An Experimental Investigation of Heat Transfer in an Orthogonally Rotating Channel Roughened With 45 deg Criss-Cross Ribs on Two Opposite Walls

1991 ◽  
Vol 113 (3) ◽  
pp. 346-353 ◽  
Author(s):  
M. E. Taslim ◽  
L. A. Bondi ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Rotation Number ◽  
Turbine Blades ◽  
Steady Increase ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios

Turbine blade cooling is imperative in advanced aircraft engines. The extremely hot gases that operate within the turbine section require turbine blades to be cooled by a complex cooling circuit. This cooling arrangement increases engine efficiency and ensures blade materials a longer creep life. One principle aspect of the circuit involves serpentine internal cooling passes throughout the core of the blade. Roughening the inside surfaces of these cooling passages with turbulence promoters provides enhanced heat transfer rates from the surface. The purpose of this investigation was to study the effect of rotation, aspect ratio, and turbulator roughness on heat transfer in these rib-roughened passages. The investigation was performed in an orthogonally rotating setup to simulate the actual rotation of the cooling passages. Single-pass channels, roughened on two opposite walls, with turbulators positioned at 45 deg angle to the flow, in a criss-cross arrangement, were studied throughout this experiment. The ribs were arranged such that their pitch-to-height ratio remained at a constant value of 10. An aspect ratio of unity was investigated under three different rib blockage ratios (turbulator height/channel hydraulic diameter) of 0.1333, 0.25, and 0.3333. A channel with an aspect ratio of 2 was also investigated for a blockage ratio of 0.25. Air was flown radially outward over a Reynolds number range of 15,000 to 50,000. The rotation number was varied from 0 to 0.3. Stationary and rotating cases of identical geometries were compared. Results indicated that rotational effects are more pronounced in turbulated passages of high aspect and low blockage ratios for which a steady increase in heat transfer coefficient is observed on the trailing side as rotation number increases while the heat transfer coefficient on the leading side shows a steady decrease with rotation number. However, the all-smooth-wall classical pattern of heat transfer coefficient variation on the leading and trailing sides is not followed for smaller aspect ratios and high blockage ratios when the relative artificial roughness is high.

scholarly journals An Experimental Investigation of Heat Transfer in an Orthogonally Rotating Channel Roughened With 45 Degree Criss-Cross Ribs on Two Opposite Walls

1990 ◽  
Author(s):  
M. E. Taslim ◽  
L. A. Bondi ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Rotation Number ◽  
Turbine Blades ◽  
Steady Increase ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios

Turbine blade cooling is imperative in advanced aircraft engines. The extremely hot gases that operate within the turbine section require turbine blades to be cooled by a complex cooling circuit. This cooling arrangement increases engine efficiency and ensures blade materials a longer creep life. One principle aspect of the circuit involves serpentine internal cooling passes throughout the core of the blade. Roughening the inside surfaces of these cooling passages with turbulence promoters provides enhanced heat transfer rates from the surface. The purpose of this investigation was to study the effects of rotation, aspect ratio, and turbulator roughness on heat transfer in these rib-roughened passage. The investigation was performed in an orthogonally rotating setup to simulate the actual rotation of the cooling passages. Single pass channels, roughened on two opposite walls, with turbulators positioned at a 45° angle to the flow, in a criss-cross arrangement, were studied throughout this experiment. The ribs were arranged such that their pitch-to-height ratio remained at a constant value of 10. An aspect ratio of unity was investigated under three different rib blockage ratios (turbulator height/channel hydraulic diameter) of 0.1333, 0.25, and 0.3333. A channel with an aspect ratio of 2 was also investigated for a blockage ratio of 0.25. Air was flown radially outward over a Reynolds number range of 15000 to 50000. Rotation number was varied from 0 to 0.3. Stationary and rotating cases of identical geometries were compared. Results indicate that rotational effects are more pronounced in turbulated passages of high aspect and low blockage ratios for which a steady increase in heat transfer coefficient is observed on the trailing side as rotation number increases while the heat transfer coefficient on the leading side shows a steady decrease with rotation number. However, the all-smooth-wall classical pattern of heat transfer coefficient variation on the leading and trailing sides is not followed for smaller aspect ratios and high blockage ratios when the relative artificial roughness is high.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Low-Aspect-Ratio Rib Heat Transfer Coefficient Measurements in a Square Channel

1998 ◽  
Vol 120 (4) ◽  
pp. 831-838 ◽  
Author(s):  
M. E. Taslim ◽  
G. J. Korotky
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Turbine Blades ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Low Aspect Ratio ◽  
The Heat Transfer Coefficient

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of round-corner, low-aspect-ratio (ARrib = 0.667) ribs. Twelve rib geometries, comprising three rib height-to-channel hydraulic diameters (blockage ratios) of 0.133, 0.167, and 0.25 as well as three rib spacings (pitch-to-height ratios) of 5, 8.5, and 10 were investigated for two distinct thermal boundary conditions of heated and unheated channel walls. A square channel, roughened with low-aspect-ratio ribs on two opposite walls in a staggered manner and perpendicular to the flow direction, was tested. An instrumented copper rib was positioned either in the middle of the rib arrangements or in the furthest upstream location. Both rib heat transfer coefficient and channel friction factor for these low-aspect-ratio ribs were also compared with those of square ribs, reported previously by the authors. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared.

