Studies on Aero-Thermal Performances of Leakage Flows Injection from the Endwall Slot in Linear Cascade of High-Pressure Turbine

Abstract

Present studies focus on thermal and aerodynamics investigations of leakage flow injection through a slot which is located at upstream of blade leading edge. In the real gas turbine, this slot is actually the gap between the combustor and turbine endwall as for the maintenance works consideration. However, the slot induced to the leakage phenomenon caused by the bypassed air that coming from the compressor side for turbine cooling purposes. Gas turbine manufactures intended to minimize these kinds of leakages in maintaining the aerodynamics performance of the turbine cascade. However, previous researchers found that the leakages could be used to protect the endwall surfaces from the hot gas since it could not be completely prevented. Thus, present study investigated the potential of leakage flows as a function of film cooling. Chapter 1 gives some introduction on present works about the need of film cooling to protect the wall surfaces. Several related studies by previous researchers are also explained. Chapter 2 explained the details of methodologies used in present studies. A leakage flow with 90 deg of injection angle was considered as for the baseline configuration. Liquid crystal was used for the time-varying endwall temperature measurement. The transient method was applied to determine the film cooling effectiveness, eta and the heat transfer coefficient, h for the thermal performance evaluations. The details of the aerodynamics performances was revealed by conducting 5-holes Pitot tube measurement at blade downstream plane (1.25C(ax)) and the total pressure loss coefficient, C(pt) as well as the flow vorticity, zeta contours were plotted. Furthermore, the effects of the leakage flow with the mainstream consist of complex secondary flows structures also have been revealed by numerical investigation. In present study, the flow is analyzed by using the three-dimensional,steady Reynolds-averaged Navier-Stokes (RANS) equations by conducting Shear Stress Transport, SST turbulence model. The leakage was injected with a various amount (which is described by mass flow ratio, MFR) to observe the eta performance at different injection cases. Chapter 3 provided details discussions on the aero and thermal performances of the leakage injection. Both experimental and numerical presented the performance of eta increased when the injection amount increases. SST turbulence model captured the presence of the separation flow that caused the lower h region which also captured by the experimental. As for the aerodynamics performance, C(pt) was increased after the introduction of leakage injection and indicated the increase trend when the MFR was being increased. Leakage flows were prevented to be injected into high pressure region thus they tended to move towards lower pressure region which is between two stagnation regions. As a result, a newly generated vortex core was predicted. This accumulated vortex core (AFV) is considered to contribute to the additional losses at blade downstream. Chapter 4 presents the numerical investigation on the modification of slot configurations such as positions and orientations. The leakages flow by shallower injection angle, beta towards mainstream was predicted to reduce the strength of the passage vortex thus increase the aerodynamics performance particularly at higher injection cases. Additionally, eta also obviously increased by the slot orientation. To move away the slot from the blade LE was predicted to increase both aero and thermal performance. The leakage flow could laterally be penetrated to the mainstream and stayed closer on endwall surfaces. This is due to the fewer blockages influenced by the stagnation region since the slot located far away from the blade LE. In contrast, move the slot closer towards blade LE just increased the C(pt). Furthermore, locate the slot closer to blade LE could not increase the protection layer except the level of eta. Finally, Chapter 5 highlights the important points to be concluded based on present investigations. The potential of the leakage flows to protect the endwail surfaces has been proven and they were highly influenced by the secondary flows behavior on the endwall region. However, to increase the performance of cooling by increasing the injection amounts unfortunately reduces the aerodynamics performance due to the increase strength of the secondary flow vortices. The leakage flow with a shallow injection angle towards mainstream are predicted to provide a positive trends of cooling performance with a lower aerodynamic losses especially at higher leakage flow injection cases.