Effects Of Endwall Motion Research Articles

Effects of endwall motion on thermal performance of cavity tips with different squealer width and height

This paper investigates the thermal performance of cavity tips in a transonic high pressure turbine cascade. Numerical methods were first validated and then used to study more cases. The flow physics within the tip gap and the distribution of Nusselt number on the blade tip were presented. The effects of relative motion between the blade tip and the endwall were studied. For both cases with a stationary endwall or a moving endwall, a cavity vortex appears within the tip cavity. It is found that a cavity scraping vortex forms within the tip cavity as the endwall moves relatively to the blade tip, which was not observed before. The effects of the cavity scraping vortex on the distribution of Nusselt number are explained. Then, the effects of the squealer width and height on the thermal performance of the cavity tip were investigated. The flow physics within the tip cavity varies as the squealer geometry changes. As a result, the thermal performance of the cavity tips is different. The results show that increasing the height of the squealer reduces the average Nusselt number on the blade tip. The average Nusselt number and the heat flux on different parts of the blade tip, and the thermal performance of the blade surface near tip region and the loss of different blade tips are also discussed in this paper.

Effects of Endwall Motion on the Aero-Thermal Performance of a Winglet Tip in a HP Turbine

In a gas turbine, the casing endwall moves relative to the blades. In this paper, numerical methods are first validated using experimental results for a stationary endwall. They are then used to study the effects of endwall motion on the aero-thermal performance of both winglet tips with and without tip film cooling at a tip gap of 1.9% C. The endwall motion imposes a tangential force on the flow. A scraping vortex is formed and the flow pattern within the tip gap changes significantly. The tip leakage mass flow rate that exits the tip gap from the suction side edge reduces by about 42% with endwall motion. Overall, the endwall motion reduces the tip leakage loss by 15%. The flow field downstream of the cascade also changes with endwall motion. With endwall motion, the changed flow pattern within the tip gap significantly changes the distribution of the Nusselt number on the winglet tip. For the winglet tip without tip film cooling, the Nusselt number and the heat load decrease with endwall motion. This is mainly due to the reduction in the tip leakage mass flow ratio, which reduces the leakage velocity over the tip. On the winglet tip with tip film cooling, the cooling effectiveness increases by 9% with endwall motion. Combined with the reduced Nusselt number, the heat flux on the winglet tip with tip film cooling reduces by 31% with endwall motion. The cooling effectiveness on the near tip region of the pressure side remains almost unchanged, however, the heat flux rate in this area reduces. This is because the reduced tip leakage mass flow ratio reduces the Nusselt number. With the moving endwall, the thermal performance of the suction side surface of the blade is affected by the scraping vortex. The effects of endwall motion should be considered during the design of the blade tip.

Thermal Performance of Different Cooled Tips in A High-Pressure Turbine Cascade

The thermal performance of the three turbine tips was investigated. The results are presented in terms of heattransfer coefficient (h), cooling effectiveness (η), net heat-flux reduction (NHFR), and heat load. The calculations were performed using a cooled flat tip, a cooled cavity tip, and a cooled suction-side squealer tip in a cascade at a tip gap of 1.6%C. The results were validated using experimental data where possible. For an uncooled flat tip, the fluid dynamics are dominated by flow separation at the pressure-side edge. A significant benefit of ejecting coolant inside this separation bubble is shown. At the coolant mass-flow ratio M c = 0:52%, both the cooled flat tip and the cooled cavity tip are well-protected by the coolant. For the cooled suction-side squealer tip, the coolant lifts off from the tip floor and leads to not only low cooling effectiveness, but also to high heat-transfer coefficients. The effects of the coolant mass-flow ratio on the thermal performance of the tip were presented. The effects of end-wall motion on the thermal performance of the blade tip are found to be small in the current study.

Wake of a Compressor Cascade with Tip Gap, Part 2: Effects of Endwall Motion

The effects of relative motion between the blade tips and endwall on the flow downstream of a linear compressor cascade have been studied. Endwall motion was simulated by using a 0.25-mm-thick Mylar belt propelled ove ra sliding surface beneath the tips of the cascade blades. Three-component mean-velocity and turbulence measurements made in cross sections downstream of the cascade reveal that the wall motion flattens and shears the turbulence and mean-velocity distributions of the vortex. Mean-helicity density plots also show that endwall motion smears the vortex center from a single point (when seen in cross section) into a ribbon that makes an angle of some 30 deg with the endwall. Despite these effects, many critical features of the vortex are almost unaffected by the endwall motion. The vortex produces almost the same magnitude of streamwise mean-velocity deficit, and this deficit still dominates both the mean velocity field and the production of turbulence. Thus, although endwall motion distorts and displaces the leakage vortex it does not fundamentally alter the mechanisms that govern the development of its mean flow and turbulence structure.