Effect of Coriolis Forces in a Rotating Channel With Dimples and Protrusions

Rotation Numbers ◽

Flow Reynolds Number

The use of dimple-protrusions for internal cooling of rotating turbine blades has been investigated. A channel with dimple imprint diameter to channel height ratio (H/D = 1.0), dimple depth to channel height ratio (δ/H = 0.2), spanwise and streamwise pitch to channel height ratios (P/H = S/H = 1.62) was modeled. Four rotation numbers; Rob = 0.0, 0.15, 0.39, and 0.64, at nominal flow Reynolds number, ReH = 10000, were investigated to quantify the effect of Coriolis forces on the flow structure and heat transfer in the channel. Under the influence of rotation, the leading (protrusion) side of the channel showed weaker flow impingement, larger wakes and delayed flow reattachment with increasing rotation number. The trailing (dimple) side experienced a smaller recirculation region inside the dimple and stronger flow ejection from the dimple cavity with increasing rotation. Secondary flow structures in the cross-section played a major role in transporting momentum away from the trailing side at high rotation numbers and limiting heat transfer augmentation. While heat transfer augmentation on the trailing side increases by over 90% at Rob = 0.64, overall Nusselt number and friction coefficient augmentation ratios decrease from 2.5 to 2.05, and 5.74 to 4.78, respectively, as rotation increased from Rob = 0 to Rob = 0.64.

Heat Transfer From Low Aspect Ratio Pin Fins

Volume 4: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27431 ◽

2007 ◽

Cited By ~ 12

Author(s):

Michael E. Lyall ◽

Alan A. Thrift ◽

Atul Kohli ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Aspect Ratio ◽

Gas Turbines ◽

Channel Height ◽

Internal Cooling ◽

Number Range ◽

Pin Fin ◽

Low Aspect Ratio ◽

Pin Fins

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 to 30,000. Both pressure drop and spatially-resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.

Investigation of Coriolis Forces Effect of Flow Structure and Heat Transfer Distribution in a Rotating Dimpled Channel

10.1115/1.4003027 ◽

2011 ◽

Vol 134 (3) ◽

Cited By ~ 5

Author(s):

Mohammad A. Elyyan ◽

Danesh K. Tafti

Keyword(s):

Heat Transfer ◽

Flow Structure ◽

Recirculation Zone ◽

Channel Height ◽

Coriolis Forces ◽

Flow Recirculation ◽

Wide Range ◽

Large Eddy ◽

Dimple Surface

Large-eddy simulations are used to investigate Coriolis forces effect on flow structure and heat transfer in a rotating dimpled channel. Two geometries with two dimple depths are considered, δ=0.2 and 0.3 of channel height, for a wide range of rotation number, Rob=0.0–0.70, based on mean bulk velocity and channel height. It is found that the turbulent flow is destabilized near the trailing side and stabilized near the leading side, with secondary flow structures generated in the channel under the effect of Coriolis forces. Higher heat transfer levels are obtained at the trailing surface of the channel, especially in regions of flow reattachment and boundary layer regeneration at the dimple surface. Coriolis forces showed a stronger effect on the flow structure for the shallow dimple geometry (δ=0.2) compared with the deeper dimple where the growth and shrinkage of the flow recirculation zone in the dimple cavity with rotation were more pronounced than the deep dimple geometry (δ=0.3). Under the action of rotation, heat transfer augmentation increased by 57% for δ=0.2 and by 70% for δ=0.3 on the trailing side and dropped by 50% for δ=0.2 and by 45% for δ=0.3 on the leading side from that of the stationary case.

