The present study experimentally investigates a turbulent jet in crossflow relevant to film cooling applications. The jet is inclined at 30°, and its mean velocity is the same as the crossflow. Magnetic resonance imaging is used to obtain the full three-dimensional velocity and concentration fields, whereas Reynolds stresses are obtained along selected planes by Particle Image Velocimetry. The critical role of the counter-rotating vortex pair in the mixing process is apparent from both velocity and concentration fields. The jet entrainment is not significantly higher than in an axisymmetric jet without crossflow, because the proximity of the wall inhibits the turbulent transport. Reynolds shear stresses correlate with velocity and concentration gradients, consistent with the fundamental assumptions of simple turbulence models. However the eddy viscosity is strongly anisotropic and non-homogeneous, being especially low along the leeward side of the jet close to injection. Turbulent diffusion acts to decouple mean velocity and concentration fields, as demonstrated by the drop in concentration flux within the streamtube issued from the hole. Volume-averaged turbulent diffusivity is calculated using a mass-flux balance across the streamtube emanating from the jet hole, and it is found to vary slowly in the streamwise direction. The data are compared with Reynolds-Averaged Navier-Stokes simulations with standard k ε closure and an optimal turbulent Schmidt number. The computations underestimate the strength of the counter-rotating vortex pair, due to an overestimated eddy viscosity. On the other hand the entrainment is increasingly underpredicted downstream of injection. To capture the correct macroscopic trends, eddy viscosity and eddy diffusivity should vary spatially in different ways. Therefore a constant turbulent Schmidt number formulation is inadequate for this flow.
|Original language||English (US)|
|Number of pages||12|
|Journal||International Journal of Heat and Fluid Flow|
|State||Published - Oct 2013|
Bibliographical noteFunding Information:
The work of the first author was supported by the Honeywell Corporation. Use of the facilities at the Richard M. Lucas Center for Magnetic Resonance Spectroscopy and Imaging is gratefully acknowledged. The help of Lester K. Su during the PIV measurement campaign was greatly appreciated. In addition, this study was supported in part by the U.S. Army Research Office under contract/Grant number 57392-EG-II . The views expressed herein are those of the authors and do not purport to reflect the position of the Department of the Army, or the Department of Defense.
- Film cooling
- Jet in crossflow
- Turbulent diffusivity
- Turbulent mixing