Ian Tibbott

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage Flow in a Turbine Cascade

Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip were studied as baseline cases. The flow patterns over the three tips were studied. For the cavity tip and the winglet tip, vortices appear in the cavity and the gutter. These vortices reduce the discharge coefficient of the tip leakage flow. The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of loss. The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increases, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.

The Aerothermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade

The aerothermal performance of a winglet tip with cooling holes on the tip and on the blade surface near the tip is reported in this paper. The investigation was based on a high pressure turbine cascade. Experimental and numerical methods were used. The effects of the coolant mass flow rate are also studied. Because the coolant injection partially blocks the tip leakage flow, more passage flow is turned by the blade. As a result, the coolant injection on the winglet tip reduces the deviation of the flow downstream of the cascade due to the tip leakage flow. However, the tip leakage loss increases slightly with the coolant mass flow ratio. Both the computational fluid dynamics tools and experiments using the Amonia–Diazo technique were used to determine the cooling effectiveness. On the blade pressure side surface, low cooling effectiveness appears around the holes due to the lack of the coolant from the cooling hole or the lift-off of the coolant from the blade surface when the coolant mass flow is high. The cooling effectiveness on the winglet tip is a combined effect of the coolant ejected from all the holes. On the top of the winglet tip, the average cooling effectiveness increases and the heat load decreases with increasing coolant mass flow. Due to its large area, the cooled winglet tip has a higher heat load than an uncooled flat tip at engine representative coolant mass flow ratio. Nevertheless, the heat flux rate per unit area of the winglet is much lower than that of an uncooled flat tip. The cycle analysis is carried out and the effects of relative tip-to-casing endwall motion are address.

Velocity and Turbulence Intensity Profiles Downstream of a Long Reach Endwall Double Row of Film Cooling Holes in a Gas Turbine Combustor Representative Environment

The continuous demand from the airlines for reduced jet engine fuel consumption results in increasingly challenging high pressure turbine nozzle guide vane (NGV) working conditions. The capability to reproduce realistic boundary conditions in a rig at the combustor-turbine interaction plane is a key feature when testing NGVs in an engine-representative environment. A large scale linear cascade rig to investigate NGV leading edge cooling systems has been designed with particular attention being paid to creating engine representative conditions at the inlet to the NGVs. The combustor simulator replicates the main features of a rich-burn design including large dilution jets and extensive endwall film cooling. A three-dimensional computational domain including the entire combustor simulator has been created and RANS CFD simulations have been run in order to match Reynolds number and mainstream-to-coolant momentum flux ratio; velocity and turbulence measurements have been acquired at the NGV inlet plane at ambient temperature. In this engine-representative environment the authors focused their attention on the flow field downstream of different endwall film cooling holes configurations: three arrangements of a double row of staggered cylindrical holes (lateral pitch-to-diameter ratio of 2–3–6) and one with intersecting holes (intersecting angle of 90°) are experimentally and numerically analyzed. Velocity, turbulence intensity and integral length scales are predicted and measured for a density ratio of 1 and coolant-to-mainstream momentum flux of 6. A hot wire sensor was mounted on a two-axis traverse mechanism able to move the probe in the spanwise and lateral directions. Three slots allowed to reposition the traverse and take measurements at three downstream locations (stream-wise distance-to-diameter ratio of 4.2–9.2–14.2). The research confirmed the strong influence of the endwall coolant on the flow field at the NGV inlet plane and the hole spacing results a key parameter in managing the film development. Closer-spaced hole configurations can assure an effective film coverage. The integral length scales are strongly connected to the hole diameter and spacing. Intersecting holes can potentially reduce the amount of required coolant at a fixed pressure ratio, but they offer worst film performance than cylindrical holes. RANS simulations proved to be able to get the main trends shown by the measurements.Copyright

The Aero-Thermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade

The aero-thermal performance of a winglet tip with cooling holes on the tip and on the blade surface near the tip is reported in this paper. The investigation was based on a high pressure turbine cascade. Experimental and numerical methods were used. The effects of the coolant mass flow rate are also studied. Because the coolant injection partially blocks the tip leakage flow, more passage flow is turned by the blade. As a result, the coolant injection on the winglet tip reduces the deviation of the flow downstream of the cascade due to the tip leakage flow. However, the tip leakage loss increases slightly with the coolant mass flow ratio. Both the CFD tools and experiments using the Amonia-Diazo technique were used to determine the cooling effectiveness. On the blade pressure side surface, low cooling effectiveness appears around the holes due to the lack of the coolant from the cooling hole or the lift-off of the coolant from the blade surface when the coolant mass flow is high. The cooling effectiveness on the winglet tip is a combined effect of the coolant ejected from all the holes. On the top of the winglet tip, the average cooling effectiveness increases and the heat load decreases with increasing coolant mass flow. Due to its large area, the cooled winglet tip has a higher heat load than an uncooled flat tip at engine representative coolant mass flow ratio. Nevertheless, the heat flux rate per unit area of the winglet is much lower than that of an uncooled flat tip.Copyright

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, but 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.© 2011 ASME