Concavity Enhanced Heat Transfer in an Internal Cooling Passage

1997 ◽  
Author(s):  
M. K. Chyu ◽  
Y. Yu ◽  
H. Ding ◽  
J. P. Downs ◽  
F. O. Soechting
Keyword(s):  
Heat Transfer ◽  
Imaging System ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Pressure Losses ◽  
Turbine Cooling ◽  
Rib Turbulators ◽  
Cooling Passage

The present study evaluates an innovative approach for enhancement of surface heat transfer in a channel using concavities, rather than protruding elements. Serving as a vortex generator, a concavity is expected to promote turbulent mixing in the flow bulk and enhance the heat transfer. Using a transient liquid crystal imaging system, local heat transfer distribution on the surface roughened by an staggered array based on two different shapes of concavities, i.e. hemispheric and tear-drop shaped, have been obtained, analyzed and compared. The results reveal that both concavity configurations induce a heat transfer enhancement similar to that of continuous rib turbulators, about 2.5 times their smooth counterparts 10,000 ≤ Re ≤ 50,000. In addition, both concavity arrays reveal remarkably low pressure losses that are nearly one-half the magnitudes incurred with protruding elements. In turbine cooling applications, the concavity approach is particularly attractive in reducing system weight and ease of manufacturing.

Heat Transfer Enhancement and Pressure Loss Characteristics of Zig-Zag Channel With Dimples and Protrusions

2015 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Test Channel ◽  
Rib Turbulators ◽  
Cooling Passage

This paper described a detailed experimental study to explore an internal cooling passage that mimic a “zig-zag” pattern. There are four passages connected by 110° turning angle in a periodic fashion, hence the name. Experiments are performed in a scaled-up test channel with a cross-section of 63.5mm by 25.4mm, corresponding to the aspect ratio of 2.5:1. Compared to the conventional straight internal cooling passages, the zig-zag channel with several turns will generate additional secondary vortices while providing longer flow path that allows coolant to remove much more heat load prior to discharge into the hot mainstream. Surface features, (1) dimples, and (2) protrusions are added to the zig-zag channel to further enhance the heat transfer, while contributed to larger wetted area. The experiment utilizes the well-established transient liquid crystal technique to determine the local heat transfer coefficient distribution of the entire zig-zag channel. Protrusions exhibit higher heat transfer enhancement than that of dimples. However, both designs proved to be inferior compared to the rib-turbulators. Pressure loss in these test channels is approximately twofold higher than that of straight smooth test channel due to the presence of turns; but the pressure loss is lower than the zig-zag channel with rib-turbulators. The result revealed that one advantage of having either protrusions or dimples as these surface elements will resulted in gradual and more uniform increment of heat transfer throughout the entire channel compared to previous test cases.

The Influence of Including a Partially Smooth Section in the 2nd Leg of an Internally Ribbed Two Pass Cooling Channel

2006 ◽  
Author(s):  
Detlef Pape ◽  
Sean Jenkins ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand ◽  
Martin Schnieder
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Fluid Temperature ◽  
Turbine Engine ◽  
Pressure Losses ◽  
Uniform Manner

Internal cooling schemes for blades in a gas turbine engine often are subject to compromises between increased pressure losses in return for greater levels of heat transfer required to maintain durability levels in the engine’s harsh environment. Rib configurations have been the subject of much study in past years, however these configurations are normally presumed to be used in “full-coverage” mode, meaning that the ribs are placed in the channel in a continuous and uniform manner. This study investigates the interaction between the bend effects downstream of a 180° bend, which cause higher local heat transfer, and the effect of ribs. Some of the ribs directly downstream of the 180° bend in the 2nd leg of a two pass high aspect ratio (4:1) channel were removed and the effect on heat transfer was assessed. Experimental results showed that the heat transfer level recovered quickly once ribs were encountered. As expected, some decrease in heat transfer was observed in the region where ribs were removed; however total pressure losses in the channel were also much lower. Results include detailed two-dimensional heat transfer distributions determined by the transient liquid crystal method as well as an analysis of the balance between pressure recovery and local heat transfer levels. Generally, for the accuracy of the transient liquid crystal technique in complex three-dimensional flows, strongly varying fluid temperatures present in and downstream of the bend region must be taken into account. For this study, time and position dependent fluid temperature distributions were measured to account for these effects, making it possible to obtain high quality heat transfer results in those regions.

