Coherence of wall pressure fluctuations in zero and adverse pressure gradients

The wall pressure fluctuations induced by turbulent boundary layers on a flat plate model were measured with an L-shaped array of Kulite miniature pressure sensors. By installing a NACA airfoil above the plate with an adjustable angle of attack, different adverse pressure gradients were produced on the plate. The streamwise and spanwise coherence and coherence lengths of the wall pressure fluctuations are calculated for zero and adverse pressure gradient flows. The effect of the pressure gradient on the coherence and coherence lengths in both streamwise and spanwise directions is quantified. Based on the results of the present test cases and selected published datasets in zero pressure gradients, covering the range of Reynolds numbers based on the momentum thickness between 3300 and 42000, the Reynolds number dependence of the streamwise wall pressure coherence is discussed and mathematically expressed. A coherence length model for zero pressure gradient boundary layers, taking into account the Reynolds number effect, is proposed based on scaled spectra of the coherence lengths. In comparison with the other published models, the present model achieves a considerable improvement of the prediction accuracy for boundary layer flows, covering a large range of Reynolds numbers. Furthermore, an evaluation of the Corcos model and the Smol'yakov and Tkachenko model for prediction of the off-axis coherence of the fluctuating wall pressure field is made.

Automated summary

The study investigates the effects of adverse pressure gradients induced by different angles of attack of a NACA airfoil on wall pressure fluctuations on a flat plate model. The analysis includes calculations and quantification of streamwise and spanwise coherence and coherence lengths, proposes a coherence length model based on Reynolds number effects, and achieves considerable improvement in prediction accuracy compared to other models. Additionally, evaluations are made on the prediction accuracy of off-axis coherence of fluctuating wall pressure field using the Corcos model and the Smol'yakov and Tkachenko model.