Investigation of Coriolis Forces Effect of Flow Structure and Heat Transfer Distribution in a Rotating Dimpled Channel

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-22657 ◽

2010 ◽

Cited By ~ 3

Author(s):

Mohammad A. Elyyan ◽

Danesh K. Tafti

Keyword(s):

Heat Transfer ◽

Flow Structure ◽

Recirculation Zone ◽

Channel Height ◽

Coriolis Forces ◽

Flow Recirculation ◽

Wide Range ◽

Large Eddy ◽

Dimple Surface

Large-eddy simulations are used to investigate Coriolis forces effect on flow structure and heat transfer in a rotating dimpled channel. Two geometries with two dimple depths are considered, δ = 0.2 and 0.3 of channel height, for a wide range of rotation number, Rob = 0.0–0.70, based on mean bulk velocity and channel height. It is found that the turbulent flow is destabilized near the trailing side and stabilized near the leading side, with secondary flow structures generated in the channel under the effect of Coriolis forces. Higher heat transfer levels are obtained at the trailing surface of the channel, especially in regions of flow reattachment and boundary layer regeneration at the dimple surface. Coriolis forces showed a stronger effect on the flow structure for the shallow dimple geometry (δ = 0.2) compared to the deeper dimple where the growth and shrinkage of the flow recirculation zone in the dimple cavity with rotation were more pronounced than the deep dimple geometry (δ = 0.3). Under the action of rotation, heat transfer augmentation increased by 57% for δ = 0.2 and by 70% for δ = 0.3 on the trailing side and dropped by 50% for δ = 0.2 and by 45% for δ = 0.3 on the leading side from that of the stationary case.

Oscillator Fin as a Novel Heat Transfer Augmentation Device for Gas Turbine Cooling Applications

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/98-gt-150 ◽

1998 ◽

Cited By ~ 2

Author(s):

Oguz Uzol ◽

Cengiz Camci

Keyword(s):

Heat Transfer ◽

Kinetic Energy ◽

Gas Turbine ◽

Turbulent Kinetic Energy ◽

Stokes Equations ◽

Turbine Blades ◽

Local Heat Transfer ◽

Internal Cooling ◽

Pin Fin ◽

Heat Transfer Augmentation

A new concept for enhanced turbulent transport of heat in internal coolant passages of gas turbine blades is introduced. The new heat transfer augmentation component called “oscillator fin” is based on an unsteady flow system using the interaction of multiple unsteady jets and wakes generated downstream of a fluidic oscillator. Incompressible, unsteady and two dimensional solutions of Reynolds Averaged Navier-Stokes equations are obtained both for an oscillator fin and for an equivalent cylindrical pin fin and the results are compared. Preliminary results show that a significant increase in the turbulent kinetic energy level occur in the wake region of the oscillator fin with respect to the cylinder with similar level of aerodynamic penalty. The new concept does not require additional components or power to sustain its oscillations and its manufacturing is as easy as a conventional pin fin. The present study makes use of an unsteady numerical simulation of mass, momentum, turbulent kinetic energy and dissipation rate conservation equations for flow visualization downstream of the new oscillator fin and an equivalent cylinder. Relative enhancements of turbulent kinetic energy and comparisons of the total pressure field from transient simulations qualitatively suggest that the oscillator fin has excellent potential in enhancing local heat transfer in internal cooling passages without significant aerodynamic penalty.

The Effect of Turning Vanes on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel

10.1115/1.4000550 ◽

2010 ◽

Vol 133 (2) ◽

Cited By ~ 22

Author(s):

Marco Schüler ◽

Frank Zehnder ◽

Bernhard Weigand ◽

Jens von Wolfersdorf ◽

Sven Olaf Neumann

Keyword(s):

