Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR = 4) With V-Shaped Ribs by a Reynolds Stress Turbulence Model

2003 ◽  
Author(s):  
Guoguang Su ◽  
Shuye Teng ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Heat Fluxes ◽  
Reynolds Stresses ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Flow And Heat Transfer

Computations were performed to study three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with 45° V-shaped ribs. 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. A total of eight calculations have been performed with various combinations of rotation number, Reynolds number, coolant-to-wall density ratio, and channel orientation. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number varied from 10,000 to 500,000. Three channel orientations (90°, −135°, and 135° from the rotation direction) were also investigated. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, turbulent Reynolds stresses, and heat fluxes and heat transfer coefficients.

Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR=4:1) With Pin-Fins by a Reynolds Stress Turbulence Model

2006 ◽  
Vol 129 (6) ◽  
pp. 685-696 ◽  
Author(s):  
Guoguang Su ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Three Dimensional ◽  
Diameter Ratio ◽  
Mean Velocity ◽  
Flow And Heat Transfer ◽  
Pin Fins

Computations with multi-block chimera grids were performed to study the three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with staggered arrays of pin-fins. The channel aspect ratio (AR) is 4:1, the pin length to diameter ratio (H∕D) is 2.0, and the pin spacing to diameter ratio is 2.0 in both the stream-wise (S1∕D) and span-wise (S2∕D) directions. A total of six calculations have been performed with various combinations of rotation number, Reynolds number, and coolant-to-wall density ratio. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.20, respectively, while the Reynolds number varied from 10,000 to 100,000. For the rotating cases, the rectangular channel was oriented at 150deg with respect to the plane of rotation to be consistent with the configuration of the gas turbine blade. A Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, and heat transfer coefficient distributions.

Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR=4:1) With Pin-Fins by a Reynolds Stress Turbulence Model

2005 ◽  
Author(s):  
Guoguang Su ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Three Dimensional ◽  
Diameter Ratio ◽  
Mean Velocity ◽  
Flow And Heat Transfer ◽  
Pin Fins

Computations with multi-block chimera grids were performed to study the three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with staggered arrays of pin-fins. The channel aspect ratio (AR) is 4:1, the pin length to diameter ratio (H/D) is 2.0, and the pin spacing to diameter ratio is 2.0 in both the stream-wise (S1/D) and span-wise (S2/D) directions. A total of six calculations have been performed with various combinations of rotation number, Reynolds number, and coolant-to-wall density ratio. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.20, respectively, while the Reynolds number varied from 10,000 to 100,000. For the rotating cases, the rectangular channel was oriented at 150 deg with respect to the plane of rotation to be consistent with the configuration of the gas turbine blade. A Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, and heat transfer coefficient distributions.

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 Rotating Rectangular Cooling Channels AR=4 With Angled Ribs

2002 ◽  
Vol 124 (4) ◽  
pp. 617-625 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Strong Dependence ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Rib Turbulators

An investigation into determining the effect of rotation on heat transfer in a rib-roughened rectangular channel with aspect ratio of 4:1 is detailed in this paper. A broad range of flow parameters have been selected including Reynolds number (Re=5000–40000), rotation number (Ro=0.04–0.3) and coolant to wall density ratio at the inlet Δρ/ρi=0.122. The rib turbulators, attached to the leading and trailing surface, are oriented at an angle α=45deg to the direction of flow. The effect of channel orientations of β=90 deg and 135 deg with respect to the plane of rotation is also investigated. Results show that the narrow rectangular passage exhibits a much higher heat transfer enhancement for the ribbed surface than the square and 2:1 duct previously investigated. Also, duct orientation significantly affects the leading and side surfaces, yet does not have much affect on the trailing surfaces for both smooth and ribbed surfaces. Furthermore, spanwise heat transfer distributions exist across the leading and trailing surfaces and are accentuated by the use of angled ribs. The smooth and ribbed case trailing surfaces and smooth case side surfaces exhibited a strong dependence on rotation number.

Flow and Heat Transfer Behavior in Transitional Boundary Layers With Streamwise Acceleration

1996 ◽  
Vol 118 (2) ◽  
pp. 314-326 ◽  
Author(s):  
F. J. Keller ◽  
T. Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Temperature Profiles ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Free Stream Turbulence

The effects of streamwise acceleration on a two-dimensional heated boundary layer undergoing natural laminar-turbulent transition were investigated with detailed measurements of momentum and thermal transport phenomena. Tests were conducted over a heated flat wall with zero pressure-gradient and three levels of streamwise acceleration: K ≡ (v/U∞2) (d/U∞/dx) = 0.07, 0.16, and 0.25 × 10−6. Free-stream turbulence intensities were maintained at approximately 0.5 percent for the baseline case and 0.4 percent for the accelerating cases. A miniature three-wire probe was used to measure mean velocity and temperature profiles, Reynolds stresses, and Reynolds heat fluxes. Transition onset and end were inferred from Stanton numbers and skin-friction coefficients. The results indicate that mild acceleration delays transition onset and increases transition length both in terms of distance, x, and Reynolds number based on x. Transition onset and length are relatively insensitive to acceleration in terms of momentum thickness Reynolds number. This is supported by the boundary layer thickness and integral parameters, which indicate that a favorable pressure gradient suppresses boundary layer growth and development in the transition region. Heat transfer rates and temperature profiles in the late-transition and early-turbulent regions lag behind the development of wall shear stress and velocity profiles. This lag increases as K increases, indicating that the evolution of the heat transport is slower than that of the momentum transport. Comparison of the evolution of rms temperature fluctuations to the evolution of Reynolds normal stresses indicates a similar lag in the rms temperature fluctuations.

