Effect of micro rib on aerothermal dynamic in channel flow

Abstract

In the present development of gas turbine, there is a main contradiction between the limited amount of cold air, the pressure head in the gas supply system and the large flow loss caused by the cooling unit inside the turbine blade. It leads to demands for the cooling techniques to provide efficient heat transfer with lower pressure loss. Surface micro turbulator is considered as a potential cooling technique. In this study, numerical simulation and experimental research were undertaken to evaluate the turbulent flow heat transfer and pressure loss in channel with a typical 2-D micro rib on one wall with different rib heights. Investigated rib heights range from 0.0013~0.053 of the channel hydraulic diameter ratio(h/D). The Reynolds number is kept at 20,000 to control the inlet boundary layer thickness, which makes the height of all cases located between the viscous layer and the log-law region in the boundary layer with a dimensionless height h+=2~80. Reynolds-Averaged Navier–Stokes(RANS) and Large Eddy Simulation(LES) results were validated by experiment. The results show that the pressure loss and heat transfer show different trends with the h+, which is mainly due to the enhancement of near-wall turbulence caused by the small rib height and the form drag caused by the large rib height. Furthermore, the analysis of near-wall turbulence characteristics given by LES indicates the enhancement of the normal turbulence fluctuation by the small rib within the turbulent boundary layer transition zone dominates the heat transfer enhancement downstream of the rib. the heat transfer is enhanced and the pressure loss is small when the rib height changes in the boundary layer, Which leads to a better overall thermal performance(OTP). The conclusion affirms that micro rib is a potential cooling technique to attain high heat transfer performance with low pressure loss. which is of great significance to enhance the overall efficiency of gas turbine.