Turbine Nozzle Endwall Inlet Film Cooling: The Effect of a Back-Facing Step

Abstract

Film cooling effectiveness was measured on a contoured endwall surface using the pressure sensitive paint (PSP) technique. A double staggered row of holes was adopted to supply cooling air in front of the nozzle leading edges. To simulate realistic engine configuration, a back-facing step was built, which was located upstream from the film injection. Nitrogen gas was used to simulate film cooling flow as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Cooling mass flow was controlled to be from 0.5% to 3.0% of the mainstream mass flow. Film effectiveness distributions were measured on the endwall surface for both smooth (baseline) and back-facing step inlet configurations. For the smooth inlet case, film effectiveness increased nonlinearly with mass flow rate, indicating a strong interference between the cooling jets and the secondary flows. At lower mass flow ratios, the secondary flow dominated the near wall flow field, resulting in a low film effectiveness value. At higher mass flow ratios, the cooling jet momentum dominated the near wall flow field, resulting in a higher film effectiveness. For the back-facing step inlet configuration, the values of film effectiveness were reduced significantly, suggesting a stronger secondary flow interaction. In addition to the comparison between the smooth and back-facing step inlet configurations, comparison to previous data by the authors on a flat endwall was also made.

Heat transfer and film-cooling for the endwall of a first stage turbine vane

“…One of the key findings was that the endwall adiabatic effectiveness distributions showed extreme variations across the vane gap with much of the coolant being swept across the endwall toward the suction side corner. Granser and Schulenberg [18], Colban et al [15], and Zhang and Moon [19] all reported similar adiabatic effectiveness results in that higher values occurred near the suction side of the vane relative to the pressure side. Based on their measurements, Roy et al [20], however, indicated that the coolant migrated toward the pressure side of the vane.…”

Experimental Study on the Improvement of the Film Cooling Effectiveness of Various Modified Configurations Based on a Fan-Shaped Film Cooling Hole on a Flat Plate

“…The pressure-sensitive paint (PSP) method, as proposed by Zhang et al [22,23], was used in this study. PSP is commonly used in experiments to measure the adiabatic film cooling effectiveness, making use of its characteristics and similarity in mass heat transfer.…”

Influence of Combustor Exit Conditions on Cooling Performance of NGV Endwall with Double Row Cooling Holes

“…It was found that the coolant flow dominates the flow field near wall when the coolant MFR is higher than 2%, and the secondary flow is suppressed by the coolant. Zhang and Moon (2003) have studied the influence of the step configuration on the endwall cooling effectiveness. They found that the geometric structure of the upstream step plays an important role in the cooling effectiveness distributions and flow structures near the endwall.…”