Large Eddy Simulation of Flow and Heat Transfer in the 180‐Deg Bend Region of a Stationary Gas Turbine Blade Ribbed Internal Cooling Duct

2005 ◽  
Vol 128 (4) ◽  
pp. 763-771 ◽  
Author(s):  
Evan A. Sewall ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Friction Factor ◽  
Flow Separation ◽  
Mean Flow ◽  
Dean Vortices ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
High Heat Transfer ◽  
Large Eddy

Large eddy simulation of the 180 deg bend in a stationary ribbed duct is presented. The domain studied includes three ribs upstream of the bend region and three ribs downstream of the bend with an outflow extension added to the end, using a total of 8.4 million cells. Two cases are compared to each other: one includes a rib in the bend and the other does not. The friction factor, mean flow, turbulence, and heat transfer are compared in the two cases to help explain the benefits and disadvantages of the wide number of flow effects seen in the bend, including flow separation at the tip of the dividing wall, counter-rotating Dean vortices, high heat transfer at areas of flow impingement, and flow separation at the upstream and downstream corners of the bend. Mean flow results show a region of separated flow at the tip of the dividing region in the case with no rib in the bend, but no separation region is observed in the case with a rib. A pair of counter-rotating Dean vortices in the middle of the bend is observed in both cases. Turbulent kinetic energy profiles show a 30% increase in the midplane of the bend when the rib is added. High gradients of heat transfer augmentation are observed on the back wall and downstream outside wall, where mean flow impingement occurs. This heat transfer is increased with the presence of a rib. Including a rib in the bend increases the friction factor in the bend by 80%, and it increases the heat transfer augmentation by approximately 20%, resulting in a trade-off between pressure drop and heat transfer.

Large Eddy Simulation of Flow and Heat Transfer in the 180° Bend Region of a Stationary Ribbed Gas Turbine Internal Cooling Duct

2005 ◽  
Author(s):  
Evan A. Sewall ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Flow Separation ◽  
Separated Flow ◽  
High Heat ◽  
Internal Cooling ◽  
Mean Flow ◽  
Dean Vortices ◽  
Heat Transfer Augmentation ◽  
High Heat Transfer

LES of the 180° bend in a stationary ribbed duct is presented. The domain studied includes three ribs upstream of the bend region and three ribs downstream of the bend with an outflow extension added to the end, using a total of 8.4 million cells. Two cases are compared to each other: one includes a rib in the bend and the other does not. The friction factor, mean flow, turbulence, and heat transfer are compared in the two cases to help explain the benefits and disadvantages of the wide number of flow effects seen in the bend, including flow separation at the tip of the dividing wall, counter-rotating Dean vortices, high heat transfer at areas of flow impingement, and flow separation at the upstream and downstream corners of the bend. Mean flow results show a region of separated flow at the tip of the dividing region in the case with no rib in the bend, but no separation region is observed in the case with a rib. A pair of counter-rotating Dean vortices in the middle of the bend is observed in both cases. Turbulent kinetic energy profiles show a 30% increase in the mid-plane of the bend when the rib is added. High gradients of heat transfer augmentation are observed on the back wall and downstream outside wall, where mean flow impingement occurs. This heat transfer is increased with the presence of a rib. Including a rib in the bend increases the friction factor in the bend by 80%, and it increases the heat transfer augmentation by approximately 20%, resulting in a tradeoff between pressure drop and heat transfer.

Large Eddy Simulation of Flow and Heat Transfer in a 90° Ribbed Duct With Rotation: Effect of Coriolis Forces

2004 ◽  
Author(s):  
Samer Abdel-Wahab ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Rotation Number ◽  
Mean Flow ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
A Value ◽  
Rotation Numbers ◽  
Large Eddy