Influence of Rotation on Heat Transfer in a Two-Pass Channel With Impingement Under High Reynolds Number

2015 ◽  
Author(s):  
Li Yang ◽  
Kartikeya Tyagi ◽  
Srinath Ekkad ◽  
Jing Ren
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Coriolis Force ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Channel Diameter ◽  
Turbine Cooling ◽  
High Reynolds ◽  
The Impact

Effect of rotation on turbine blade internal cooling is an important factor in gas turbine cooling systems. In order to minimize the impact from the Coriolis force, cooling structures with less rotation-dependent cooling effectiveness are needed. This study presents an impingement design in a two pass channel to reduce impact of rotational forces on non-uniform heat transfer behavior inside these complex channels. A Transient Liquid Crystal(TLC) method was employed to obtain local heat transfer coefficient measurements in a rotating environment. The channel Reynolds number based on the channel diameter ranges from 25,000 to 100,000. The rotation number ranges from 0 to 0.14. A series of computational simulations with the SST model were also utilized to understand the flow field behavior that impacts the heat transfer distributions on the walls. A 1-D correlation of zone averaged Nusselt number distribution was derived from the measurements. Results show that rotation reduces the heat transfer on both sides of the impingement, which is due to the Coriolis force and the pressure redistribution. The local change in the present study is about 25%. Rotation significantly enhances the heat transfer near the closed end because of the centrifugal force and the ‘pumping’ effect. Within the parameters of this test, the magnitude of enhancement is 25% to 75%. Compared to U-bended two pass channel, impingement channel has advantages in the upstream channel and the end region, but performance is not beneficial on the leading side of the downstream channel.

Large Eddy Simulation of Flow and Heat Transfer in a Channel Roughened by Square or Semicircle Ribs

2004 ◽  
Author(s):  
Joon Ahn ◽  
Haecheon Choi ◽  
Joon Sik Lee
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Scale Model ◽  
Internal Cooling ◽  
Ribbed Channel ◽  
Cold Fluid ◽  
Large Eddy ◽  
Cooling Passage

The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. So far, most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Round ribs have also been tested expecting that they may enhance the thermal and aerodynamic performance. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. Large eddy simulations (LES) of turbulent flow in a ribbed channel with a dynamic subgrid-scale model are performed. In our simulation, the no-slip and no-jump conditions on the rib surface are satisfied in Cartesian coordinates using an immersed boundary method. We have also conducted an experimental study to validate the simulation. The velocity and temperature fields are measured using hot wire and thermocouple, respectively. The surface heat transfer is measured using the thermochromic liquid crystal with a high spatial resolution. LES predicts the detailed flow and thermal features such as the turbulence intensity around the ribs and the local heat transfer distribution between the ribs, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms responsible for the local heat transfer distributions between the ribs; i.e. the entrainment of the cold fluid by the vortical motions and the impingement of the entrained cold fluid on the ribs. We also discuss the local heat transfer variation of the ribs in connection with flow separation and turbulent kinetic energy. The total drag and heat transfer are calculated and compared between the square and semicircle ribs, showing that two ribs produce nearly the same heat transfer, but the semicircle one yields lower drag than the square one.

Large Eddy Simulation of Flow and Heat Transfer in a Channel Roughened by Square or Semicircle Ribs

2005 ◽  
Vol 127 (2) ◽  
pp. 263-269 ◽  
Author(s):  
Joon Ahn ◽  
Haecheon Choi ◽  
Joon Sik Lee
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Scale Model ◽  
Internal Cooling ◽  
Ribbed Channel ◽  
Cold Fluid ◽  
Large Eddy ◽  
Cooling Passage

