NUMERICAL INVESTIGATION OF THE EFFECT OF AN AXIAL PRE-SWIRL NOZZLE WITH A RADIAL ANGLE IN A PRE-SWIRL ROTOR-STATOR SYSTEM

Pre-swirl nozzles are often used in gas turbines to deliver the cooling air to the turbine blades. The static axial nozzles swirl the cooling air in the direction of rotation of the turbine disk, thereby reducing the relative total temperature of the air. Most studies about nozzles focus on its shape, radial location, tangential angle to reduce the pressure loss and increase the temperature drop of the pre-swirl system, but few of them consider the benefit of a radial angle of nozzles. This paper investigated numerically the performance of a pre-swirl system whose pre-swirl nozzles have a radial angle. Six radial angles are selected to study the flow dynamics of a direct-transfer pre-swirl system in terms of the total pressure loss coefficient of the pre-swirl cavity, the discharge coefficient of the receiver holes, and the adiabatic effectiveness. It is shown that the nozzles with radial angles can adjust the tangential velocity and radial velocity and thus can influence the performance of a pre-swirl system. There is a lowerest value of total pressure loss in pre-swirl cavity, that is alpha=90 degrees, which can hardly be influenced by the radial angle of nozzle and pressure ratio pi. For a specific swirl ratio beta(infinity) there exists an optimal alpha(opt) where the discharge coefficient of receiver hole is maximum. Moreover, alpha(opt) decreases as pressure ratio pi increases. And so is the adiabatic effectiveness Theta(ad).