CFD Conjugate Analysis of a Jet-Impingement Configuration With Sudden Changes in Heating and Cooling Loads

Abstract

The temperature in a material could exceed the maximum allowable during transients when the heat load is suddenly increased despite a corresponding increase in cooling. This is because there is a time lag in the response of the material. Unsteady RANS based on the shear-stress transport model with conjugate analysis were used to study the unsteady heating and cooling of a superalloy flat plate with a thickness of 1 mm. The flat plate was initially at steady-state conditions, heated on one side by a constant heat flux of 10 W/cm2 and cooled on the other side by impingement of air jets such that the maximum temperature in the plate was just below 900 °C, where 900 °C was taken to be the maximum allowable material temperature. Suddenly, the heating load was increased from 10 W/cm2 to 68 W/cm2 with a corresponding increase in the cooling such that the maximum temperature in the plate remains just below 900 °C when steady state is reached. Results obtained show that though the maximum temperatures at the two steady states are just below 900 °C, the highest temperature in the material can exceed 900 °C by up to 14 seconds during the transient from one steady state to the other. Thus, the minimum cooling flow based on steady-state conditions are inadequate during the transient process if the sudden heating and cooling occurred simultaneously. However, if the increase in cooling preceded the sudden increase in heating by a sufficient amount of time (i.e., pre-cooling), then over temperature was found to not occur during the transient. This paper presents results that show the unsteady flow and heat transfer in the fluid phase and the transients in the solid phase with and without pre-cooling.