Prediction of Flow and Heat Transfer in Rotating Two-Pass Rectangular Channels With 45-deg Rib Turbulators

2002 ◽  
Vol 124 (2) ◽  
pp. 242-250 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Convective Transport ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Rectangular Channels ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Numerical predictions of three-dimensional flow and heat transfer are presented for a rotating two-pass rectangular channel with 45-deg rib turbulators and channel aspect ratio of 2:1. The rib height-to-hydraulic diameter ratio e/Dh is 0.094 and the rib-pitch-to-height ratio P/e is 10. Two channel orientations are studied: β=90deg and 135 deg, corresponding to the mid-portion and the trailing edge regions of a turbine blade, respectively. The focus of this study is twofold; namely, to investigate the effect of the channel aspect ratio and the channel orientation on the nature of the flow and heat transfer enhancement. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. The numerical results compare reasonably well with experimental data for both stationary and rotating rectangular channels with rib turbulators at Reynolds number (Re) of 10,000, rotation number (Ro) of 0.11 and inlet coolant-to-wall density ratio (Δρ/ρ) of 0.115.

Prediction of Flow and Heat Transfer in Rotating Two-Pass Rectangular Channels With 45° Rib Turbulators

2001 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Convective Transport ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Rectangular Channels ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Numerical predictions of three-dimensional flow and heat transfer are presented for a rotating two-pass rectangular channel with 45° rib turbulators and channel aspect ratio of 2:1. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.094 and the rib-pitch-to-height ratio (P/e) is 10. Two channel orientations are studied: β = 90° and β = 135° corresponding to the mid-portion and the trailing edge regions of a turbine blade, respectively. The focus of this study is twofold; namely, to investigate the effect of the channel aspect ratio and the channel orientation on the nature of the flow and heat transfer enhancement. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. The numerical results compare reasonably well with experimental data for both stationary and rotating rectangular channels with rib turbulators at Reynolds number (Re) of 10,000, rotation number (Ro) of 0.11 and inlet coolant-to-wall density ratio (Δρ/ρ) of 0.115.

Computation of Flow and Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:1, AR=1:2, AR=1:4) With 45-deg. Angled Ribs by Reynolds Stress Turbulence Model

2004 ◽  
Author(s):  
Guoguang Su ◽  
Hamn-Ching Chen ◽  
Je-Chin Han ◽  
James D. Heidmann
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Mean Velocity ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Numerical Predictions ◽  
Rib Turbulators

Numerical predictions of three-dimensional flow and heat transfer are presented for rotating two-pass rectangular channel with 45-deg rib turbulators. Three channels with different aspect ratios (AR=1:1; AR=1:2; AR=1:4) were investigated. Detailed predictions of mean velocity, mean temperature, and Nusselt number for two Reynolds numbers (Re = 10,000 and Re = 100,000) were carried out. The rib height is fixed as constant and the rib-pitch-to-height ratio (P/e) is 10, but the rib height-to-hydraulic diameter ratios (e/Dh) are 0.125, 0.094, and 0.078, for AR=1:1, AR=1:2, and AR=1:4 channel, respectively. The channel orientations are set at 90 deg, corresponding to the cooling passages between mid-portion and the leading edge of a turbine blade. The rotation number varies from 0.0 to 0.28 and the inlet coolant-to-wall density ratio varies from 0.13 to 0.40, respectively. The primary focus of this study is the effect of the channel aspect ratio on the nature of the flow and heat transfer enhancement in a rectangular ribbed channel under rotating conditions. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure to provide detailed resolution of the Reynolds stresses and turbulent heat fluxes induced by the rib turbulators under both the stationary and rotating conditions.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2) With Five Different Orientations of 45 Deg V-Shaped Rib Turbulators

2003 ◽  
Vol 125 (2) ◽  
pp. 232-242 ◽  
Author(s):  
Luai AL-Hadhrami ◽  
Todd Griffith ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Height Ratio ◽  
Heat Transfer Augmentation ◽  
Rectangular Channels ◽  
First Pass ◽  
Rib Turbulators ◽  
Channel Aspect Ratio ◽  
Channel Orientation

