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

Abstract

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.

Prediction and augmentation of nozzle guide vane film cooling hole pressure margin

“…The plenum coolant temperatures are recorded by thermocouples, due to the coolant temperature rise and density reduction through the blower. The core into the simulator is inferred using an upstream pitot tube, which was referenced to the detailed NGV mainstream inlet velocity distribution measured by Cresci et al (2015a). The NGV throat Reynolds number based upon the chord varies between approximately for no NGV coolant flow and 7.2 for the maximum investigated NGV coolant .…”

“…As the main body of the central NGV is uncooled, it lacks several downstream pressure side (PS) cooling hole rows and a trailing edge slot, which would be present in an engine. Cresci et al (2015aCresci et al ( , 2015bCresci et al ( , 2015c provide more details about the rig and the flow properties approaching the NGV cascade. The two pressure-tapped leading edges used were 3D printed.…”

Film Cooling Effectiveness Downstream of Trailing Edge Slots Including Cutback Surface Protuberances

“…An example of a pressure surface slot cooling design is shown in Figure 1. Aside from blades and vanes, slot cooling also has applications in other components that require film cooling and use rows of film cooling holes, such as those studied by Cresci et al [3].…”

The Effects of Combustor Cooling Features on Nozzle Guide Vane Film Cooling Experiments

“…For the outer endwall cooling (the inner endwall cooling is not used in this study), the ratio J E is calculated using the combined breakout area of the holes to determine v c . The combustor-turbine interface plane temperature, turbulence, and velocity profiles at fixed J D = 9 and J E = 6 were experimentally measured by Cresci et al [15]- [17]. Turbulence intensities were approximately 18% near the midspan and 25% just downstream of the outer endwall film injection.…”