A High-efficiency Trim Method for CFD Numerical Calculation of Helicopter Rotors

다국어 초록 (Multilingual Abstract)

In order to resolve the trimming difficulty in rotor CFD calculations, a high-efficiency and improved “delta trim method” is established to compute the blade control settings that are necessary to identify the blade motion. In this method, a simplified model which combines the blade element theory and different inflow models is employed to calculate the control settings according to the target aerodynamic forces, then it is coupled into a CFD solver with unsteady Navier-Stokes equations by the delta methodology, which makes the control settings and aerodynamics calculated and updated in the meantime at every trim cycle. Different from the previous work, the current research combines the inflow model based on prescribed wake theory. Using the method established, the control settings and aerodynamic characteristics of Helishape 7A, AH-1G and Caradonna-Tung rotors are calculated. The influence of different inflow models on trimming calculations is analyzed and the computational efficiency of the current “delta trim method” is compared with that of the “CFD-based trim method”. Furthermore, for the sake of improving the calculation efficiency, a novel acceleration factor method is introduced to accelerate the trimming process. From the numerical cases, it is demonstrated that the current “delta trim method” has higher computational efficiency than “CFD-based trim method” in both hover and forward flight, and up to 70% of the amount of calculation can be saved by current “delta trim method” which turns out to be satisfactory for engineering applications. In addition, the proposed acceleration factor shows a good ability to accelerate the trim procedure, and the prescribed wake inflow model is always of better stability than other simple inflow models whether the acceleration factor is utilized in trimming calculations.

목차 (Table of Contents)

• Abstract
• 1. Introduction
• 2. Numerical methods
• 3. Calculation results and analysis
• 4. Conclusions
• References

참고문헌 (Reference)

1 Baldwin, B. S, "Thin Layer Approximation And Algebraic Model for Separated Turbulent Flows" 1978

2 Cross, J. F, "Tabulation of Data from the Tip Aerodynamics and Acoustics Test" 1990

3 Biava, M, "Single Blade Computations of Helicopter Rotors in Forward Flight" 2003

4 Ashish Bagai, "Rotor free-wake modeling using a pseudoimplicit relaxation algorithm" American Institute of Aeronautics and Astronautics (AIAA) 32 (32): 1276-1285, 1995

5 Zhong Yang, "Recent Improvements to a Hybrid Method for Rotors in Forward Flight" American Institute of Aeronautics and Astronautics (AIAA) 39 (39): 804-812, 2002

6 Allen, C. B, "Parallel Flow-Solver and Mesh Motion Scheme for Forward Flight Rotor Simulation" 2006

7 Lohner, R, "Overlapping Unstructured Grid" 2001

8 Chiu, I. T, "On Automating Domain Connectivity for Overset Grids" 1995

9 Chung, K. H, "Numerical Predictions of Rotorcraft Unsteady Air-Loadings and BVI Noise by Using A Time-Marching Free-Wake Acoustic Analogy" 2005

10 Kim, J. W, "Euler and Navier-Stokes Simulations of Helicopter Rotor Blade in Forward Flight Using An Overlapped Grid Solver" 2009

11 Piergiovanni Renzoni, "EROS — a common European Euler code for the analysis of the helicopter rotor flowfield" Elsevier BV 36 (36): 437-485, 2000

12 Bagai, A, "Contributions to the Mathematical Modeling of Rotor Flowfield Using a Pseudo-Implicit Free-Wake Analysis" University of Maryland Press 1995

13 Blazek, J, "Computational Fluid Dynamics: Principles and Applications" Elsevier Ltd Press 2005

14 Bramwell, A, "Bramwell’s Helicopter Dynamics" Butterworth-Heinemann Press 2001

15 P.L Roe, "Approximate Riemann solvers, parameter vectors, and difference schemes" Elsevier BV 43 (43): 357-372, 1981

16 Lebel, G, "Aerodynamic and Dynamic Models for Rotor Load Prediction – Application to New Generation Blades" 2011

17 Leishman, J. G, "Aerodynamic Optimization of A Coaxial Proprotor" 2006

18 Jinggen Zhao, "A Viscous Vortex Particle Model for Rotor Wake and Interference Analysis" American Helicopter Society 55 (55): 12007-1200714, 2010

19 Drees, J. M, "A Theory of Airflow Through Rotors and its Application to Some Helicopter Problems" 3 (3): 79-104, 1949

20 Luo, H, "A Fast, Matrix-Free Implicit Method for Computing Low Mach Number Flows on Unstructured Grids" 14 (14): 133-157, 2000

21 Steijl, R, "A CFD Framework for Analysis of Helicopter Rotors" 2005