Experiment study on condensation heat transfer and pressure drop of steam flow inside rectangular tube with different aspect ratio

2020 ◽  
pp. 095765092097222
Author(s):  
Yan Yan ◽  
Jixian Dong ◽  
Tong Ren ◽  
Shiyu Feng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Aspect Ratios ◽  
Rectangular Tubes ◽  
Condensation Heat Transfer Coefficient

In this study, the condensation heat transfer coefficient and pressure drop of steam are obtained in small rectangular tubes with different aspect ratios. The experiments were carried out on three rectangular tubes with aspect ratios of 1:2, 1:3 and 1:5, with mass flux between 25 and 45 kg/m2s, and vapor qualities between 0.1 and 0.8. The experimental data were analyzed to determine the effect of vapor quality, mass flux, and aspect ratio on the heat transfer coefficient and pressure drop. The results showed that the effect of aspect ratio on condensation heat transfer coefficient appears to be dependent on the flow pattern. For stratified flow, the condensation heat transfer coefficient increases as the mass flux increases. For annular flow, the condensation heat transfer coefficient hardly changed. The pressure drop always increases as the aspect ratio increases. Previous studies on round tube heat transfer and pressure drop correlations have not successfully predicted the small rectangular tube data; therefore, modified Shah correlation and Lockhart & Martinelli correlation are proposed, which predict the data with 20% and 23% RMS error, respectively.

scholarly journals Experimental Study of the Effects of Bleed Holes on Heat Transfer and Pressure Drop in Trapezoidal Passages With Tapered Turbulators

1993 ◽  
Author(s):  
M. E. Taslim ◽  
T. Li ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Continuous Change ◽  
Trailing Edge ◽  
Aspect Ratios ◽  
Mainstream Flow ◽  
Cooling Passage ◽  
Cooling Air

Trailing edge cooling cavities in modern gas turbine blades often have trapezoidal cross-sectional areas of relatively low aspect ratio. To enhance cooling effectiveness in these passages, they are roughened with tapered turbulators. Furthermore, to provide additional cooling for the trailing edge, the cooling air may be ejected through trailing edge slots as it moves radially along the cooling passage. The tapered turbulators, in conjunction with the presence of these slots along the smaller base of the trapezoidal cavity, create spanwise as well as longitudinal variations in heat transfer coefficient on the turbulated walls. Moreover, the continuous variation of cooling air velocity along these passages causes a continuous change in static pressure which also requires investigation. Liquid crystals are used in this experimental investigation to study the effects of tapered turbulators on heat transfer coefficients in trailing edge passages with and without bleed holes. The tapered turbulators are configured on two opposite walls of the trapezoidal test section in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90°. Nine different test geometries consisting of two passage aspect ratios, AR, were tested over a range of turbulator aspect ratios, ARt, blockage ratios, emax/Dh, pitch-to-height ratios, S/emax, and Reynolds numbers. Channel pressure losses were also measured and both heat transfer and friction factor results for several geometries are compared. It is concluded that a) there exists a large spanwise variation in heat transfer coefficient in test sections with no bleed holes, b) adding bleed holes to the smaller base of the trapezoidal cavity gives a spanwise velocity component to the mainstream flow and reduces this variation, and c) Nusselt numbers measured in the test sections with bleed holes correlate well with local Reynolds number.

Developing Buoyancy-Modified Turbulent Flow in Ducts Rotating in Orthogonal Mode

1995 ◽  
Vol 117 (3) ◽  
pp. 474-484 ◽  
Author(s):  
T. Bo ◽  
H. Iacovides ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Rotation Number ◽  
Numerical Study ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Wall Region ◽  
Flow Development

A numerical study of developing flow through a heated duct of square cross section rotating in orthogonal mode is reported. The two main aims are to explore the effects of rotational buoyancy on the flow development and to assess the ability of available turbulence models to predict such flows. Two test cases have been computed corresponding to values of the rotation number, Ro, of 0.12 and 0.24, which are typical of operating conditions in internal cooling passages of gas turbine blades. Computations from three turbulence models are presented: a k–ε eddy viscosity (EVM) model matched to a low-Reynolds-number one-equation EVM in the near-wall region; a low-Re k–ε EVM and a low-Re algebraic stress model (ASM). Additional computations in which the fluid density is assumed to remain constant allow the distinct contributions from buoyancy and Coriolis forces to be separated. It is thus shown that rotational buoyancy can have a substantial influence on the flow development and that, in the case of outward flow, it leads to a considerable increase of the side-averaged heat transfer coefficient. The Coriolis-induced secondary motion leads to an augmentation of the mean heat transfer coefficient on the pressure surface and a reduction on the suction side. The k–ε/one-equation EVM produces a mostly reasonable set of heat transfer predictions, but some deficiencies do emerge at the higher rotation number. In contrast, predictions with the low-Re k–ε EVM return a spectacularly unrealistic behavior while the low-Re ASM thermal predictions are in encouragingly close agreement with available measurements.