Flow and Heat Transfer Behavior in Transitional Boundary Layers With Streamwise Acceleration

1994 ◽  
Author(s):  
F. Jeffrey Keller ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Temperature Profiles ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Free Stream Turbulence

The effects of streamwise acceleration on a two-dimensional heated boundary layer undergoing natural laminar-turbulent transition were investigated with detailed measurements of momentum and thermal transport phenomena. Tests were conducted over a heated flat wall with zero pressure-gradient and three levels of streamwise acceleration: K≡νU¯∞2dU¯∞dx= 0.07, 0.16, and 0.25 × 10−6. Free-stream turbulence intensities were maintained at approximately 0.5% for the baseline case and 0.4% for the accelerating cases. A miniature three-wire probe was used to measure mean velocity and temperature profiles, Reynolds stresses, and Reynolds heat fluxes. Transition onset and end were inferred from Stanton numbers and skin-friction coefficients. The results indicate that mild acceleration delays transition onset and increases transition length both in terms of distance, x1 and Reynolds number based on x. Transition onset and length are relatively insensitive to acceleration in terms of momentum thickness Reynolds number. This is supported by the boundary layer thickness and integral parameters which indicate that a favorable pressure gradient suppresses boundary layer growth and development in the transition region. Heat transfer rates and temperature profiles in the late-transition and early-turbulent regions lag behind the development of wall shear stress and velocity profiles. This lag increases as K increases, indicating that the evolution of the heat transport is slower than that of the momentum transport. Comparison of the evolution of RMS temperature fluctuations to the evolution of Reynolds normal stresses indicates a similar lag in the RMS temperature fluctuations.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring a Converging Tip Turn With Various 45 deg Rib Coverage Designs

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Copper Plate ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
First Passage ◽  
Pressure Loss Coefficient ◽  
Internal Surfaces ◽  
Turbine Airfoils

Varying aspect ratio (AR) channels are found in modern gas turbine airfoils for internal cooling purposes. Corresponding experimental data are needed in understanding and assisting the design of advanced cooling systems. The present study features a two-pass rectangular channel with an AR = 4:1 in the first pass with the radial outward flow and an AR = 2:1 in the second pass with the radial inward flow after a 180 deg tip turn. Effects of rib coverage near the tip region are investigated using profiled 45 deg ribs (P/e = 10, e/Dh ≈ 0.11, parallel and in-line) with three different configurations: less coverage, medium coverage, and full coverage. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage. The highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Heat transfer coefficients on the internal surfaces were obtained by the regionally averaged copper plate method. The results showed that the rotation effects on both heat transfer and pressure loss coefficient are reduced with an increased rib coverage in the tip turn region. Different rib coverage upstream of the tip turn significantly changes the heat transfer in the turn portion. Heat transfer reduction (up to −27%) on the tip wall was seen at lower Ro. Dependence on the Reynolds number can be seen for this particular design. The combined geometric, rib coverage, and rotation effects should be taken into consideration in the internal cooling design.

Unsteady RANS Simulation of Turbulent Flow and Heat Transfer in Ribbed Coolant Passages of Different Aspect Ratios

2004 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Rotation Number ◽  
Large Scale ◽  
Density Ratio ◽  
Navier Stokes ◽  
Flow Structures ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Unsteady Rans

The flow and heat transfer in ribbed coolant passages of aspect ratios (AR) of 1:1, 4:1, and 1:4 are numerically studied through the solution of the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The URANS procedure can resolve large-scale bulk unsteadiness, and utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The computations are carried out for a fixed Reynolds number of 25000 and density ratio of 0.13 while the Rotation number has been varied between 0.12–0.50. The average duct heat transfer is the highest for the 4:1 AR case. For this case, the secondary flow structures consist of multiple roll cells that direct flow both to the trailing and leading surfaces. The 1:4 AR duct shows flow reversal along the leading surface at high rotation numbers with multiple rolls in the secondary flow structures near the leading wall. For this AR, the potential for conduction-limited heat transfer along the leading surface is identified. At high rotation number, both the 1:1 and 4:1 AR cases exhibit loss of axial periodicity over one inter-rib module. The friction factor reveals an increase with the rotation number for all aspect ratio ducts, and shows a sudden jump in its value at a critical rotation number because of either loss of spatial periodicity or the onset of backflow.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

DNS of Expansion Ratio Effects on Three-Dimensional Unsteady Separated Flow and Heat Transfer Around a Downward Step

2005 ◽  
Author(s):  
Aya Kito ◽  
Kazuaki Sugawara ◽  
Hiroyuki Yoshikawa ◽  
Terukazu Ota
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Side Wall ◽  
Separated Flow ◽  
Flow Region ◽  
Expansion Ratio ◽  
Mean Velocity ◽  
Flow And Heat Transfer ◽  
Channel Expansion

The direct numerical simulation methodology was employed to analyze the unsteady features of a three-dimensional separated flow and heat transfer around a downward step in a rectangular channel, and to clarify systematically the channel expansion ratio effects upon them. Numerical calculations were carried out using the finite difference method. The Reynolds number Re based on the mean velocity at inlet and the step height was varied from 300 to 1000. The channel expansion ratio ER is 1.5, 2.0 and 3.0 under a step aspect ratio of 36.0. It is found that the flow is steady upto Re = 500 but becomes sensibly unsteady at Re = 700 for all the three expansion ratios. In the case of ER = 2.0, the separated shear layer is most unstable. In the case of ER = 1.5, the longitudinal vortices formed near the side walls of channel are strongest. Nusselt number reaches its maximum in the reattachment flow region and also in the neighborhood of the side wall, and their locations depend greatly upon ER and Re.

Sign in / Sign up

Export Citation Format

Share Document