Investigation of wall pressure fluctuations induced by turbulent boundary layer flow with pressure gradients

Kurzfassung

Wall pressure fluctuations induced by turbulent boundary layer flow is one major source of cabin noise. Not only the pressure fluctuation magnitude but also the spatial and temporal properties of the fluctuations are relevant for the resulting surface vibration and the noise radiated into the cabin. The one- and two-point properties of the wall pressure fluctuations are studied experimentally and numerically in thesis thesis. The wall pressure fluctuations beneath a turbulent boundary layer with zero and non-zero pressure gradients were measured at a flat plate configuration in the Aeroacoustic Wind Tunnel Braunschweig. The fluctuating pressure was measured by an L-shaped array of subminiature pressure transducers. The mean flow velocity profiles and the Reynolds stresses within the turbulent boundary layer were obtained using single and crossed hot-wire anemometers, respectively. Adverse and favorable pressure gradients were realized by installing a turnable NACA 0012 airfoil above the plate. The one-point spectrum, the correlation in the streamwise and spanwise directions and the convection velocity for the wall pressure field are analyzed. The effect of the pressure gradients on the wall pressure fluctuations and the corresponding relevant boundary layer parameters are discussed. Based on the measured data and a dataset of four other experiments at three other test facilities, an empirical model of wall pressure spectra for adverse pressure gradient boundary layers is proposed. Goody's model, which is the most used wall pressure spectrum model for zero pressure gradient boundary layers, is served as the basis for the development of the new model. Predictions of the new model and comparisons with other published wall pressure spectral models for adverse pressure gradient boundary layers are made for the selected dataset. The new model shows good prediction accuracy for the selected dataset and a significant improvement compared to the other published models. Furthermore, pressure fluctuations within turbulent boundary layers on a flat plate configuration are simulated using synthetic isotropic and anisotropic turbulence generated by the Fast Random Particle-Mesh Method. The averaged turbulence statistics needed for the stochastic realization is provided by a Reynolds averaged Navier-Stokes simulation. Anisotropy of integral lengths scales and Reynolds stress tensors are implemented for the realization of anisotropic turbulence. To determine the fluctuating pressure, a Poisson's equation is solved with unsteady right-hand side source terms derived from the synthetic turbulence realization. The Poisson's equation is solved via fast Fourier transform using Hockney's method. Due to its efficiency, the applied procedure enables us to study, for high Reynolds number flow, the effect of variations of the modelled turbulence characteristics on the resulting wall pressure spectrum. The contributions to wall pressure fluctuations from the mean-shear turbulence interaction term and the turbulence-turbulence interaction term are studied separately. The results show that both contributions have the same order of magnitude. Simulated one-point spectra and two-point correlations of wall pressure fluctuations are analyzed in detail. Convective features of the fluctuating pressure field are well determined. Good agreement for the characteristics of the wall pressure fluctuations is found between the numerical results and databases from the present measured data and other investigators.