Full-coverage film cooling. Part 1. Three-dimensional measurements of turbulence structure

Abstract

Hydrodynamic measurements were made with a triaxial hot wire in the full-coverage region and the recovery region following an array of injection holes inclined downstream, at 30° to the surface. The data were taken under isothermal conditions at ambient temperature and pressure for two blowing ratios: M = 0·9 and M = 0·4. (The ratio M = ρjetUjet/ρ∞U∞, where U is the mean velocity and ρ is the density. Subscripts jet and ∞ stand for injectant and free stream, respectively.) Profiles of the three mean-velocity components and the six Reynolds stresses were obtained at several spanwise positions at each of five locations down the test plate.In the full-coverage region, high levels of turbulence kinetic energy (TKE) were found for low blowing and low TKE levels for high blowing. This observation is especially significant when coupled with the fact that the heat transfer coefficient is high for high blowing, and low for low blowing. This apparent paradox can be resolved by the hypothesis that entrainment of the mainstream fluid must be more important than turbulent mixing in determining the heat transfer behaviour at high blowing ratios (close to unity).In the recovery region, the flow can be described in terms of a two-layer model: an outer boundary layer and a two-dimensional inner boundary layer. The inner layer governs the heat transfer.

Effects of Flow Oscillations in the Mainstream on Film Cooling

“…This is somewhat expected because the Fourier analysis showed that the range of the most dominant frequencies of the combustor unsteady pressure data was in As mentioned earlier, at a high blowing ratio of M = 1.0, the coolant jet lift-off is generated under steady flow conditions (0 Hz), resulting in the entrainment of hot mainstream gases underneath the jet. The entrainment does not lead to much mixing near the wall [46]. If the oscillation frequency is increased from 0 to 90 Hz, more entrainment is induced under the cooling jet resulting in less disturbance and a lower increase of the heat transfer coefficient or the Stanton number ratio.…”

Heat transfer model with two heat transfer coefficients along a multiperforated plate — Application to combustion chamber wall cooling

“…The cold case presents the advantage to lead to a well known two temperatures problem. Indeed the injection temperature equals to the mainflow temperature, there is no more difficulty to calculate a heat transfer coefficient using the expression (1): ~0cv = ~0 d i s s i -~0arr--(Pray = he" (Tw -Te) (1) where Tw is the wall temperature measured by infrared thermography (Fig.3). We calculate its value along three ylD axes (y/D = -1.5, 0, and +1.5) (Fig.2).…”

Full-Coverage Film Cooling: A One-Equation Model of Turbulence for the Calculation of the Full-Coverage and the Recovery-Region Hydrodynamics

“…when equation (2) is substituted in (3) along with effective free stream velocity the following equation is obtained: (4) χ' is the distance from the virtual origin of the internal boundary layer. It was argued earlier that an internal boundary layer starts growing whenever there is a sudden change in the surface conditions.…”