The Influence of Large-Scale, High-Intensity Turbulence on Vane Aerodynamic Losses, Wake Growth, and the Exit Turbulence Parameters

Abstract

An experimental research program was undertaken to examine the influence of large-scale high-intensity turbulence on vane exit losses, wake growth, and exit turbulence characteristics. The experiment was conducted in a four-vane linear cascade at an exit Reynolds number of 800,000 based on chord length and an exit Mach number of 0.27. Exit measurements were made for four inlet turbulence conditions including a low-turbulence case (Tu ≈ 1 percent), a grid-generated turbulence case (Tu ≈ 7.5. percent) and two levels of large-scale turbulence generated with a mock combustor (Tu ≈ 12 and 8 percent). Exit total pressure surveys were taken at two locations to quantify total pressure losses. The suction surface boundary layer was also traversed to determine losses due to boundary layer growth. Losses occurred in the core of the flow for the elevated turbulence cases. The elevated free-stream turbulence was found to have a significant effect on wake growth. Generally, the wakes subjected to elevated free-stream turbulence were broader and had smaller peak velocity deficits. Reynolds stress profiles exhibited asymmetry in peak amplitudes about the wake centerline, which are attributable to differences in the evolution of the boundary layers on the pressure and suction surfaces of the vanes. The overall level of turbulence and dissipation inside the wakes and in the free stream was determined to document the rotor inlet boundary conditions. This is useful information for assessing rotor heat transfer and aerodynamics. Eddy diffusivities and mixing lengths were estimated using X-wire measurements of turbulent shear stress. The free-stream turbulence was found to strongly affect eddy diffusivities, and thus wake mixing. At the last measuring position, the average eddy diffusivity in the wake of the high-turbulence close combustor configuration (Tu ≈ 12) was three times that of the low turbulence wake.

Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

“…Within investigations which generally involve low-speed turbine cascades [3,[59][60][61][62][63], a total pressure loss coefficient Ω = (P oi − P oe )/(P oi − P se ) is employed, which is equivalent to the Y P quantity given by (6). Within this definition, each term is generally determined locally at a particular spatial location.…”

“…Of these investigations, Hoheisel et al [1], Gregory-Smith and Cleak [2], and Ames and Plesniak [3] examine the influences of inlet turbulence on losses across turbine cascades. Hoheisel et al [1] also consider the effects of blade boundary layers, and Ames and Plesniak [3] demonstrate important connections between wake growth and level of freestream turbulence. Moore et al [4] indicate that more than one third of total losses develop downstream of airfoil trailing edges.…”

Heat Transfer Measurements in a Compressible Flow Vane Cascade Showing the Influence of Reynolds Number, Mach Number, and Turbulence Level on Transition and Augmentation of Laminar Heat Transfer by Free-Stream Turbulence

“…Gregory-Smith and Cleak [4] found grid turbulence increased profile losses by 7% but actually improved endwall losses due to the influence of the turbulence on the inlet boundary layer. Additionally, Ames and Plesniak [5] found that their 12% inlet turbulence, produced by a simulated combustor turbulence generator, caused significant "background" losses between the wakes which they attributed to the production of turbulence within the turbine vane passage and the redistribution of endwall losses by the turbulence. More recently, Mihelish and Ames [6] measured aerodynamic losses downstream from the present vane cascade and noted the impact of Reynolds number, turbulence condition, and Mach number on aerodynamic losses.…”

Numerical Predictions of Stanton Numbers, Skin Friction Coefficients, Aerodynamic Losses, and Reynolds Analogy Behavior for a Transsonic Turbine Vane

“…Considerable efforts are also devoted by many researchers in their experimental research programs for calibration and validation of different CFD models. Of the investigations which examine the effects of augmented free-stream turbulence levels, Ames and Plesniak [11] demonstrate important connections between freestream turbulence level and subsonic vane exit losses, wake growth, and wake turbulence characteristics. Radomsky and Thole [12] present measurements of time-averaged velocity components and Reynolds stresses along a turbine stator vane at elevated free-stream turbulence levels.…”