(126d) Large Eddy Simulation of a Synthetic Jet Using Multi-Relaxation Time Lattice Boltzmann Method

Synthetic jet is an effective methodology for heat removal and has advantages over impinging jet in several aspects. It has simple structure and its size can be reduced easily to be put into small sized electronic devices for the purpose of cooling. Turbulent mixing of synthetic jet is a main mechanism for cooling and further flow separation in adverse-pressure-gradient boundary layer is delayed [1]. Flow characteristics in synthetic jet are not easy to analyze because complex turbulent flow is generated near an orifice. Conventional computational fluid dynamics with various turbulent models including two equations and large eddy simulation (LES) have been applied to describe the complex flow physics [2, 3]. For enhanced designs which can expedite heat transfer, intensive study on the operating parameters such as depth of cavity, size and shape of orifice, and stroking amplitude and frequency of the diaphragm needs to be performed [4, 5, 6]. In this work, we utilize lattice Boltzmann method (LBM) to figure out the design criteria of synthetic jet which is specifically useful in handling transient phenomena including complex system like turbulence [7]. A LES model is implemented and multi-relaxation time technique is applied to simulate the synthetic jet in an accurate and stable manner. This novel approach enables us to estimate the optimal jet core velocity and turbulent mixing intensity via parametric study of orifice size, the operating frequency, and cavity parameters. Our LBM analysis provides flow characteristics to enhance the heat transfer which is quantified using convective turbulent heat transfer equation.

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