Heat Transfer ◽

Pressure Loss ◽

Stokes Equations ◽

Turbine Blades ◽

Local Heat Transfer ◽

Width Ratio ◽

Channel Height ◽

Internal Cooling ◽

Thermochromic Liquid Crystal ◽

Sharp Turn

Gas turbine blades are usually cooled by using ribbed serpentine internal cooling passages, which are fed by extracted compressor air. The individual straight ducts are connected by sharp 180 deg bends. The integration of turning vanes in the bend region lets one expect a significant reduction in pressure loss while keeping the heat transfer levels high. Therefore, the objective of the present study was to investigate the influence of different turning vane configurations on pressure loss and local heat transfer distribution. The investigations were conducted in a rectangular two-pass channel connected by a 180 deg sharp turn with a channel height-to-width ratio of H/W=2. The channel was equipped with 45 deg skewed ribs in a parallel arrangement with e/dh=0.1 and P/e=10. The tip-to-web distance was kept constant at Wel/W=1. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Furthermore static pressure measurements were conducted in order to determine the influence of turning vane configurations on pressure loss. Additionally, the configurations were investigated numerically by solving the Reynolds-averaged Navier–Stokes equations using the finite-volume solver FLUENT. The numerical grids were generated by the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f turbulence model. The results showed a significant influence of the turning vane configuration on pressure loss and heat transfer in the bend region and the outlet pass. While using an appropriate turning vane configuration, pressure loss was reduced by about 25%, keeping the heat transfer at nearly the same level in the bend region. An inappropriate configuration led to an increase in pressure loss while the heat transfer was reduced in the bend region and outlet pass.

Fluid Flow and Heat Transfer in Rotating Curved Duct at High Rotation and Density Ratios

10.1115/1.2019276 ◽

2005 ◽

Vol 127 (4) ◽

pp. 659-667 ◽

Cited By ~ 13

Author(s):

A. K. Sleiti ◽

J. S. Kapat

Keyword(s):

Heat Transfer ◽

Turbine Blades ◽

Density Ratio ◽

Reynolds Stress Model ◽

Wall Region ◽

Internal Cooling ◽

Cooling Channels ◽

Rotation Numbers ◽

Effects Of Rotation ◽

Density Ratios

Prediction of flow field and heat transfer of high rotation numbers and density ratio flow in a square internal cooling channels of turbine blades with U-turn as tested by Wagner et al. (ASME J. Turbomach., 113, pp. 42–51, 1991) is the main focus of this study. Rotation, buoyancy, and strong curvature affect the flow within these channels. Due to the fact that RSM turbulence model can respond to the effects of rotation, streamline curvature and anisotropy without the need for explicit modeling, it is employed for this study as it showed improved prediction compared to isotropic two-equation models. The near wall region was modeled using enhanced wall treatment approach. The Reynolds Stress Model (RSM) was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention is given to how secondary flow, velocity and temperature profiles, turbulence intensity, and Nusselt number area affected by Coriolis and buoyancy/centrifugal forces caused by high levels of rotation and buoyancy in the immediate vicinity of the bend. The results showed that four-side-average Nu, similar to low Ro cases, increases linearly by increasing rotation number and, unlike low Ro cases, decreases slightly by increasing density ratio.

Study of Flow Structures and Heat Transfer in Parallel Fins With Dimples and Protrusions Using Large Eddy Simulation

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2006-98113 ◽

2006 ◽

Cited By ~ 3

Author(s):

M. Elyyan ◽

A. Rozati ◽

D. K. Tafti

Keyword(s):

Heat Transfer ◽

Turbulent Energy ◽

Channel Height ◽

Height Ratio ◽

Pressure Drag ◽

Eddy Simulation ◽

Flow And Heat Transfer ◽

Separated Shear Layer ◽

Large Eddy

Flow field and heat transfer for parallel fins with dimples and protrusions are predicted with large-eddy simulations at a nominal Reynolds number based on fin pitch of 15,000. Dimple and protrusion depth and imprint diameter to channel height ratio are 0.4 and 2.0, respectively. The results show that on the dimple side, the flow and heat transfer is dominated by unsteady vorticity generated and ejected out by the separated shear layer in the dimple. The high turbulent energy which results from the unsteady dynamics is mostly responsible for heat transfer augmentation on the dimple side. A maximum augmentation of about 4 occurs in the reattachment zone of the dimple and immediately downstream of it. On the protrusion side, however, the augmentation in heat transfer is dominated by flow impingement at the front of the protrusion, which results in a maximum augmentation of 5.2. The overall heat transfer and friction coefficient augmentations of 2.34 and 6.35 are calculated for this configuration. Pressure drag from the dimple cavity and protrusion contribute 82% of the total pressure drop.