An experimental study was made to obtain heat transfer data for a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 deg and 135 deg with respect to the plane of rotation). The V-shaped ribs are placed on the leading and trailing surfaces. Five different arrangements of 45 deg V-shaped ribs are studied. The Reynolds number and rotation number ranges are 5000–40000, and 0.0–0.21, respectively. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10; and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115 for every test. The results show that the rotation-induced secondary flow enhances the heat transfer of the first pass trailing surface and second pass leading surface. However, the first pass leading and the second pass trailing surfaces show a decrease in heat transfer with rotation. The results also show that parallel 45 deg V-shaped rib arrangements produce better heat transfer augmentation than inverted 45 deg V-shaped ribs and crossed 45 deg V-shaped ribs, and a 90 deg channel orientation produces greater rotating effect on heat transfer than a 135 deg orientation.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2:1) With Discrete V-Shaped and Discrete Angled Rib Turbulators

2004 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Rotating Speed ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Internally Cooled ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

This paper reports the heat transfer coefficients in a two-pass rotating, rectangular channel with ribs, applicable to an internally cooled turbine blade. The channel aspect ratio is 2:1. Five different turbulators are studied: 45° angled ribs, V-shaped ribs, discrete 45° angled ribs, discrete V-shaped ribs, and crossed V-shaped ribs. The ribs are placed on the leading and trailing surfaces. The Reynolds numbers range from 5000 to 40000. The corresponding rotation numbers vary from 0.21 to 0.026 for a fixed rotating speed of 550 rpm. The rib height-to-hydraulic diameter ratio (e/D) is 0.094, the rib pitch-to-height ratio (P/e) is 10, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115. For each case, two channel orientations are studied, 90° and 135° with respect to the plane of rotation. The results show the V-shaped ribs and discrete V-shaped ribs have higher heat transfer enhancement than the 45° angled ribs and discrete 45° angled ribs for both rotating and non-rotating cases.

A Numerical Study of Flow and Heat Transfer in Rotating Rectangular Channels AR=4 With 45 deg Rib Turbulators by Reynolds Stress Turbulence Model

2003 ◽  
Vol 125 (1) ◽  
pp. 19-26 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Density Ratio ◽  
Convective Transport ◽  
High Density ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Rectangular Channels ◽  
Density Ratios

Computations were performed to study three-dimensional turbulent flow and heat transfer in stationary and rotating 45 deg ribbed rectangular channels for which experimental heat transfer data were available. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio e/Dh is 0.078 and the rib-pitch-to-height ratio P/e is 10. The rotation number and inlet coolant-to-wall density ratios, Δρ/ρ, were varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number was fixed at 10,000. Also, two channel orientations (β=90deg and 135 deg from the rotation direction) were investigated with focus on the high rotation and high density ratios effects on the heat transfer characteristics of the 135 deg orientation. These results show that, for high rotation and high density ratio, the rotation induced secondary flow overpowered the rib induced secondary flow and thus change significantly the heat transfer characteristics compared to the low rotation low density ratio case. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method.

Effect of Rotation on Heat Transfer in Narrow Rectangular Cooling Channels (AR = 8:1 and 4:1) With Pin-Fins

2003 ◽  
Author(s):  
Lesley M. Wright ◽  
Eungsuk Lee ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Pin Fin ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Pin Fins

The effect of rotation on smooth narrow rectangular channels and narrow rectangular channels with pin-fins is investigated in this study. Pin-fins are commonly used in the narrow sections within the trailing edge of the turbine blade; the pin-fins act as turbulators to enhance internal cooling while providing structural support in this narrow section of the blade. The rectangular channel is oriented at 150° with respect to the plane of rotation, and the focus of the study involves narrow channels with aspect ratios of 4:1 and 8:1. The enhancement due to both conducting (copper) pin-fins and non-conducting (plexi-glass) pins is investigated. Due to the varying aspect ratio of the channel, the height-to-diameter ratio (hp/Dp) of the pins varies from two, for an aspect ratio of 4:1, to unity, for an aspect ratio of 8:1. A staggered array of pins with uniform streamwise and spanwise spacing (xp/Dp = sp/Dp = 2.0) is studied. With this array, 42 pin-fins are used, giving a projected surface density of 3.5 pins/in2 (0.543 pins/cm2), for the leading or trailing surfaces. The range of flow parameters include Reynolds number (ReDh = 5000–20000), rotation number (Ro = 0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Heat transfer in a stationary pin-fin channel can be enhanced up to 3.8 times that of a smooth channel. Rotation enhances the heat transferred from the pin-fin channels 1.5 times that of the stationary pin-fin channels. Overall, rotation enhances the heat transfer from all surfaces in both the smooth and pin-fin channels. Finally, as the rotation number increases, spanwise variation increases in all channels.

Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45-deg Angled Rib Turbulators

2002 ◽  
Vol 124 (2) ◽  
pp. 251-259 ◽  
Author(s):  
Gm S. Azad ◽  
Mohammad J. Uddin ◽  
Je-Chin Han ◽  
Hee-Koo Moon ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Main Stream ◽  
Transfer Coefficients ◽  
Experimental Heat ◽  
First Pass ◽  
Result Show ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 and 135 deg to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45 deg to the main stream flow. Both 45-deg parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10,000, and 25,000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10 and the inlet wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45-deg parallel ribs produce a better heat transfer augmentation than 45-deg cross ribs, and a 90-deg channel orientation produces higher heat transfer effect over a 135-deg orientation.

Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45° Angled Rib Turbulators

2001 ◽  
Author(s):  
Gm. S. Azad ◽  
Mohammad J. Uddin ◽  
Je-Chin Han ◽  
Hee-Koo Moon ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Main Stream ◽  
Transfer Coefficients ◽  
Experimental Heat ◽  
First Pass ◽  
Result Show ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90° and 135° to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45° to the main stream flow. Both 45° parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10000, and 25000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10 and the inlet wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45° parallel ribs produce a better heat transfer augmentation than 45° cross ribs, and a 90° channel orientation produces higher heat transfer effect over a 135° orientation.

A Numerical Study of Flow and Heat Transfer in Rotating Rectangular Channels (AR=4) With 45° Rib Turbulators by Reynolds Stress Turbulence Model

2002 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Density Ratio ◽  
Convective Transport ◽  
High Density ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Rectangular Channels ◽  
Density Ratios

Computations were performed to study three-dimensional turbulent flow and heat transfer in a rotating smooth and 45° ribbed rectangular channels for which heat transfer data were available. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio (e/Dh) is 0.078 and the rib-pitch-to-height ratio (P/e) is 10. The rotation number and inlet coolant-to-wall density ratios, Δρ/ρ, were varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number was fixed at 10,000. Also, two channel orientations (β − 90° and 135° from the rotation direction) were investigated with focus on the high rotation and high density ratios effects on the heat transfer characteristics of the 135° orientation. These results show that, for high rotation and high density ratio, the rotation induced secondary flow overpowered the rib induced secondary flow and thus change significantly the heat transfer characteristics compared to the low rotation low density ratio case. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method.

Large Eddy Simulation of Flow and Heat Transfer in a Rectangular Channel With Crossed Angled Ribs

2004 ◽  
Author(s):  
Toshihiko Takahashi ◽  
Kazunori Watanabe
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Large Eddy Simulation ◽  
Rectangular Channel ◽  
Hydraulic Diameter ◽  
Channel Cross Section ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Rectangular Channels ◽  
Large Eddy

Characteristics of fully developed flow and heat transfer in stationary rectangular channels with two opposite ribbed walls, adopted for internal cooling of a gas turbine blade, were investigated by using Large Eddy Simulation (LES). Effect of aspect ratio of the channel cross section on the flow and thermal fields in the channels with crossed, 60-deg. angle ribs was studied. The thermo-flow field in the stationary rectangular channels with the crossed angled ribs has a single secondary swirl in the cross sections, which exhibits a basic pattern for convection in the channels with the angled ribs. The aspect ratio was varied from 0.5 to 2.0. The rib height-to-hydraulic diameter and the rib pitch-to-height ratio were kept at 0.075 and 11.547, respectively. Calculations were conducted for Reynolds number based on the hydraulic diameter at around 50,000 and 120,000. The present calculations showed that formation of rib induced separation vortex varies with the channel aspect ratio. The change in the vortex formation has an influence on augmentation of friction and heat transfer. Current correlations for friction and heat transfer agreed reasonably with previous experiments.

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