Swirl-Enhanced Internal Cooling of Turbine Airfoils: Part II—90 Degree Flow Entry

2011 ◽  
Author(s):  
Del Segura ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
High Velocity ◽  
Flow Direction ◽  
Jet Flow ◽  
Main Channel ◽  
Positive Pressure ◽  
Slot Channel ◽  
Lower Velocity ◽  
Flow Through

Heat transfer measurements and analysis have been performed on a uniquely designed multi-channel passage consisting of a slot shaped channel with a 3:1 aspect ratio with coolant-feed tubes located adjacent to the main slot shaped channel. Small round jets connect the outer feed passages to the main channels at a 15 degree angle relative to the main channel flow direction and at a position tangent to the floor/roof of the main channel. Flow entering the multi-channel passages is directed into the main channel through orifices that reduce the pressure in the main channel, thereby enabling positive pressure differences between the feed and the main channel and allowing high velocity flow through the jets. The flow enters the main channel via a 90-degree turn through the orifice. The resulting flow through the side jets and main channel causes high shear flow along the roof and floor of the channel where the jet flow enters the main channel, swirl motion as the high velocity side jet flow enters the main channel flow at an angle relative to the main flow direction, and high turbulence regions as the lower velocity main channel flow tumbles when coming in contact with the high velocity jets issuing from the side channels. The heat transfer characteristics were compared to the slot channel with a 90 degree inlet with no additional heat transfer enhancements. Four different jet configurations are presented along with three different orifice diameters. While a single channel passage with flow exiting freely is not a design typically found in a turbine airfoil, the benefits of this unique concept can be a basis for further studies with geometries more typical of a production airfoil. The results yield average normalized Nusselt numbers enhancement for the entire main channel as high as 10.7, when compared to a smooth slot channel without heat transfer enhancements. Pressure losses, mainly due to the orifices, were high but the overall performance shows significant improvements when compared to other heat transfer enhancement methods in turbine airfoil mid-span regions.

Optimization of Fin Performance in a Laminar Channel Flow Through Dimpled Surfaces

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Carlos Silva ◽  
Doseo Park ◽  
Egidio (Ed) Marotta ◽  
Leroy (Skip) Fletcher
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Investigation ◽  
Channel Flow ◽  
Heat Load ◽  
Pressure Losses ◽  
Thermal Improvement ◽  
Laminar Channel Flow ◽  
Flow Through ◽  
The Heat Transfer Coefficient

The effect of the dimple shape and orientation on the heat transfer coefficient of a vertical fin surface was determined both numerically and experimentally. The investigation focused on the laminar channel flow between fins, with a Re=500 and 1000. Numerical simulations were performed using a commercial computational fluid dynamics code to analyze optimum configurations, and then an experimental investigation was conducted on flat and dimpled surfaces for comparison purposes. Numerical results indicated that oval dimples with their “long” axis oriented perpendicular to the direction of the flow offered the best thermal improvement, hence the overall Nusselt number increased up to 10.6% for the dimpled surface. Experimental work confirmed these results with a wall-averaged temperature reduction of up to 3.7K, which depended on the heat load and the Reynolds number. Pressure losses due to the dimple patterning were also briefly explored numerically in this work.

Heat Transfer Enhancement by Synthetic Jet Arrays in Air-Cooled Heat Sinks for Use in Electronics Cooling

2012 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Min Zhang ◽  
Youmin Yu ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Sink ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A synthetic jet is an intermittent jet which issues through an orifice from a closed cavity over half of an oscillation cycle. Over the other half, the flow is drawn back through the same orifice into the cavity as a sink flow. The flow is driven by an oscillating diaphragm, which is one wall of the cavity. Synthetic jets are widely used for heat transfer enhancement since they are effective in disturbing and thinning thermal boundary layers on surfaces being cooled. They do so by creating an intermittently-impinging flow and by carrying to the hot surface turbulence generated by breakdown of the shear layer at the jet edge. The present study documents experimentally and computationally heat transfer performance of an array of synthetic jets used in a heat sink designed for cooling of electronics. This heat sink is comprised of a series of longitudinal fins which constitute walls of parallel channels. In the present design, the synthetic jet flow impinges on the tips of the fins. In the experiment, one channel of a 20-channel heat sink is tested. A second flow, perpendicular to the jet flow, passes through the channel, drawn by a vacuum system. Surface- and time-averaged heat transfer coefficients for the channel are measured, first with just the channel flow active then with the synthetic jets added. The purpose is to assess heat transfer enhancement realized by the synthetic jets. The multiple synthetic jets are driven by a single diaphragm which, in turn, is activated by a piezoelectrically-driven mechanism. The operating frequency of the jets is 1250 Hz with a cycle-maximum jet velocity of 50 m/s, as measured with a miniature hot-film anemometer probe. In the computational portion of the present paper, diaphragm movement is driven by a piston, simulating the experimental conditions. The flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. Computed heat transfer coefficients show a good match with experimental values giving a maximum difference of less than 10%. The effects of amplitude and frequency of the diaphragm motion are documented. Changes in heat transfer due to interactions between the synthetic jet flow and the channel flow are documented in cases of differing channel flow velocities as well as differing jet operating conditions. Heat transfer enhancement obtained by activating the synthetic jets can be as large as 300% when the channel flow is of a low velocity compared to the synthetic jet peak velocity (as low as 4 m/s in the present study).

