Mixed Convection Along a Semi-Infinite Vertical Flat Plate With Uniform Surface Heat Flux

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
S. Ghosh Moulic ◽  
L. S. Yao
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Leading Edge ◽  
Surface Heat ◽  
Convection Boundary Layer ◽  
Edge Region ◽  
Local Skin ◽  
Convection Boundary ◽  
Local Skin Friction ◽  
Vertical Flat Plate

Mixed-convection boundary-layer flow over a heated semi-infinite vertical flat plate with uniform surface heat flux, placed in a uniform isothermal upward freestream, has been investigated. Near the leading edge, the effect of natural convection can be treated as a small perturbation term. The effects of natural convection are accumulative and increase downstream. In the second region, downstream of the leading-edge region, natural convection eventually becomes as important as forced convection. The boundary-layer equations have been solved by an adaptive finite-difference marching technique. The numerical solution indicates that the series solution of the leading-edge region is included in that of the second region. This property is shared by many developing flows. However, the series solutions of local similarity or local nonsimilarity are only valid for very small distances from the leading edge. Numerical results for the local skin-friction factor, wall temperature, and local Nusselt number are presented for Pr=1 for a wide range of Grx*∕Rex5∕2, where Grx* is a local modified Grashof number and Rex is a local Reynolds number. The results indicate that cfxRex1∕2 and NuxRex–1∕2 increase monotonically with distance from the leading edge, where cfx is the local skin-friction factor and Nux is the local Nusselt number, and approach the free-convection limit at large values of Grx*∕Rex5∕2, although the velocity distribution differs from the velocity distribution in a free-convection boundary layer.

The manipulation of the streamwise vortex instability in a natural convection boundary layer along a heated inclined flat plate

2002 ◽  
Vol 470 ◽  
pp. 31-61 ◽  
Author(s):  
MARK A. TRAUTMAN ◽  
ARI GLEZER
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Natural Convection ◽  
Surface Temperature ◽  
Streamwise Vortex ◽  
Surface Heat ◽  
Convection Boundary Layer ◽  
Water Tank ◽  
Surface Heat Transfer ◽  
Convection Boundary

Flow instabilities leading to the formation of streamwise vortices in a natural convection boundary layer over a heated inclined plate submerged in a water tank are manipulated using spanwise arrays of surface-mounted heating elements. The flow over the plate is driven by a two-ply surface heater comprised of a uniform, constant- heat flux heater and a mosaic of 32 × 12 individually controlled heating elements that are used as control actuators. Surface temperature distributions are measured using liquid crystal thermography and the fluid velocity in cross-stream planes is measured using particle image velocimetry (PIV). Time-invariant spanwise-periodic excitation over a range of spanwise wavelengths leads to the formation of arrays of counter-rotating streamwise vortex pairs and to substantial modification of the surface temperature and heat transfer. The increase in surface heat transfer is accompanied by increased entrainment of ambient fluid and, as a consequence, higher streamwise flowrate. Subsequent spanwise-periodic merging of groups of vortices farther downstream retards the streamwise increase of the surface heat transfer rate. Finally, the suppression of small-amplitude spanwise disturbances by linear cancellation is demonstrated.

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