scholarly journals Low-Aspect-Ratio Rib Heat Transfer Coefficient Measurements in a Square Channel

1997 ◽  
Author(s):  
M. E. Taslim ◽  
G. J. Korotky
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Turbine Blades ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Low Aspect Ratio ◽  
The Heat Transfer Coefficient

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of round-corner, low-aspect-ratio (ARrib = 0.667) ribs. Twelve rib geometries, comprising of three rib height-to-channel hydraulic diameter (blockage ratios) of 0.133, 0.167, and 0.25 as well as three rib spacings (pitch-to-height ratios) of 5, 8.5, and 10 were investigated for two distinct thermal boundary conditions of heated and unheated channel walls. A square channel, roughened with low-aspect-ratio ribs on two opposite walls in a staggered manner end perpendicular to the flow direction was tested. An instrumented copper rib was positioned either in the middle of the rib arrangements or in the furthest upstream location. Rib heat transfer coefficient as well as the channel friction factor for these low-aspect-ratio ribs were also compared with those of square ribs, reported previously by the authors. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared.

Experimental Study of the Effects of Bleed Holes on Heat Transfer and Pressure Drop in Trapezoidal Passages With Tapered Turbulators

1995 ◽  
Vol 117 (2) ◽  
pp. 281-289 ◽  
Author(s):  
M. E. Taslim ◽  
T. Li ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Continuous Change ◽  
Trailing Edge ◽  
Aspect Ratios ◽  
Mainstream Flow ◽  
Cooling Passage ◽  
Cooling Air

Trailing edge cooling cavities in modern gas turbine blades often have trapezoidal cross-sectional areas of relatively low aspect ratio. To enhance cooling effectiveness in these passages, they are roughened with tapered turbulators. Furthermore, to provide additional cooling for the trailing edge, the cooling air may be ejected through trailing edge slots as it moves radially along the cooling passage. The tapered turbulators, in conjunction with the presence of these slots along the smaller base of the trapezoidal cavity, create both spanwise and longitudinal variations in heat transfer coefficient on the turbulated walls. Moreover, the continuous variation of cooling air velocity along these passages causes a continuous change in static pressure, which also requires investigation. Liquid crystals are used in this experimental investigation to study the effects of tapered turbulators on heat transfer coefficients in trailing edge passages with and without bleed holes. The tapered turbulators are configured on two opposite walls of the trapezoidal test section in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90 deg. Nine different test geometries consisting of two passage aspect ratios, AR, were tested over a range of turbulator aspect ratios, ARt, blockage ratios, emax/Dh, pitch-to-height ratios, S/emax, and Reynolds numbers. Channel pressure losses were also measured and both heat transfer and friction factor results for several geometries are compared. It is concluded that (a) there exists a large spanwise variation in heat transfer coefficient in test sections with no bleed holes, (b) adding bleed holes to the smaller base of the trapezoidal cavity gives a spanwise velocity component to the mainstream flow and reduces this variation, and (c) Nusselt numbers measured in the test sections with bleed holes correlate well with local Reynolds number.

Heat Transfer Measurements Using the Hybrid Heat Transfer Technique With Thermally Adiabatic and Participating Ribs

2013 ◽  
Author(s):  
Lucky V. Tran ◽  
Jayanta S. Kapat ◽  
Anne L. Pham ◽  
Zachary D. Little ◽  
Patrick K. Tran
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystals ◽  
Transfer Coefficient ◽  
Hydraulic Diameter ◽  
Bulk Temperature ◽  
Internal Cooling ◽  
Number Range ◽  
Square Channel ◽  
Thermochromic Liquid Crystals

This work is focused on the application of a number of improvements to the traditional transient thermochromic liquid crystals technique, in particular the hybrid heat transfer experiment, in order to provide more detailed and accurate measurements of the surface heat transfer coefficient in internal cooling passages. More accurate measurements of heat transfer coefficient are necessary to provide a clearer understanding of the performance of the cooling channels and to not misrepresent the channel performance so that more optimal designs and progress can be achieved. Detailed Nusselt number measurements were performed for a square channel with ribs on one wall in the Reynolds number range of 50 000 to 150 000, based on channel hydraulic diameter, using the transient thermochromic liquid crystals technique. The rib aspect ratio is 1:1, the rib height-to-hydraulic diameter ratio is 0.10, the rib-pitch–to–rib-height ratio is 10, and the ribs are oriented orthogonal to the streamwise direction. Heat transfer measurements were taken on all four walls so that the bulk temperature variation throughout the channel during the experiment can also be taken into account. Adiabatic and aluminum ribs were used simultaneously. The recently developed Coupled 0D-1D model is used to resolve the average heat transfer of the metallic rib features. A comparison of the data obtained using adiabatic and metallic rib features is made to quantify experimentally the influence of the rib-induced contamination. Friction augmentation, overall heat transfer augmentation, and overall thermal performance are also reported.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45 deg to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100–0.058 for AR 1:1–1:6, respectively. The experiments span a Reynolds number range of 4000–130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

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