Modeling On Time-Accurate Free Wake Method And Investigation On Aerodynamic Characteristics Of Rotor And Tiltrotor

In this paper, a new time-accurate rotor free wake method has been developed, and using the method, vortical wake and aerodynamic characteristics of rotor and tilting rotor are calculated and analyzed. As the same time, the aerodynamic experiments for the tilting rotor are performed. The major contributions of the author's research work are as follows:As the background of the work, the research and development in the field of the rotor free wake method, the aerodynamic characteristics of rotor and tiltrotor are described in Chapter 1. The difficulties in the current rotor free wake method research are pointed out. And the importance of simulating aerodynamic characteristics of rotor and tiltrotor by the wake method is emphasized. Moreover, the present work is briefly introduced.In Chapter 2, a different algebraic vortex model is developed based on the Vatistas formula, and the expression of vortex core radius is given under the consideration of vortex diffusion. As numerical examples, the induced velocity distributions of the vortex ring and vortex tube are calculated to indicate the effects of the vortex model on the calculated results of induced velocity. Then the calculated inflows for rotor are compared with the available experimental data to show the validity of the present vortex model.A general method used to deduce multi-step differencing scheme is given in Chapter 3, and based upon the method, a new 2-step 2-order accurate predictor-corrector with backward difference algorithm—named"D2PC"is deduced. Both the stability and accuracy of the"D2PC"numerical wake solution algorithm are examined. By comparisons with the critical 1-step and 3-step difference algorithms, the validity of"D2PC"algorithm is demonstrated. Numerical errors associated with the wake discretization are analyzed. In order to increase the accuracy of the solution for rotor wake, the discrete approximations of vortex governing equations using"D2PC"algorithm are modified and improved.In Chapter 4, based on the extended Euler dynamic equations, the rigid blade flap dynamic equations for rotor in steady flight, angular motion and tilting motion are deduced. The blade is simulated by the Weissinger-L lift-surfacing model, and the methods for determining the blade bound vorticity strength, tip vortex strength and release position are given.In Chapter 5, a trimming model is modified for fitting the time-stepping wake calculation. Combined the trimming model with models of Chapter 2, 3 and 4, a new time-accurate free wake method is developed for the calculation on vortical wake and aerodynamic characteristic of rotor in steady flight, angular motion and tilting motion.In Chapter 6, by the comparisons of calculated results with experimental results for some numerical examples on wake geometries, inflows, induced velocities, aerodynamic responses, the present time-accurate free wake method is validated. Using the method, time-average aerodynamic characteristics on the wake geometry, inflow and induced velocity of rotor are calculated and analyzed. Then the rotor aerodynamic responses with abrupt increase of collective pitch have been calculated. Additionally, the vortical wake geometry and inflow distribution with rotor angular motion have been analyzed. Some new conclusions are obtained.Based on the tiltrotor test rig of Nanjing University of Aeronautics and Astronautics, experimental investigations for rotor and tilting rotor have been carried out in Chapter 7. The aerodynamic characteristics of fixed rotor are tested for different rotor radius and collective pitch. Then aerodynamic characteristic tests of tilting rotor for different rotor radius, collective pitch and tilting rate have been performed. And the comparisons between experimental results and calculated results by the present method are made.In Chapter 8, the wake geometries of tilting rotor for different operating conditions are calculated and analyzed, and analysis on the aerodynamic forces and flapping responses for rotor during tilting motion has been performed. Some new conclusions are presented.