GPPS-TC-2019-0029 NUMERICAL INVESTIGATION OF WALL COOLING EFFECT ON THE TRANSONIC COMPRESSOR PERFORMANCE

In recent years, the effect of heat transfer in the compressors has been investigated. It shows that cooling via compressor surface can improve the overall performance of the axial compressor. In this paper, the mechanism of cooling effect on the transonic flow is studied. Casing cooling is applied in a transonic compressor rotor and a one and a half stage transonic compressor modelling the F class gas turbine first stage, respectively. Effect of cooling is numerically investigated at the near peak efficiency point. By changing the temperature near the casing, both the velocity and speed of sound in front of the rotor near the tip are affected. Cooling affects the shock wave in the flow path, which improves the total pressure rise capability in the tip region. Further, cooling in the inlet guide vane (IGV) is also applied together with casing cooling in the 1.5 stage compressor. It can also improve the aerodynamic performance of compressors. INTRODUCTION Multistage axial compressor is one of the major three components of gas turbines. The aerodynamic performance of compressor affects the efficiency of Brayton cycle. To improve the efficiency of cycle, total pressure ratio of the multistage compressor should be increased without an increase in the number of stages, and the efficiency and operating range of the compressor cannot decreased. Thus, complex flow phenomenon, such as tip leakage flow, shock wave, corner separation, etc., should be controlled. In the compressors, surfaces including blades, hub and casing are usually considered as adiabatic walls. However, the effects of heat transfer between the structure and flow are investigated recently. Surfaces in the compressor are considered as non-adiabatic wall. Since 2011, Ito and Nagasaki (Ito and Nagasaki, 2011; Ito et al., 2012; Ito et al., 2014; Ito et al., 2015) proposed a new intercooled recuperated (ICR) method for aero-engines and studied the effect on the Brayton cycle. They used the stator vanes in the compressor as the air cooler and the vanes in the bypass duct as the radiator in the intercooling system. Five serial cooling channels are applied in the compressor vanes for the convective heat transfer and supercritical carbon dioxide is the coolant. This technique uses already equipped components in engines to increase the efficiency of Brayton cycle, without an increase in space and weight caused by additional heat exchangers. In the precooled turbojet (PCTJ), precooling of the inlet air is widely applied. It can be achieved using a heat sink (such as a cryogenic fuel), or via mass injection (such as water or liquid oxygen). Shah and Tan (Shah and Tan, 2007) studied the overall performance of an axial compressor with heat extraction via blade surfaces. All the surfaces, including blades, hub and casing, are specified as a wall with constant temperature. Numerical results by mean-line method and CFD method indicate that cooling can increase the total pressure ratio and increase the choked mass flow rate with the same rotating speed, which increases the shaft power of compressors. In the re-accelerated transient (also called as “Bodie” transients) of aero-engines, the rotating speed of compressor rapidly changes. Due to the thermal inertia, component temperatures lag behind the main stream temperature. Consequently, there are heat transfer on the surfaces of the components. The main stream temperature rapidly increases in the acceleration of compressor, and it is higher than the temperature of solid wall. The wall of components has a cooling effect on the main stream. First, the unsteady change in temperature leads to the change in geometry of the compressor casing and the tip clearance, which affects the aerodynamic performance. Schulte et al. (Schulte et al., 2008) studied the effect of unsteady heat transfer on the tip clearance of the rotor. Besides, the effect of unsteady heat transfer on the surge margin is evaluated by mean-line method (Kiss and Spakovsky, 2018). It is found that by changing the deviation angle and the load distribution in each