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

2003 ◽  
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.

Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 375-385 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]

scholarly journals Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall beat flux boundary condition) using infrared thermography, in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20000. Bulk helical flow is produced in each chamber by two inlets which ore tangent to the swirl chamber circumference. Important changes to local and globally-averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally-averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tiad to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Görtler vnrtex pair trajectories greater skewness as they are advected downstream of each inlet.

Heat Transfer Predictions for U-Shaped Coolant Channels With Skewed Ribs and With Smooth Walls

1996 ◽  
Author(s):  
Bernhard Bonhoff ◽  
Uwe Tomm ◽  
Bruce V. Johnson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Computational Study ◽  
Flow Direction ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Internal Cooling ◽  
Smooth Wall ◽  
Wall Model

A computational study was performed for the flow and heat transfer in coolant passages with two legs connected with a U-bend and with dimensionless flow conditions typical of those in the internal cooling passages of turbine blades. The first model had smooth surfaces on all walls. The second model had opposing ribs staggered and angled at 45° to the main flow direction on two walls of the legs, corresponding to the coolant passage surfaces adjacent to the pressure and suction surfaces of a turbine airfoil. For the ribbed model, the ratio of rib height to duct hydraulic diameter equaled 0.1, and the ratio of rib spacing to rib height equaled 10. Comparisons of calculations with previous measurements are made for a Reynolds number of 25,000. With these conditions, the predicted heat transfer is known to be strongly influenced by the turbulence and wall models. The k-e model, the low Reynolds number RNG k-e and the differential Reynolds-stress model (RSM) were used for the smooth wall model calculation. Based on the results with the smooth walls, the calculations for the ribbed walls were performed using the RSM and k-e turbulence models. The high secondary flow induced by the ribs leads to an increased heat transfer in both legs. However, the heat transfer was nearly unchanged between the smooth wall model and the ribbed model within the bend region. The agreement between the predicted segment-averaged and previously-measured Nusselt numbers was good for both cases.

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sunil Patil ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

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

2008 ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Recirculation Region ◽  
Channel Height ◽  
Internal Cooling ◽  
Height Ratio ◽  
Coriolis Forces ◽  
Heat Transfer Augmentation ◽  
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.

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

2005 ◽  
Vol 127 (4) ◽  
pp. 659-667 ◽  
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.

Heat Transfer in Novel Internally-Finned Heat Exchange Passages

2008 ◽  
Author(s):  
Fuguo Zhou ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Flow Direction ◽  
Turbine Blades ◽  
Internal Heat ◽  
High Heat ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
High Heat Transfer

Heat exchange passages usually use internal fins to enhance heat transfer. These fins have ranged from simple ribs or turbulators to complex helical inserts. Applications of interest range from traditional heat exchangers to internal cooling of turbine blades. In the present paper, a novel fin design that combines the benefits of swirl, impingement and high heat transfer surface area is presented. Measurements of the internal heat transfer coefficients are provided using a liquid crystal technique. Pressure drop along the passage are also measured, therefore friction factors and thermal performance factors are presented. The experiments cover Reynolds number from 10,000 to 40,000 based on the hydraulic diameter of the main channel of the test section. Two models are tested, which have fins oriented at 30 degree and 45 degree to the flow direction, respectively. The results demonstrate that these novel designs produce overall heat transfer ratios greater than 3 compared to the smooth passage.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With 45° Angled Rib Turbulators

2004 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Rotation Effect ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Rotation Numbers ◽  
Rib Turbulators

This paper reports the heat transfer coefficients in two-pass rotating rectangular channels (AR=1:2 and AR=1:4) with rib roughened walls. Rib turbulators are placed on the leading and trailing walls of the two-pass channel at an angle of 45° to the flow direction. Four Reynolds numbers are considered from 5000 to 40000. The rotation numbers vary from 0.0 to 0.3. The ribs have a 1.59 by 1.59 mm square cross section. The rib height-to-hydraulic diameter ratios (e/Dh) are 0.094 and 0.078 for AR=1:2 and AR=1:4, respectively. The rib pitch-to-height ratio (P/e) is 10 for both cases, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115. For each channel, two channel orientation are studied, 90° and 45° with respect to the plane of rotation. The results show that the rotation effect increased the heat transfer on trailing wall in the first pass, but reduced the heat transfer on the leading wall. For AR=1:4, the minimum heat transfer coefficient was 25% of the stationary value. However, the rotation effect reduced the heat transfer difference between the leading and trailing walls in the second pass.

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

2004 ◽  
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.

An LES Insight Into Convective Mechanism of Heat Transfer in a Wall-Bounded Pin Matrix

2010 ◽  
Author(s):  
Giovanni Delibra ◽  
Domenico Borello ◽  
Kemal Hanjalic ◽  
Franco Rispoli
Keyword(s):  
Heat Transfer ◽  
Turbulent Transport ◽  
Turbine Blades ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Internal Cooling ◽  
Gas Turbine Blades ◽  
The Matrix ◽  
Staggered Arrangement ◽  
Set Up

We report on an LES (large-eddy-simulations) study of flow and heat transfer in a longitudinal periodic segment of a matrix of cylindrical rods in a staggered arrangement bounded by two parallel heated walls. The configuration replicates the set-up investigated experimentally by Ames et al. (ASME Turbo Expo, GT2007-27432) and mimics the situation encountered in internal cooling of gas-turbine blades. LES have been performed using the in-house finite-volume computational code T-FlowS. Considered are two Reynolds numbers, 10000 and 30000, based on the rod diameter and maximum velocity in the matrix. The unstructured grid contained around 5 and 15 million cells for the two Re numbers respectively. After validating the simulations with respect to the available experimental data, the paper discusses the characteristic vortex and plume structures, streamline and heatline patterns and their evolution along the pin matrix, around individual pins and at the pin-endwall junctions. It is concluded that the convection by organized vertical structures originated from vortex shedding govern the thermal field and play the key role in endwall heat transfer, exceeding by far the stochastic turbulent transport.

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