Investigation of Unsteady Heat Transfer from an Axisymmetric Impinging Synthetic Jet on a Constant Heat Flux Disk

An investigation of unsteady flow and heat transfer from an axisymmetric impinging synthetic jet positioned on a constant heat flux disc is presented. A synthetic jet is a zero net mass flux jet that provides an unsteady flow without any external source of fluid. The continuity, the momentum and the energy equations are solved in an axisymmetric domain. Due to synthetic jet oscillations, the inlet velocity is given as a sinusoidal function. To eliminate the effect of initial conditions on the results, instantaneous Nusselt number is monitored at some points over the time, and analysis has been continued over 150 cycles to ensure the periodicity of results. A complementary grid and time step independence study is carried out. To show that the results are independent of grid size, the problem is solved with three different grid sizes. Also, to ensure that the time-step size does not effect the results, the problem is solved in four different time-step sizes to find the optimum value of time step size. Three two-equation turbulence models are applied to the problem, namely, the standard k-E, low-/Re k-E and SST/k-? models. The present Result are validated against the available experimental data and they show that SST/k-? (فرمول در نسخه اصلی)turbulence model is more accurate and reliable than the other two models for predicting heat transfer from an impinging synthetic jet. A comparative study is conducted to find out the effect of frequency on the heat transfer rate. Results indicate that as the frequency increases the heat transfer is enhanced. Also, results that are compared with the data of steady jet show that in the case with the highest value of frequency, the time-averaged Nusselt number is even greater than the case of steady jet with the velocity equal to the maximum velocity of synthetic jet.

کلیدواژه ها:

Synthetic jet ، unsteady flow ، heat transfer ، turbulence modeling ، impinging jet