Affiliation:
1. Department of Mechanical Engineering, Clemson University, Clemson, SC 29634-0921
Abstract
The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. The acceleration parameter, K, was kept constant along the test section. Both surface heat transfer and boundary layer measurements were conducted. The boundary layer measurements were conducted with a three-wire probe (two velocity wires and one temperature wire) for two representative cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The surface heat transfer measurements were conducted for K values ranging from −0.045 × 10−6 to −1.44 × 10−6 over five divergent wall angles. The Stanton numbers of the cases with adverse pressure gradients were greater than that of the zero-pressure-gradient turbulent correlation in the low-Reynolds-number turbulent flow, and the difference increased as the adverse pressure gradient was increased. The adverse pressure gradient caused earlier transition onset and shorter transition length based on Rex, Reδ*, and Reθ in comparison to zero-pressure-gradient conditions. As expected, there was a reduction in skin friction as the adverse pressure gradient increased. In the U+−Y+ coordinates, the adverse pressure gradients had a significant effect on the mean velocity profiles in the near-wall region for the late-laminar and early transition stations. The mean temperature profile was observed to precede the velocity profile in starting and ending the transition process, opposite to what occurred in favorable pressure gradient cases in previous studies. A curve fit of the turbulent temperature profile in the log-linear region for the K2 case gave a conduction layer thickness of Y+ = 9.8 and an average Prt = 0.71. In addition, the wake region of the turbulent mean temperature profile was significantly suppressed.
Reference33 articles.
1. Abu-Ghannam B. J. , and ShawR., 1980, “Natural Transition of Boundary Layers—The Effects of Turbulence, Pressure Gradient, and Flow History,” Journal of Mech. Engr. Science, Vol. 22, No. 5, pp. 213–228.
2. Acharya, M., 1985, “Pressure-Gradient and Free-Stream Turbulence Effects on Boundary-Layer Transition,” Brown Boveri Research Center, Baden, Switzerland, Rept. KLR 85-127C.
3. Blackwell, B. F., Kays, W. M., and Moffat, R. J., 1972, “The Turbulent Boundary Layer on a Porous Plate: An Experimental Study of the Heat Transfer Behavior with Adverse Pressure Gradients,” Report No. HMT-16, Thermosciences Division, Department of Mechanical Engineering, Stanford University.
4. Brown A. , and MartinB. W., 1976, “The Use of Velocity Gradient Factor as a Pressure Gradient Parameter,” Proc. IMechE, Vol. 190, pp. 277–285.
5. Clauser F. H. , 1954, “Turbulent Boundary Layers in Adverse Pressure Gradients,” Journal of the Aeronautical Sciences, Vol. 21, pp. 91–108.
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