Heat transfer enhancement by delta-wing vortex generators on a flat plate: Vortex interactions with the boundary layer

Experimental measurements of flow and heat transfer in a concave surface boundary layer in the presence of streamwise counter-rotating Görtler vortices show conclusively that local surface heat-transfer rates can exceed that of the turbulent flat-plate boundary layer even in the absence of turbulence. We have observed unexpected heat-transfer behavior in a laminar boundary layer on a concave wall even at low nominal velocity, a configuration not studied in the literature: The heat-transfer enhancement is extremely high, well above that corresponding to a turbulent boundary layer on a flat plate. To quantify the effect of freestream velocity on heat-transfer intensification, two criteria are defined for the growth of the Görtler instability: Pz for primary instability and Prms for the secondary instability. The evolution of these criteria along the concave surface boundary layer clearly shows that the secondary instability grows faster than the primary instability. Measurements show that beyond a certain distance the heat-transfer enhancement is basically correlated with Prms, so that the high heat-transfer intensification at low freestream velocities is due to the high growth rate of the secondary instability. The relative heat-transfer enhancement seems to be independent of the nominal velocity (global Reynolds number) and allows predicting the influence of the Görtler instabilities in a large variety of situations.

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Mechanism of Heat-Transfer Enhancement by Longitudinal Vortices in a Flat-Plate Boundary Layer.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.60.997 ◽

1994 ◽

Vol 60 (571) ◽

pp. 997-1004

Author(s):

Kahoru Torii ◽

Koichi Nishino ◽

Ken Nakayama

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Flat Plate ◽

Heat Transfer Enhancement ◽

Plate Boundary ◽

Transfer Enhancement ◽

Longitudinal Vortices ◽

Flat Plate Boundary Layer

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Comparison of Wing-Type Vortex Generators for Heat Transfer Enhancement in Channel Flows

Journal of Heat Transfer ◽

10.1115/1.2911462 ◽

1994 ◽

Vol 116 (4) ◽

pp. 880-885 ◽

Cited By ~ 105

Author(s):

St. Tiggelbeck ◽

N. K. Mitra ◽

M. Fiebig

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Delta Wing ◽

Local Heat Transfer ◽

Local Heat ◽

Vortex Generators ◽

Transfer Enhancement ◽

Transfer Coefficients ◽

Number Range ◽

Longitudinal Vortices

Longitudinal vortices can be generated in a channel flow by punching or mounting small triangular or rectangular pieces on the channel wall. Depending on their forms, these vortex generators (VG) are called delta wing, rectangular wing, pair of delta winglets, and pair of rectangular winglets. The heat transfer enhancement and the flow losses incurred by these four basic forms of VGs have been measured and compared in the Reynolds number range of 2000 to 9000 and for angles of attack between 30 and 90 deg. Local heat transfer coefficients on the wall have been measured by liquid crystal thermography. Results show that winglets perform better than wings and a pair of delta winglets can enhance heat transfer by 46 percent at Re=2000 to 120 percent at Re=8000 over the heat transfer on a plate.

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Heat transfer enhancement downstream of vortex generators on a flat plate

10.31274/rtd-180813-6870 ◽

1984 ◽

Author(s):

Aly Youssef Turk

Keyword(s):

Heat Transfer ◽

Flat Plate ◽

Heat Transfer Enhancement ◽

Vortex Generators ◽

Transfer Enhancement

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Heat Transfer Enhancement by Delta-Wing-Generated Tip Vortices in Flat-Plate and Developing Channel Flows

Journal of Heat Transfer ◽

10.1115/1.1513578 ◽

2002 ◽

Vol 124 (6) ◽

pp. 1158-1168 ◽

Cited By ~ 79

Author(s):

M. C. Gentry ◽

A. M. Jacobi

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Flat Plate ◽

Heat Transfer Enhancement ◽

Channel Flow ◽

Delta Wing ◽

Leading Edge ◽

Transfer Enhancement ◽

Transfer Coefficients ◽

Vortex Strength

Using delta wings placed at the leading edge of a flat plate, streamwise vortices are generated that modify the flow; the same wings are also used to modify a developing channel flow. Local and average measurements of convection coefficients are obtained using naphthalene sublimation, and the structure of the vortices is studied using flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement of the channel flow is also investigated. In regions where a vortex induces a surface-normal inflow, the local heat transfer coefficients are found to increase by as much as 300 percent over the baseline flow, depending on vortex strength and location relative to the boundary layer. Vortex strength increases with Reynolds number, wing aspect ratio, and wing attack angle, and the vortex strength decays as the vortex is carried downstream. Considering the complete channel surface, the largest spatially averaged heat average heat transfer enhancement is 55 percent; it is accompanied by a 100 percent increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator.

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Large Eddy Simulation of Turbulent Flow and Heat Transfer Characteristics in Rectangle Channel With Vortex Generators

2010 14th International Heat Transfer Conference, Volume 1 ◽

10.1115/ihtc14-22072 ◽

2010 ◽

Author(s):

Juan Wen ◽

Li Yang ◽

Cheng Ying Qi

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Heat Transfer Enhancement ◽

Coherent Structure ◽

Vortex Generator ◽

Vortex Generators ◽

Transfer Enhancement ◽

Heat Transfer Characteristics ◽

Eddy Simulation ◽

Large Eddy

The flow structures and heat transfer characteristics of rectangle channel with the new type of vortex generators are obtained using large eddy simulation (LES) and by the application of the hydromechanics software FLUENT6.3. The bevel-cut half-elliptical column vortex generators, which is one model of the passive heat transfer enhancement, are laid on the three-dimensional rectangle channel. The instantaneous characteristic and the variational law of various parameters, such as the velocity, the temperature, the pressure and the vorticity magnitude, is analyzed to find out the temperature stripe structure that is similar with the velocity stripe in the temperature field. A turbulent boundary layer interacting with the disturbance of the vortex generators, is investigated using a “coherent structure” type of approach. The coherent structure and the streak structure of turbulent boundary layer flow are showed and the characteristic of vortex induced by vortex generator and its influence on turbulent coherent structure are analyzed. The control of the coherent structure induced by vortex generator plays more important role in heat transfer enhancement and drag reduction. And this fow configuration is of interest in terms of both heat transfer and skin friction control. The result of simulation indicates that the turbulence coherent structure directly affects the temperature gradient at the wall and the heat transfer enhancement mechanism of vortex generator is explained. Then we can seek suitable form of vortex generator and structure parameters, in order to achieve enhanced heat transfer and flow of drag reduction.

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