Three dimensional design methods have been usually adopted to turbine blades in order to control the spanwise variation of flow fields or to reduce secondary flows. Most of previous studies have reported the effect 148 of three dimensional design method on subsonic or transonic compressors and fans. A small number of studies have been presented for the aerodynamic sweep effect on the supersonic flows with high pressure ratio.
This dissertation aims to investigate the effect of the rotor blade sweep and nozzle-rotor axial gap on the performance characteristics of a small supersonic axial flow impulse turbine used in turbopumps of liquid propellant rocket engines(LPRE).
For these objectives, first, the flow characteristics of the supersonic impulse turbine selected as a reference model were examined in detail, and next, the turbine performance with varying nozzle-rotor axial gap was analyzed for four different axial gap conditions corresponding to 6%, 10%, 20% and 30% of the rotor blade height. Last, the forward sweep(-15°, FSW) and the backward sweep(+15°, BSW) models of first stage rotor blade sweep which was one of the three dimensional design method were considered and the results were compared with the reference model(0°, NSW). Different tip gap conditions, “no tip gap” (NTG) and “with tip gap”(WTG), were given to the swept blade cases in order to examine the effect of blade sweep on tip gap leakage flows.
The analysis for the 1/25 annulus zone of model turbine with rotational periodic condition was carried out using the three-dimensional unsteady viscous compressible flow equations with a SST 2-equation turbulence model. The flow equations are solved by using a second order upwind scheme and second order accurate implicit time integration
scheme. As a result of nozzle-rotor axial gap calculations, the turbine efficiency showed good agreement with previous studies, and it was found that there was certain regions in which the turbine efficiency decreased drastically, followed by a region of no significant change. It is examined that the turbine performance characteristics could change depending on the influence of leading edge shock to the nozzle outlet, and turbine loss increased in the hub area and decreased in the area over the mid
span while the axial gap increased.
As a result of the sweep blade simulation, the backward sweep model (+15°, BSW) showed better performance in incidence angle, Mach number distribution, and entropy rise compared with no sweep model.
The sweep angle had a considerable effect on the mass flow rate of leakage flow through tip gap in WTG case calculation. The mass flow rate of tip leakage flow in BSW model showed about 71% of that in the no sweep model (0°, NSW) and that in the forward sweep model (-15°,
FSW) showed about 121% value of NSW model.
With the blade static pressure distribution result, the backward sweep model (+15°, BSW) showed that hub and tip loading was increased and midspan loading was reduced compared with no sweep model while the
forward sweep model (-15°, FSW) showed the opposite result. The positive sweep model also showed a good aerodynamic performance around the hub region compared with other models. Overall, the positive sweep angle enhanced the turbine efficiency.