Computational fluid dynamics analysis for effect of length to diameter ratio of nozzles on performance of pre-swirl systems

Abstract

In a direct-transfer pre-swirl system, cooling air expands through stationary pre-swirl nozzles and flows through the cavity to the receiver holes located in the rotating turbine disc for blade cooling. This paper investigates the effect of the length-to-diameter ratios of pre-swirl nozzles on the performance of a direct-transfer pre-swirl system in a rotor-stator cavity. The commercial code CFX 12.1 is used to solve the Reynolds-averaged Navier-Stokes equations using the SST turbulence model. Computations are performed for seven length-to-diameter ratios, L/D ¼ 1, 2, 3, 4, 5, 6, and 7, a range of pre-swirl ratios, 0.5 < b p <2.0, and varying turbulent flow parameters, 0.12 < k T < 0.36. The rotational Reynolds number for each case is 10 6 . The computational fluid dynamics model presented in this paper is validated with the experimental results available in the literature. The nozzle exit flow angle decreases as length-to-diameter ratio L/D increases for L/D < 1/tan ( is pre-swirl nozzle angle). When L/D > 1/tan , is approximately invariant and below . The discharge coefficient C d,b for the receiver holes reaches a peak as the fluid in the rotating core is in synchronous rotation with the receiver holes. For small turbulent flow parameters k T , a peak of C d,b can be observed as L/D ¼ 3. For large turbulent flow parameters k T , the shift of the position for a peak occurs. When L/D ¼ 3, the synchronous rotation can be achieved with the smallest value for turbulent flow parameters k T . The adiabatic effectiveness of the system increases with turbulent flow parameters k T . A peak of  b,ad is seen as L/D ¼ 3 for each case. When L/D < 1/tan , there is a significant increase in  b,ad , especially for L/D < 2, with an increase in L/D. When L/D is increased further, a slight decrease occurs. Both performance parameters show that the optimum value for all cases can be achieved as L/D ¼ 3, which is slightly above 1/tan .

Numerical investigation on the flow and heat transfer characteristics in radial pre-swirl system with different fillet radius at the junction of inlet cavity and nozzle

“…Didenko et al [18] performed a numerical study to investigate the effect of geometrical parameters in terms of the cavity width, pre-swirl nozzle location and way of air delivery on the adiabatic effectiveness, loss coefficient, and discharge coefficient. Liao et al [12] and Zhang et al [13,19] numerically studied the influences of geometrical parameters of nozzles on the adiabatic effectiveness and total pressure loss. Variations of radius ratio of pre-swirl nozzles to receiver holes, the preswirl cavity height and the pre-swirl cavity width were selected by Jarzombek et al [20] to investigate its' effects on the adiabatic effectiveness and total pressure loss.…”

Numerical investigation of fluid flow in a rotor–stator cavity with curved rotor disk

“…Using a pre-swirl in rotor-stator cavities reduces the relative total temperature of the air entering the cooling passages in the rotor. Numerous research works have been conducted on pre-swirl flow [25][26][27]. A numerical study by Liao et al [28] has revealed that the pressure ratio has an important effect on the magnitude of heat transfer coefficient and the rotating speed has a significant effect on the displacement of locations with high heat transfer coefficient.…”