| The numerical computation of unsteady aerodynamic loading and noise for rotor blade-vortex interaction(BVI) is a highly challenging subject in the field of helicopter aerodynamics and aeroacoustics. The rotor computational fluid dynamics(CFD) method, hybrid CFD method for aerodynamic and acoustic analysis of blade-vortex interaction have been investigated in this thesis and the corresponding code based on the CFD and noise prediction method in the time domain are also developed. The rotor blade interacting with both independently generated and self-generated vortices are computed and analyzed. Meanwhile, the effects of new blade tips on BVI noise are simulated. The major contributions of the author's research work are as follows:As the background of present work, the objectives of the research are firstly described. The research and development in the field of rotor CFD, hybrid CFD, as well as aerodynamics and acoustics of rotor blade-vortex interaction are briefly introduced, and the difficulties in the current research are also pointed out. In addition, the methods used in the present research are briefly brought forward.A numerical method, based on moving-overset grid technology, for predicting aerodynamic flow around helicopter rotors in hover and forward flight has been developed and the method validation is also carried out through several numerical examples on different rotors. To minimize the effects of grid on numerical results, some improved solutions are provided. Aiming at BVI noise analysis, a noise prediction method based on Farassat 1A formulation in time domain is developed. In this method, the pressure on blade surface obtained from CFD is used for the acoustic calculations.By applying the developed flowfield and noise prediction method, the deep research on mechanism of 2D airfoil-vortex interaction is performed first. On the basis, the aerodynamic and acoustic charactericstics of rotor blade interacting with independently generated vortex are studied further. The parametric effects study on parallel and oblique blade-vortex interaction and transonic BVI are also conducted. From the above studies, some new conclusions are obtained.To improve computational efficiency noticeably, two new sets of single-blade based hybrid CFD methods combined with wake analysis, which called HCM1 and HCM2, are developed. The CFD computation and rotor wake analysis are conducted parallel to reduce computational time further. By this method, several hover and forward flight cases on Caradonna-Tung and Helishpae 7A rotors are performed. The good agreements of the loadings on blade surface with available measured data demonstrate the validation of the method. Also, the CPU time required for different computation runs are compared, and the results show that the present hybrid method is much more superior to conventional CFD method in time cost. In addition, the comparisons between the two hybrid methods are also made, and the distinctive features of two methods are pointed out.By employing the developed hybrid CFD method and rotor trim analysis, a new model for studying the rotor blade interacting with self-generated vortex is developed. By this method, the aerodynamic and acoustic characteristics of blade-vortex interaction for AH-1/OLS rotor are studied deeply. Furthermore, the effects of attack angle of tip-path-plane, thrust coefficient, advance ratio and tip Mach number on blade-vortex interaction characteristics are analyzed. And some meaningful conclusions for rotor design are drawn.Finally, the noise calculations of the rotor with such new tips as backward sweep, forward sweep, tapered and anhedral shapes at BVI conditions are performed. And the influence of their changing interaction types on the aerodynamics and acoustics of BVI are investigated.
|
PDF Full Text Request