CALCULATION OF DISK TEMPERATURES IN GAS TURBINE ROTOR-STATOR CAVITIES USING CONJUGATE HEAT TRANSFER

The present study deals with the numerical modeling of the turbulent flow in a rotor-stator cavity with or without imposed through flow with heat transfer. The commercial finite volume based solver, ANSYS/FLUENT is used to numerically simulate the problem. A conjugate heat transfer approach is used. The study specifically deals with the calculation of the heat transfer coefficients and the temperatures at the disk surfaces. Results are compared with data where available. Conventional approaches which use boundary conditions such as constant wall temperature or constant heat flux in order to calculate the heat transfer coefficients which later are used to calculate disk temperatures can introduce significant errors in the results. The conjugate heat transfer approach can resolve this to a good extent. It includes the effect of variable surface temperature on heat transfer coefficients. Further it is easier to specify more realistic boundary conditions in a conjugate approach since solid and the flow heat transfer problems arc solved simultaneously. However this approach incurs a higher computational cost. In this study, the configuration chosen is a simple rotor and stator system with a stationary and heated stator and a rotor. The aspect ratio is kept small (around 0.1). The flow and heat transfer characteristics are obtained for a rotational Reynolds number of around 10(6). The simulation is performed using the Reynolds Stress Model (RSM). The computational model is first validated against experimental data available in the literature. Studies have been carried out to calculate the disk temperatures using conventional non-conjugate and full conjugate approaches. It has been found that the difference between the disk temperatures for conjugate and non-conjugate computations is 5 K for the low temperature and 30 K for the high temperature boundary conditions. These represent differences of 1% and 2% from the respective stator surface temperatures. Even at low temperatures, the Nusselt numbers at the disk surface show a difference of 5% between the conjugate and non-conjugate computations, and far higher at higher temperatures.