Influence of Surface Roughness on the Aerodynamic Losses of a Turbine Vane

Abstract

The effects of surface roughness on the aerodynamic performance of a turbine vane are investigated for three Mach number distributions, one of which results in transonic flow. Four turbine vanes, each with the same shape and exterior dimensions, are employed with different rough surfaces. The nonuniform, irregular, three-dimensional roughness on the tested vanes is employed to match the roughness which exists on operating turbine vanes subject to extended operating times with significant particulate deposition on the surfaces. Wake profiles are measured for two different positions downstream the vane trailing edge. The contributions of varying surface roughness to aerodynamic losses, Mach number profiles, normalized kinetic energy profiles, Integrated Aerodynamics Losses (IAL), area-averaged loss coefficients, and mass-averaged loss coefficients are quantified. Total pressure losses, Mach number deficits, and deficits of kinetic energy all increase at each profile location within the wake as the size of equivalent sandgrain roughness increases, provided the roughness on the surfaces is uniform. Corresponding Integrated Aerodynamic Loss IAL magnitudes increase either as Mach numbers along the airfoil are higher, or as the size of surface roughness increases. Data are also provided which illustrate the larger loss magnitudes which are present with flow turning and cambered airfoils, than with symmetric airfoils. Also described are wake broadening, profile asymmetry, and effects of increased turbulent diffusion, variable surface roughness, and streamwise development.

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

“…The data of Zhang and Ligrani [8] show that magnitudes of Integrated Aerodynamic Losses change by much larger amounts as either the freestream Mach number or turbulence intensity are altered, when the airfoil is roughened (compared to smooth airfoil results). Other recent investigations are described by Zhang et al [37,38] and by Zhang and Ligrani [39,40].…”

“…With this approach, the local stagnation pressure loss is normalized by a quantity which does not vary with cascade exit location. Zhang et al [5,37,38], Jackson et al [54], Chappell et al [55], and Zhang and Ligrani [8,27,39,40] employ integrated aerodynamic loss IAL to quantify aerodynamic losses in turbine components. Dimensional magnitudes of Integrated Aerodynamic Loss, IAL, are determined by integrating profiles of (P oi − P oe ) with respect to y in the transverse flow direction across the wake for one single vane spacing, from −p/2 to p/2 [54].…”

“…section. Additional details on experimental apparatus and procedure details are provided by Zhang et al [37,38], and Zhang and Ligrani [27,39,40]. Wake profile data are presented for two different locations downstream the vane trailing edge, which illustrate the influences of varying freestream turbulence intensity level, surface roughness, and vane Mach number on local aerodynamic losses, Integrated…”

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

“…For example, Roberts and Yaras [15] present experimental results documenting the combined effects of surface roughness and mainstream turbulence level on boundary-layer transition. Zhang et al [16] investigate the influences of surface roughness effect on aerodynamic losses produced by a cambered turbine vane. A technique to determine the skin friction coefficients from wake data measured downstream of symmetric turbine airfoils with rough surfaces is described by Zhang et al [17].…”

Effects of surface roughness on deviation angle and performance losses in wet steam turbines

“…Performance tests were conducted in a low-speed, single-stage, axial flow turbine with roughened blades. Afterwards, Zhang et al [5] studied the influence of surface roughness on the aerodynamic losses of a turbine vane. They employed the nonuniform, irregular and three-dimensional roughness on the tested vanes.…”