The Effect of Incident Wake Conditions on the Mean Heat Transfer of an Airfoil

Abstract

The flow phenomena of wakes shed by upstream blade rows is a well-known problem in turbomachinery, which influences blade forces, vibrations, losses, and heat transfer. With respect to the heat load to turbine blades, this problem becomes even more complex because of the interaction between wake, potential flow, and the boundary layer along the surface of the airfoil. Experimentally evaluated mean heat transfer coefficients obtained under different unsteady initial conditions are reported. The heat transfer measurements have been carried out in the cascade test facility at the ITS in Karlsruhe, using a rotating bar wake generator placed upstream of the cascade to simulate the wake passing process. The variation of the wake parameters includes different wake passing frequencies, cascade inlet Reynolds numbers, and wake inclination angles. In addition, the relevant parameters of the unsteady wake have been measured by means of a fixed hot-wire anemometer using the ensemble-average technique. The results are compared to those from the literature for the wake of a cylinder in crossflow. They also serve as experimental base for parallel theoretical analyses.

Unsteady Wake Over a Linear Turbine Blade Cascade With Air and CO2 Film Injection: Part I — Effect on Heat Transfer Coefficients

“…Many investigations have been made to study the effect of unsteady wake and mainstream turbulence on the flow field and heat transfer coefficients of a downstream turbine blade. , , Blair et al (1989aBlair et al ( , 1989b, Blair (1992), Camci and Arts (1990), Dunn (1986), Dunn et al (1986Dunn et al ( , 1989Dunn et al ( , 1992, and Nirmalan and Hylton (1990) conducted experiments in actual gas turbine engines; whereas, Doorly (1988), Dullenkopf et al (1991), Dullenkopf and Mayle (1992), Rodi (1989, 1992), O'Brien and Capp (1989), Priddy and Bayley (1988), Wittig et al (1987Wittig et al ( , 1988, and Han et al (1993) did laboratory simulations of upstream unsteady wake conditions. Two techniques to produce unsteady wake have been used in laboratory simulations.…”

“…Two techniques to produce unsteady wake have been used in laboratory simulations. Rodi (1989, 1992), and Priddy and Bayley (1988) used a squirrel cage type wake generator; whereas, Doorly (1988), Dullenkopf et al (1991), Dullenkopf and Mayle (1992), O'Brien and Capp (1989), Wittig et al (1987Wittig et al ( , 1988, and Han et al (1993) used a spoked wheel type wake generator. Mayle and Dullenkopf (1990) and Mayle (1991) recently developed a theory to incorporate unsteady effect into a steady flow analysis by introducing a time-averaged intermittency factor.…”

Direct numerical simulation of heat transfer from the stagnation region of a heated cylinder affected by an impinging wake

“…it was approximately homogeneous and isotropic. Dullenkopf, Schulz & Wittig (1991) and Liu & Rodi (1994a, b) performed heat transfer measurements of flow over turbine blades with incoming wakes, i.e. where the free-stream turbulence was concentrated in periodically passing wakes.…”

Periodic Unsteady Flow Aerodynamics and Heat Transfer: Studies on a Curved Surface, Combined Part I and II

“…Besides the aforementioned results, it was found that an increase in wake passing frequency results in a shift of the transition region toward the leading edge due to increased turbulence activities. Dunn (1986), Dring et al (1986), Wittig et al (1988), Dullenkopf et al (1991), Liu and Rodi (1992), and Han et al (1993) Dunn (1986) and Doorly et al (1985) determined the heat transfer coefficient by using quick response sensors to detect the real time variation on the blade surface heat transfer induced by unsteady wakes. However, Liu and Figure shows a schematic picture of the wake flow within a multistage turbine in an absolute and relative frame of reference.…”