Numerical simulations of stratiform boundary-layer clouds on the meso-γ-scale. Part II: The influence of a step change in surface roughness and surface temperature

1988 ◽  
Vol 44 (3) ◽  
pp. 207-230 ◽  
Author(s):  
Michael Tjernström
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Surface Temperature ◽  
Numerical Simulations ◽  
Step Change ◽  
Boundary Layer Clouds

scholarly journals Reply to: "Tropical cirrus and water vapor: an effective Earth infrared iris feedback?"

2002 ◽  
Vol 2 (2) ◽  
pp. 99-101 ◽  
Author(s):  
M.-D. Chou ◽  
R. S. Lindzen ◽  
A. Y. Hou
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Water Vapor ◽  
Surface Temperature ◽  
Climate Sensitivity ◽  
Physical Meaning ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Boundary Layer Clouds ◽  
High Level

Abstract. In assessing the iris effect suggested by Lindzen et al. (2001), Fu et al. (2002) found that the response of high-level clouds to the sea surface temperature had an effect of reducing the climate sensitivity to external radiative forcing, but the effect was not as strong as LCH found. The approach of FBH to specifying longwave emission and cloud albedos appears to be inappropriate, and the derived cloud optical properties may not have real physical meaning. The cloud albedo calculated by FBH is too large for cirrus clouds and too small for boundary layer clouds, which underestimates the iris effect.

Calculation of a Turbulent Boundary Layer Downstream of a Step Change in Surface Temperature

1979 ◽  
Vol 101 (1) ◽  
pp. 144-150 ◽  
Author(s):  
L. W. B. Browne ◽  
R. A. Antonia
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Prandtl Number ◽  
Surface Temperature ◽  
Reynolds Shear Stress ◽  
Turbulent Viscosity ◽  
Step Change ◽  
Mean Temperature ◽  
Thermal Layer ◽  
Good Agreement

Mean temperature and heat flux distributions in a thermal layer that develops within a momentum boundary layer subjected to a step change in surface temperature are calculated using two different methods. The method of Bradshaw and Unsworth, which uses the method of Bradshaw, Ferriss and Atwell to determine the mean velocity and Reynolds shear stress distributions and then assumes a constant turbulent Prandtl number for the heat flux calculation, yields heat flux distributions that are significantly different than the available experimental results at small distances from the step. Good agreement between calculations and experimental values is achieved when the distance x from the step is about 20 δ0, where δ0 is the boundary layer thickness at the step. To obtain good agreement with measurements of heat flux and mean temperature near the step, estimated distributions of turbulent viscosity and effective Prandtl number have been derived using an iterative updating procedure and the calculation method of Patankar and Spalding. These distributions are compared with those available in the literature. Calculated heat flux distributions show that the internal thermal layer is only likely to reach self-preserving conditions when x exceeds 40 δ0.

Heat Transfer in the Turbulent Boundary Layer With a Step Change in Surface Roughness

1991 ◽  
Author(s):  
Robert P. Taylor ◽  
J. Keith Taylor ◽  
M. H. Hosni ◽  
Hugh W. Coleman
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Smooth Surface ◽  
Plate Boundary ◽  
Step Change ◽  
Stanton Number ◽  
Test Surface ◽  
Temperature Profiles ◽  
Boundary Layer Flows

Measurements of Stanton numbers, velocity profiles, temperature profiles, and turbulence intensity profiles are reported for turbulent flat plate boundary layer flows with a step change in surface roughness. The first 0.9 m length of the test surface is roughened with 1.27 mm diameter hemispheres spaced 2 base diameters apart in a staggered array. The remaining 1.5 m length is smooth. The experiments show that the step change from a rough to a smooth surface has a dramatic effect on the convective heat transfer. In many cases, the Stanton number drops below the smooth-wall correlation immediately downstream of the change in roughness. The Stanton number measurements are compared with predictions using the discrete element method with excellent results.

Buoyancy Effects on a Boundary Layer Along an Infinite Cylinder With a Step Change of Surface Temperature

1983 ◽  
Vol 105 (1) ◽  
pp. 96-101 ◽  
Author(s):  
L. S. Yao
Keyword(s):  
Boundary Layer ◽  
Free Convection ◽  
Surface Temperature ◽  
Forced Convection ◽  
Leading Edge ◽  
Step Change ◽  
Convection Boundary Layer ◽  
Stagnation Line ◽  
Convection Boundary ◽  
Free Convection Boundary Layer

The laminar boundary layer induced by a horizontal forced flow along an infinite vertical cylinder with a step change of surface temperature is studied by a finite-difference method. Close to the thermal leading edge, the buoyancy force induces a strong free-convection boundary layer. Slightly above the thermal leading edge, the boundary layer starts to separate at the rear stagnation line (φ = 180 deg). The region of separated flow grows toward the forward stagnation line and becomes stationary at φ = 104 deg as one moves upward. In other words, free convection dominates the heat transfer along the thermal leading edge. The importance of forced convection increases as one moves vertically from the thermal leading edge and eventually becomes the dominant mode. The numerical results show that the free-convection boundary layer is suppressed at the forward stagnation line and is carried toward the rear stagnation line by the forced convection. The phenomenon shares many similarities with a thermal plume affected by forced convection.

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