Enhancement of Heat Transfer of Mixing Convection in a Vertical Channel by a Moving Block

2013 ◽  
Vol 29 (1) ◽  
pp. 95-107 ◽  
Author(s):  
W.-S. Fu ◽  
J.-C. Huang ◽  
Y.-Y. Wang ◽  
Y. Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Vertical Channel ◽  
Convection Flow ◽  
Enhancement Of Heat Transfer ◽  
Lower Velocity ◽  
Lower Magnitude

AbstractEnhancement of a heat transfer rate of mixed convection flow in a three-dimensional vertical channel with insertion of a moving slender block is investigated numerically. A slender block is installed along the direction of the channel flow, and the movement of the slender block is in periodic motion and transverse to the channel flow. The interaction between the moving block and the channel flow destroys and suppresses the velocity and thermal boundary layers on the heat surface periodically. Various ratios of the Richardson numbers (Gr/Re2) are simulated. The results show that under a higher velocity of the channel flow and a lower magnitude of Gr/Re2, the enhancement of heat transfer rate is better. Oppositely, under a lower velocity of the channel flow and a higher magnitude of Gr/Re2, the effect of natural convection driven by the buoyancy force is stronger and it is unfavorable to the heat transfer. A counter effect of the heat transfer rate is observed. These phenomena which are seldom analyzed before by numerical simulation are carried out in this study.

Effects of Free-Stream Turbulence on the Instantaneous Heat Transfer in a Wall Jet Flow

1997 ◽  
Vol 119 (2) ◽  
pp. 359-363 ◽  
Author(s):  
S. Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Flow Direction ◽  
Vertical Direction ◽  
Jet Flow ◽  
Wall Jet ◽  
Axial Component ◽  
Free Stream Turbulence ◽  
Wall Jet Flow ◽  
Hot Film

This is a preliminary study in order to understand how free-stream turbulence increases heat transfer. Effects of free-stream turbulence on instantaneous heat transfer were investigated in a wall jet flow. Heat transfer traces obtained by a hot-film probe flush-mounted with the surface showed an intermittent structure with definite peaks at certain time intervals. The number of peaks per unit time increased with increasing turbulence intensity. A wall jet test rig was designed and built. The initial thickness and the velocity of the wall jet were 10 cm and 24.4 m/s, respectively. The hot-film probe, which was flush with the surfaces, was positioned at 10 cm intervals on the surface in the flow direction. The profiles of mean velocity and axial component of the Reynolds stress were measured with a horizontal hot-wire probe. Space correlation coefficients for u′ and q′ were obtained in the vertical direction to the wall. This paper concentrates on the effects of turbulence level on instantaneous heat transfer at the wall. It is speculated that the intermittent structures of the heat transfer traces are related to burst phenomena and increase in heat transfer is due to increased ejections (bursts) at the wall with increasing turbulence levels.

scholarly journals Effects of Free Stream Turbulence on the Instantaneous Heat Transfer in a Wall Jet Flow

1995 ◽  
Author(s):  
Savash Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Flow Direction ◽  
Vertical Direction ◽  
Jet Flow ◽  
Wall Jet ◽  
Axial Component ◽  
Free Stream Turbulence ◽  
Wall Jet Flow ◽  
Hot Film

This is a preliminary study in order to understand how free stream turbulence increases the heat transfer. Effects of free stream turbulence on the instantaneous heat transfer were investigated in a wall jet flow. Heat transfer traces obtained by a hot film probe flush-mounted with the surface showed an intermittent structure with definite peaks at certain time intervals. Number of peaks per unit time increased with increasing turbulence intensity. A wall jet test rig was designed and built. The initial thickness and the velocity of the wall jet were 10 cm and 24.4 m/s respectively. The hot film probe which was flush with the surfaces was positioned at 10 cm intervals on the surface in the flow direction. The profiles of mean velocity and axial component of the Reynolds stress were measured with a horizontal hot wire probe. Space correlation coefficients for u′ and q′ were obtained in the vertical direction to the wall. This paper concentrates on the effects of turbulence level on the instantaneous heat transfer at the wall. It is speculated that intermittent structure of the heat transfer traces are related to burst phenomena and increase in heat transfer is due to increased ejections (bursts) at the wall with increasing turbulence levels.

