Stagnation Flow and Heat Transfer From a Finite Disk Situated Perpendicular to a Uniform Stream

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Stefan aus der Wiesche ◽  
Christian Helcig

Abstract The stagnation flow and heat transfer from the blunt surface of a finite circular disk subjected to a uniform stream of an incompressible fluid is revisited in this paper. A laminar boundary layer analyses were carried out employing the method developed by Frössling. The involved auxiliary functions were calculated for several Prandtl numbers. It was found that the exact knowledge of the velocity at the outer edge of the boundary layer was essential to achieve an accurate velocity solution. In addition to the analytical work, computational fluid dynamics (CFD) simulations and a detailed experimental study were conducted including heat transfer measurements in a wind tunnel and a large water towing tank. The analytical treatment enabled a clear discussion of the effect of the Prandtl number on convective heat transfer from a blunt disk. A primary effect and a secondary effect were distinguished based on the analytical treatment. The boundary layer theory offered a rather efficient calculation method, and its results were in an excellent agreement with experimental data.

Author(s):  
Stefan aus der Wiesche

Abstract The stagnation flow and heat transfer from the blunt surface of a finite circular disk subjected to a uniform stream of an incompressible fluid is revisited in this paper. A laminar boundary layer analyses was carried out employing the method developed by Frössling. The involved auxiliary functions were calculated for several Prandtl numbers. It was found that the exact knowledge of the velocity at the outer edge of the boundary layer was essential to achieve an accurate velocity solution. In addition to the analytical work, computational fluid dynamics (CFD) simulations and an experimental study were carried out. The analytical treatment enabled a clear discussion of the effect of the Prandtl number on convective heat transfer from a blunt disk. A primary and a secondary effect were distinguished based on the rigorous analytical treatment. The boundary layer theory offered a rather efficient calculation method, and its results were in an excellent agreement with available literature data.


Author(s):  
X. Liu ◽  
W. Rodi

A detailed experimental study has been conducted on the wake-induced unsteady flow and heat transfer in a linear turbine cascade. The unsteady wakes with passing frequencies in the range zero to 240 Hz were generated by moving cylinders on a squirrel cage device. The velocity fields in the blade-to-blade flow and in the boundary layers were measured with hot-wire anemometers, the surface pressures with a pressure transducer and the heat transfer coefficients with a glue-on hot film. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar on the pressure side in all cases and in the case without wakes also on the suction side. On the latter, the wakes generated by the moving cylinders caused transition, and the beginning of transition moves forward as the cylinder-passing frequency increases. Unlike in the flat-plate study of Liu and Rodi (1991a) the instantaneous boundary layer state does not respond to the passing wakes and therefore does not vary with time. The heat transfer increases under increasing cylinder-passing frequency even in the regions with laminar boundary layers due to the increased background turbulence.


Author(s):  
Pawan K. Singh ◽  
Hua Feng Samuel Tan ◽  
Chiang Juay Teo ◽  
Poh Seng Lee

The Wavy channels are supposed to enhance performance of microchannel heat sink through chaotic advection. The change in boundary layer thickness (thinning) and the macroscopic mixing due to the formation of Dean’s vortices have been found to be main reasons for enhanced heat transfer in wavy microchannel. Present study carries out a detailed numerical investigation for flow and heat transfer in wavy channel. A 3D geometry for a single loop of wavy channel is modeled in GAMBIT and simulated in CFD software FLUENT. The basic dimensions were 0.15 mm width, 0.3 mm height and 1.5 mm length. The formation of Dean vortices are shown. In parametric study, the effect of Re number on the flow and heat transfer performance is shown. Heat transfer was found to be increased with Re. The effect of Aspect ratio is shown. The channel with the aspect ratio of 0.5 is found to be best among the channels studied including wavy and straight microchannels. A novel concept of secondary branches is introduced to wavy microchannel to take advantage of high pressure zone at crust. The branched wavy microchannel encouraged the secondary flow thus enhanced the macroscopic mixing. Due to disrupt of boundary layer development and its re-initialization, an improved thermal performance was achieved.


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