Rotorcraft Analysis | Research & Technical Areas: | Air Platform |
| Acquisition Program: | PEO Aviation | Objective: | Develop an efficient lifting surface method to be incorporated into a rotorcraft comprehensive analysis framework for effective prediction of rotor aerodynamic loading, performance and stability. The method would be more accurate than lifting line methods, yet significantly less computationally intensive than CFD methods.
| Description: | Computational predictive capabilities are critical for all phases of rotorcraft engineering, research and development. Because of the conflicting requirements for accuracy and computational efficiency, a range of rotorcraft modeling and simulation methods are used by today’s researchers and designers to satisfy these needs. Traditional rotorcraft comprehensive codes, e.g., RCAS (Ref.1) and CAMRAD II (Ref. 2) currently in wide use are based on semi-empirical lifting line methods. Considerable attention is now being focused on coupling such codes with CFD methods to accurately address the most complex aspects of rotorcraft aerodynamic phenomena. These coupled CFD methods demonstrated phenomenal improvement in predictive accuracy for both steady and maneuvering flight (Refs. 3, 4). At least a large part of this apparent improvement is tied to the overly simplistic assumptions in the lifting-line methods. Although these methods are computationally efficient, they lack even simple 3-D flow effects and are, therefore, unable to account for the aerodynamics of advanced planform and tip-shape effects, cambered airfoils, and the aerodynamics of low aspect ratio wing and tail surfaces. In the fixed-wing arena lifting surface methods have been extensively used to model these effects accurately (Refs. 5-11). Lifting surface methods can model the 3-D flow effects leading to accurate prediction of not only lift but also pitch moment, thereby bridging the gap between simple lifting line theory and large CFD methods. This capability is crucial for rotorcraft applications as it drives control loads predictions. However, within the spectrum of rotorcraft analysis tools, such intermediate lifting surface methods are conspicuous by their absence. There have been some rotorcraft developments (Refs. 12-16), but their benefits have been largely neglected by the rotorcraft community. This topic is aimed at developing a suitable lifting surface method, leveraging the most appropriate existing theory, to provide useful and cost effective software that may be integrated with existing rotorcraft comprehensive codes.
The methods of interest will likely be linear methods for maximum versatility and simplicity, probably vortex lattice methods modeling the mean surface of the wing or rotor blade. Panel methods may be considered but are not necessary. Both rotating and fixed lifting surfaces, e.g., rotor blades and wing/tail, should be addressed. Both steady and unsteady applications are of interest, thus some form of the doublet lattice method is probably appropriate. Ability to predict the inviscid aerodynamic lift, drag (induced), and moment characteristics must be demonstrated. Complex nonlinear effects, typical of rotorcraft aerodynamics, e.g., shocks, separation and stall effects, and effects of nonlinear wake geometry (self-induced free wake convection) are considered beyond the scope of this topic. Unsteady aerodynamics should be included, preferably in a state space formulation to enable efficient coupling with structural models for stability analysis (linear eigenanalysis methods). The topic will include basic tools to define and model typical wings and rotor blades having arbitrary geometries, tools to extract resultant blade loading, section aerodynamic properties, etc., and the development of software code in modular form that may be incorporated into a comprehensive analysis.
| PHASE I: Define appropriate theory basis for the intended code and extend/develop as appropriate for rotorcraft applications. Design an applicable software architecture including proposed interface with a typical comprehensive code, e.g., RCAS. Code a prototype version of a portion of the lifting surface method for a rotating component (rotor blade) and demonstrate sample results for a representative configuration.
| PHASE II: Complete development of all theory required. Refine the preliminary design and complete the detailed design of the lifting surface software. Implement the software design including software testing and demonstration for a representative suite of test problems. Perform a detailed analysis and incorporate the full lifting surface code into a rotorcraft comprehensive code. Develop documentation including theory, user, software design manuals, and sample problems.