scholarly journals Optimal Patterned Wettability for Microchannel Flow Boiling Using the Lattice Boltzmann Method

Coatings ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 288 ◽  
Author(s):  
Young Wi ◽  
Jong Kim ◽  
Jung Lee ◽  
Joon Lee
Keyword(s):  
Heat Transfer ◽  
Lattice Boltzmann Method ◽  
Channel Flow ◽  
Lattice Boltzmann ◽  
Flow Boiling ◽  
Flow Direction ◽  
Bubble Nucleation ◽  
Microchannel Flow ◽  
Pattern Length ◽  
Boltzmann Method

Microchannel flow boiling is a cooling method studied in microscale heat-cooling, which has become an important field of research with the development of high-density integrated circuits. The change in microchannel surface characteristics affects thermal fluid behavior, and existing studies have optimized heat transfer by changing surf ace wettability characteristics. However, a surface with heterogeneous wettability also has the potential to improve heat transfer. In this case, heat transfer would be optimized by applying the optimal heterogeneous wettability surface to channel flow boiling. In this study, a change in cooling efficiency was observed, by setting a hydrophobic and hydrophilic wettability pattern on the channel surface under the microchannel flow boiling condition, using a lattice Boltzmann method simulation. In the rectangular microchannel structure, the hydrophobic-hydrophilic patterned wettability was oriented perpendicular to the flow direction. The bubble nucleation and the heat transfer coefficient were observed in each case by varying the length of the pattern and the ratio of the hydrophobic-hydrophilic area. It was found that the minimum pattern length in which individual bubbles can occur, and the wettability pattern in which the bubble nucleation-departure cycle is maintained, are advantageous for increasing the efficiency of heat transfer in channel flow boiling.

Heat Transfer Enhancement in Channel Flow Using an Inclined Square Cylinder

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Dong-Hyeog Yoon ◽  
Kyung-Soo Yang ◽  
Choon-Bum Choi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Large Scale ◽  
Channel Wall ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Square Cylinder ◽  
Transfer Enhancement

Heat transfer enhancement in channel flow by using an inclined vortex generator has been numerically investigated. A square cylinder is located on the centerline of laminar channel flow, which is subject to a constant heat flux on the lower channel wall. As the cylinder is inclined with some angle of attack with respect to the main flow direction, flow characteristics change downstream of the cylinder, and significantly affect heat transfer on the channel wall. A parametric study has been conducted to identify the cause, and to possibly find the optimal inclination angle. It turns out that the increased periodic fluctuation of the vertical velocity component in the vicinity of the channel walls is responsible for the heat transfer enhancement. The large fluctuation is believed to be induced by the large-scale vortices shed from the inclined square cylinder, as well as by the secondary vortices formed near the channel walls.

Effect of Bleed Position and Bleed Angle on Impingement Cooling of a Spherical-Dimpled Surface

2016 ◽  
Author(s):  
Zhao Liu ◽  
Xing Yang ◽  
Jun Li ◽  
Zhenping Feng ◽  
Terrence Simon
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Flow Rate ◽  
Film Cooling ◽  
Lower Surface ◽  
Jet Flow ◽  
Surface Cooling ◽  
Impingement Jet ◽  
Purge Flow ◽  
Bottom Side

Numerical simulations were performed to document cooling of the lower surface of a channel. Through the channel top wall and normal to the channel flow are cooling jets that impinge on the channel lower surface. This surface has a regular array of dimples with centers in line with the impingement jet axes. Also on the channel lower surface is a series of purge holes through which coolant flow is extracted. The effects of location of the purge holes relative to the dimples and angle of the purge holes on the channel lower surface cooling performance are documented. A 3D RANS analysis with SST k-ω turbulence closure modeling was conducted with a Reynolds number of the impingement jet of 35,000. The position of the purge hole relative to the dimple was varied from −0.34 to 0.50 dimple spacing, the purge hole angle varied as 30° and 150° and three different ratios of bleed flow rate to impingement jet flow rate, 2.5%, 5.0% and 12.0%, were documented. The results show how the combined effects of impingement jet flow, channel crossflow and purge flow affect heat transfer characteristics on the channel lower surface for this assembly. Also shown is how the dimpled surface heat transfer benefits from putting the purge flow holes slightly upstream in the channel flow from the dimples. The geometry under study may be applied for cooling a gas turbine endwall, where the bottom side of the channel lower wall of the assembly under study would be the passage endwall and the purge flow would be discrete hole film cooling flow.

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