A NUFFT technique for flow fluctuation analysis based on the unsteady flow simulation with variable physical time stepping scheme

An analysis technique on flow fluctuation combined with Non-Uniform Fast Fourier Transform (NUFFT) is developed and presented in this paper, which is based on the unsteady flow simulation with variable physical time stepping scheme. This technique is suitable to analyze fluctuation features in an unsteady flow in both time domain and frequency domain. The developed method has been integrated in a hybrid unstructured Navier-Stokes flow solver. The buffeting flow around supercritical OAT15A airfoil and wake bursting flow around MD 30P/30N airfoil are simulated and analyzed for the validation and assessment of the presented technique. The ability and accuracy of this technique on predicting the fluctuation variables are verified by comparing the predicted results with the experimental data. The results show that the presented NUFFT flow fluctuating analysis technique achieves the balance between the computational cost and resolution requirements on the frequency spectral analysis. Under the same computational cost, this method can produce a higher resolution on spectral and expand the frequency bandwidth nearly two times compared with the uniform sample method.