| PHASE III: Develop and refine the lifting surface model into a stand-alone module for application to the rotorcraft design process. This should be programmed to be used either as a stand-alone tool or as a module under a python-based software framework. Initially the module may be coupled into the US Army's RCAS comprehensive code and the future high-performance high fidelity analysis tool, HI-ARMS, to provide alternative levels of fidelity. The industry is also moving towards this type of software framework and the lifting surface module will have a unique position in industry's design tools. Here, advanced design methodology will be equally applicable to military and civilian vehicles, increasing design cycle effectiveness and ultimately reducing development and operating costs and improving vehicle mission effectiveness.
| References: | 1. Saberi, H, Khoslahjeh, M, Ormiston, R. A., and Rutkowski, M. J., ‘Overview of RCAS and Application to Advanced Rotorcraft Problems,’American Helicopter Society 4th Decennial Specialists‚ Conference on Aeromechanics, San Francisco, CA, January 2004. 2. Johnson, W., “Rotorcraft Aerodynamic Models for a Comprehensive Analysis,” 54th Annual Forum, American Helicopter Society, Alexandria, VA, May 1998 3. Potsdam, M., Yeo, H. and Johnson, W., ‘Rotor Airloads Predictions Using Loose Aerodynamic/Structural Coupling’, American Helicopter Society 60th Annual Forum, Baltimore MD, June 2004. 4. Bhagwat, M. J., Ormiston, R. A., Saberi, H. A. and Xin, H., “Application of CFD/CSD Coupling for Analysis of Rotorcraft Airloads and Blade Loads in Maneuvering Flight,” American Helicopter Society 63rd Annual Forum, Virginia Beach, VA, May 1-3, 2007. 5. Lan, C.E., “A Quasi-Vortex-Lattice Method in Thin Wing Theory”, Journal of Aircraft, Vol.11, No. 9, September 1974, pp. 518-527. 6. Kalman, T.P., Rodden, W.P., and Giesing, J., “Application of the Doublet-Lattice Method to Nonplanar Configurations in Subsonic Flow,” Journal of Aircraft, Vol. 8, No. 6, June 1971, pp. 406-415. 7. Kocurek, J.D., and Tangler, J.L. "A Prescribed Wake Lifting Surface Hover Performance Analysis." Journal of the American Helicopter Society, 22:1 (January 1977). 8. Margason, R.J., and Lamar, J.E., “Vortex-Lattice FORTRAN Program for Estimating Subsonic Aerodynamic Characteristics of Complex Planforms,” NASA TN D-6142, 1971 9. Hough, Gary R., “Remarks on Vortex-Lattice Methods,” Journal of Aircraft, Vol. 10, No. 5, May 1973, pp. 314-317. 10. Albano, E., and Rodden, W.P., “A Doublet-Lattice Method for Calculating Lift Distributions on Oscillating Surfaces in Subsonic Flows,” AIAA J., Vol. 7, No. 2, February 1969, pp. 279-285; errata AIAA J., Vol. 7, No. 11, November 1969, p. 2192. 11. Carmichael, R.L., and Erickson, L.L., "PAN AIR - A Higher Order Panel Method for Predicting Subsonic or Supersonic Linear Potential Flows About Arbitrary Configurations," AIAA Paper No. 81-1255, June 1981. 12. Ashby, D.L., Dudley, M.R., Iguchi, S.K., Browne, L., and Katz, J., “Potential Flow Theory and Operation Guide for the Panel Code PMARC,” NASA TM 102851, Jan. 1991. 13. Quackenbush, T.R.; Bliss, D.B.; and Wachspress, D.A. "New Free-Wake Analysis of Rotorcraft Hover Performance Using Influence Coefficients." Journal of Aircraft, 26:12 (December 1989). 14. Runyan, H.L., and Tai, H. "Application of a Lifting Surface Theory for a Helicopter in Forward Flight." Vertica, 10:3/4 (1986). 15. Shenoy, K.R., and Gray, R.B. "Iterative Lifting Surface Method for Thick Bladed Hovering Helicopter Rotors." Journal of Aircraft, 18:6 (June 1981). 16. Summa, J.M., and Clark, D.R. "A Lifting-Surface Method for Hover/Climb Airloads." American Helicopter Society 35th Annual Forum, Washington, D.C., May 1979. |
| Keywords: | Lifting surface theory, vortex lattice method, rotorcraft aerodynamics, comprehensive analysis |
Questions and Answers: |
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