The internal cooling passage of a gas turbine blade has been modeled as a ribbed channel. In the present study, we consider two different rib geometries, i.e., square and semicircle ribs, in order to investigate their thermal and aerodynamic performance. Large eddy simulations (LESs) of turbulent flow in a ribbed channel with a dynamic subgrid-scale model are performed. In our simulation, the no-slip and no-jump conditions on the rib surface are satisfied in the Cartesian coordinates using an immersed boundary method. In order to validate the simulation results, an experimental study is also conducted, where the velocity and temperature fields are measured using a hot wire and a thermocouple, respectively, and the surface heat transfer is measured using the thermochromic liquid crystal. LES predicts the detailed flow and thermal features, such as the turbulence intensity around the ribs and the local heat transfer distribution between the ribs, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms responsible for the local heat transfer distribution between the ribs, i.e., the entrainment of the cold fluid by vortical motions and the impingement of the entrained cold fluid on the ribs. We also discuss the local variation of the heat transfer with respect to the rib geometry in connection with flow separation and turbulent kinetic energy. The total drag and heat transfer are calculated and compared between the square and semicircle ribs, showing that two ribs produce nearly the same heat transfer, but the semicircle one yields lower drag than the square one.

Heat Transfer Measurements to a Gas Turbine Cooling Passage With Inclined Ribs

1998 ◽  
Vol 120 (1) ◽  
pp. 63-69 ◽  
Author(s):  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler ◽  
J. W. Chew
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Scale Model ◽  
Turbine Cooling ◽  
Gas Turbine Cooling ◽  
Cooling Passage

The local heat transfer coefficient distribution over all four walls of a large-scale model of a gas turbine cooling passage have been measured in great detail. A new method of determine the heat transfer coefficient to the rib surface has been developed and the contribution of the rib, at 5 percent blockage, to the overall roughened heat transfer coefficient was found to be considerable. The vortex-dominated flow field was interpreted from the detailed form of the measured local heat transfer contours. Computational Fluid Dynamics calculations support this model of the flow and yield friction factors that agree with measured values. Advances in the heat transfer measuring technique and data analysis procedure that confirm the accuracy of the transient method are described in full.

Heat Transfer of a Chordwise-Oriented Internal Cooling Passage Around a Turbine Airfoil

2001 ◽  
Author(s):  
M. K. Chyu ◽  
O. B. Ojo ◽  
C. H. Yen ◽  
R. S. Nordlund
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Cooling Passage

Abstract An innovative design of closed-loop cooling system for a stator airfoil consists of a number of internal cooling passages wrapping around both pressure and suction sides of the airfoil. The cooling passages feature (1) jet impingement post a sharp 90-degree turn at the passage inlet, (2) turbulators on the outermost wall, and (3) a nearly 180-degree turn in the trailing edge. In addition, the passage has an irregular cross-section and varies throughout its entire length. A series of heat transfer tests have been performed at Re = 17,000 ∼ 61,000, compared to this tests which uses a new approach, so-called the hybrid liquid crystal technique. The magnitude of local heat transfer coefficient rises sharply in three regions. The first maximum occurs in the region subjected to direct jet impingement as the flow turns into the channel. Compounded with the inlet effect, this maximum, in fact, is the highest heat transfer coefficient over the entire passage. The second and third peaks, both are comparable in magnitude, locate near the trailing edge of the airfoil where the flow experiences a 180-degree turn and near the passage exit with a 90-degree turn. The average value of heat transfer coefficient over the entire passage is about 1.9∼ 2.5 times higher than that with fully developed turbulent flow in a straight channel. This level of enhancement is comparable to that of the conventional ribturbulators with a 90-degree angle-of-attack.

scholarly journals Heat Transfer Measurements to a Gas Turbine Cooling Passage With Inclined Ribs

1996 ◽  
Author(s):  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler ◽  
J. W. Chew
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Scale Model ◽  
Turbine Cooling ◽  
Gas Turbine Cooling ◽  
Cooling Passage

The local heat transfer coefficient distribution over all four walls of a large scale model of a gas turbine cooling passage have been measured in great detail. A new method of determining the heat transfer coefficient to the rib surface has been developed and the contribution of the rib, at 5% blockage, to the overall roughened heat transfer coefficient was found to be considerable. The vortex dominated flow field was interpreted from the detailed form of the measured local heat transfer contours. Computational Fluid Dynamics calculations support this model of the flow and yield friction factors which agree with measured values. Advances in the heat transfer measuring technique and data analysis procedure which confirm the accuracy of the transient method are described in full.

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