跨声风扇周向畸变流动的谐波平衡法计算

Numerical Simulation of Transonic Fan Under Circumferential Inlet Distortion Using Harmonic Balance Method

研究了采用"相位延迟"边界条件的谐波平衡法用于周向进气畸变计算的可行性及其计算效率,考虑了进气总压畸变形式为正弦波和方波的两种情况。对于正弦波形式的进气总压畸变采用较少阶数的谐波计算就可得到和双时间推进法相近的计算结果,计算速度最大可以提高48倍。对于方波形式的进气畸变,则需要采用更多阶数的谐波计算才能还原得到较准确的非定常流场,计算速度提高了7倍。算例表明,谐波平衡法可以有效的应用于跨声风扇周向进气畸变的非定常计算中,同时大幅提高计算速度。

Simulating the unsteady flow of transonic fan under circumferential inlet distortion using conventional dual time stepping method would need multiple blade passages or the whole annulus in order to apply the direct periodic condition.Also,the initial transients of the solution cost most of the computation time to decay until it reaches a periodic steady state.This makes unsteady solutions extremely time consuming and hampers its application in fan blading design process.A fast calculation method is needed to estimate the impact of the circumferential inlet distortion on the fan aerodynamic performance.Therefore,the computation feasibility and the computation speed for the unsteady calculation of the fan under circumferential inlet distortion using harmonic balance method which adopts the phase shift condition were studied.Both the sine wave form and the square wave form inlet total pressure distortion were considered.For the sine wave form inlet distortion,only a small numbers of harmonics were needed to obtain comparable results to the dual time stepping method and a maximum factor of 48 speed-up could be achieved.As for the square wave form inlet distortion,more harmonics should be adopted to get accurate results and only a factor of 7 speed-up was achieved.The results demonstrate that the harmonic balance method can apply to the unsteady calculation of transonic fan under circumferential inlet distortion effectively and reduce the computation time significantly.