Non-Dimensional Parameter for Characterization of Wall Shear Stress from Underexpanded Axisymmetric Impinging Jets

[+] Author and Article Information
Patrick Fillingham

Department of Mechanical Engineering, University of Washington, Seattle, WA, 98105

Harikrishnan Murali

Department of Aeronautics and Astronautics University of Washington, Seattle, WA, 98105

Igor Novosselov

Department of Mechanical Engineering, University of Washington, Seattle, WA, 98105

1Corresponding author.

ASME doi:10.1115/1.4037035 History: Received September 16, 2016; Revised April 20, 2017


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 axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle while varying the height to diameter ratio (H/D) and the inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. A Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP<1), (ii) transitional (1<DJP<2), and (iii) supersonic impingement (DJP>2). It is observed that wall shear stress is limited to a finite value due to jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime. Additionally, the formation of shock structures in the wall flow were observed for DJP>2, resulting in difficulties with dimensionless analysis. In subsonic impingement and transitional regimes, equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships, wall shear stress can be predicted at all locations along the impingement surface.

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