Characterization of Wall Shear Stress of Underexpanded Impinging Jets

Abstract

Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field resulting from normally impinging jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled, considering a large reservoir, while varying the diameter (D), height to diameter ratio (H/D) and the nozzle exit pressure ratio (NPR). Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. A Jet Parameter, derived through H, D and NPR, is developed to characterize shear stress for subsonic impingement. It is observed that the rate of increase of the wall shear stress reduces with the presence of supersonic flow at the wall. In subsonic impingement regime, equations as a function of the Jet Parameter are obtained for the maximum wall shear stress magnitude and maximum shear stress location. Using these relationships, the peak wall shear stress and its location along the impingement surface can be predicted at different jet configurations.