Heat Transfer and Flow Field Measurements in a Rib-Roughened Branch of a Rotating Two-Pass Duct

Volume 5: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38048 ◽

2003 ◽

Cited By ~ 5

Author(s):

Yves Servouze ◽

J. Chris Sturgis

Keyword(s):

Heat Transfer ◽

Flow Direction ◽

Turbine Blades ◽

Field Measurements ◽

Reynolds Numbers ◽

Experimental Program ◽

Internal Cooling ◽

Nusselt Numbers ◽

Critical Technology ◽

Rotation Numbers

Internal cooling of gas engine turbine blades is a critical technology. This paper addresses the subject by presenting the results of an experimental program that uses a rotating, square-cross-section, U-shaped channel to model the blade coolant passage. The channel is heated, instrumented and furnished with angled ribs (60° to flow direction) on two walls of one branch. Air is the coolant. Internal Nusselt numbers are calculated on the four walls at various locations along the flow in both the centrifugal and centripetal branches for two Reynolds numbers (5000, 25000) and several Rotation numbers (0.033, 0.066, 0.1, 0.33). Data indicate greater heat transfer on the trailing wall than leading wall in the centrifugal branch; likewise, for the upper wall compared to the lower wall. Centripetal branch heat transfer is affected by bend effects. Particle Image Velocimetry measurements in both the stationary and rotating channels reveal the presence of vortices. The large number of measurements is useful for comparison with numerical calculations.

Fluid Flow and Heat Transfer in Rotating Curved Duct at High Rotation and Density Ratios

Volume 3: Turbo Expo 2004 ◽

10.1115/gt2004-53028 ◽

2004 ◽

Cited By ~ 1

Author(s):

A. K. Sleiti ◽

J. S. Kapat

Keyword(s):

Heat Transfer ◽

Turbine Blades ◽

Density Ratio ◽

Wall Region ◽

Internal Cooling ◽

Cooling Channels ◽

Streamline Curvature ◽

Rotation Numbers ◽

Effects Of Rotation ◽

Density Ratios

Prediction of flow field and heat transfer of high rotation numbers and density ratio flow in a square internal cooling channels of turbine blades with U-turn as tested by Wagner et. al (1991) is the main focus of this study. Rotation, buoyancy and strong curvature affect the flow within these channels. Due to the fact that RSM turbulence model can respond to the effects of rotation, streamline curvature and anisotropy without the need for explicit modeling, it is employed for this study as it showed improved prediction compared to isotropic two-equation models. The near wall region was modeled using enhanced wall treatment approach. RSM was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention is given to how secondary flow, velocity and temperature profiles, turbulence intensity and Nusselt number area affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and buoyancy in the immediate vicinity of the bend. The results showed that 4-side-average Nu, similar to low Ro cases, increases linearly by increasing rotation number and, unlike low Ro cases, decreases slightly by increasing density ratio.

Heat Transfer From Low Aspect Ratio Pin Fins

10.1115/1.2812951 ◽

2010 ◽

Vol 133 (1) ◽

Cited By ~ 25

Author(s):

Michael E. Lyall ◽

Alan A. Thrift ◽

Karen A. Thole ◽

Atul Kohli

Keyword(s):

Heat Transfer ◽

Aspect Ratio ◽

Gas Turbines ◽

Channel Height ◽

Internal Cooling ◽

Number Range ◽

Pin Fin ◽

Low Aspect Ratio ◽

Pin Fins

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 and 30,000. Both pressure drop and spatially resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.