Numerical investigation of the heat transfer due to coaxial swirling turbulent jet impingement on heated flat surfaces

Abstract

Numerical investigation of the fluid flow and heat transfer process due to a turbulent coaxial swirling jet, impinging on an isothermally heated flat surface is conducted using the ANSYS Fluent commercial code. The computational data is validated against published experimental and numerical data on the same geometrical configuration for non-swirling coaxial jets. The performance of a few turbulence models is evaluated, and the SST k-ω turbulence model is chosen over the other models based onthe overall good agreement with thepublished data. The coaxial jet is constructed by inserting a thin circular tube inside a coaxial pipe. The two fluid streams, inside the inner tube and within the annular space between the inner tube and outer pipe, flow with different average velocities. The flow and geometric parameters are the average velocity ratio of the outer and inner jets, the diameter ratio of the inner and outer pipes, jet exit Reynolds number, the swirl strength, and the non-dimensional jet exit to target plate separation distance. Computations are performed for various combinations of these parameters to investigate the effects of the parameters, especially the swirl strength, on the coaxial jet impingement heat transfer. Results are presented in terms of the streamlines, isotherms, and swirl velocity contours in the flow domain; pressure coefficient and local and Nusselt number distribution on the heated surface; and average Nusselt numberat the heated surface; at various combinations of the parameters. The coaxial jet causes higher and more uniform heat transfer over the impingement surface compared to that for a single jet. The swirl affects the mixing and jet spreading, which in turn modifies the heat transfer process resulting in diminished or enhanced heat transfer compared to a non-swirling jet.