This paper presents results from large eddy simulation (LES) of fully developed flow in a 90° ribbed duct with rib pitch-to-height ratio P/e = 10 and a rib height to hydraulic diameter ratio e/Dh = 0.1. Three rotation numbers Ro = 0.18, 0.35 and 0.67 are studied at a nominal Reynolds number based on bulk velocity of 20,000. Mean flow and turbulent quantities, together with heat transfer and friction augmentation data are presented. Turbulence and heat transfer are augmented on the trailing surface and reduced at the leading surface. The heat transfer augmentation ratio on the trailing surface asymptotes to a value of 3.7 ± 5% and does not show any further increasing trend as the rotation number increases beyond 0.2. On the other hand, augmentation ratios on the leading surface keep decreasing with an increase in rotation number with values ranging from 1.7 at Ro = 0.18 to 1.2 at Ro = 0.67. Secondary flow cells augment the heat transfer coefficient on the smooth walls by 20% to 30% over a stationary duct. An increase in rotation number from 0.35 to 0.67 decreases the frictional losses from an augmentation ratio of 9.6 to 8.75 and is a consequence of decrease in form drag and wall shear. Overall augmentation compared with a non-rotating duct ranges from +15% to +20% for heat transfer, and +10% to +15% for friction over the range of rotation numbers studied. Comparison of heat transfer augmentation with previous experimental results in the literature shows very good agreement.

Large Eddy Simulation of Flow and Heat Transfer in a Staggered 45° Ribbed Duct

2004 ◽  
Author(s):  
Samer Abdel-Wahab ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Secondary Flow ◽  
Mean Flow ◽  
Cross Sectional ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Rib Vortex

Results from large eddy simulation (LES) of fully developed flow in a staggered 45° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height to hydraulic diameter ratio e/Dh = 0.1. The nominal Reynolds number based on bulk velocity is 47,300. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow. Averaged velocity profiles at the duct center show excellent agreement with experiments and heat transfer predictions agree well with experiments. Turbulent kinetic energy, shear stress, and heat transfer augmentation ratios show a strong correlation to the rib vortex and the secondary flow. Overall, heat transfer is augmented by a factor of 2.3 compared with a smooth duct and matches experimental data within 2%.

Large Eddy Simulation of the Developing Region of a Stationary Ribbed Internal Turbine Blade Cooling Channel

2004 ◽  
Author(s):  
Evan A. Sewall ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Turbine Blade ◽  
Internal Cooling ◽  
Mean Flow ◽  
Heat Transfer Augmentation ◽  
The Third ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Cooling Passage

This study reports on a Large Eddy Simulation (LES) of the entrance section of a gas turbine blade internal cooling passage. The channel is fitted with in-line turbulators orthogonal to the flow, and the domain studied covers the first six ribs of the channel. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.1, and the rib pitch-to-rib height ratio (P/e) is 10. A constant temperature boundary condition is imposed on the walls and the ribs, and the flow Reynolds number is 20,000. Results indicate that the mean flow is essentially fully developed by the fifth rib. Turbulent kinetic energy near the ribbed wall approaches fully developed values very quickly by the third or fourth ribs. However, turbulent intensities at the center of the duct are not fully developed by the sixth rib. As a consequence, heat transfer augmentation on the ribbed walls reaches a fully developed state quickly after the third rib, whereas, the smooth wall heat transfer augmentation shows a slight but steady increasing trend toward the fully developed value up to the sixth rib. Both augmentation ratios are to within 10% of their fully developed values after the third rib.

Large Eddy Simulation Investigation of Flow and Heat Transfer in a Channel With Dimples and Protrusions

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Reynolds Numbers ◽  
Flow Acceleration ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Channel Form ◽  
Large Eddy ◽  
Dimple Surface

Large eddy simulation calculations are conducted for flow in a channel with dimples and protrusions on opposite walls with both surfaces heated at three Reynolds numbers, ReH=220, 940, and 9300, ranging from laminar, weakly turbulent, to fully turbulent, respectively. Turbulence generated by the separated shear layer in the dimple and along the downstream rim of the dimple is primarily responsible for heat transfer augmentation on the dimple surface. On the other hand, augmentation on the protrusion surface is mostly driven by flow impingement and flow acceleration between protrusions, while the turbulence generated in the wake has a secondary effect. Heat transfer augmentation ratios of 0.99 at ReH=220,2.9 at ReH=940, and 2.5 at ReH=9300 are obtained. Both skin friction and form losses contribute to pressure drop in the channel. Form losses increase from 45% to 80% with increasing Reynolds number. Friction coefficient augmentation ratios of 1.67, 4.82, and 6.37 are obtained at ReH=220, 940, and 9300, respectively. Based on the geometry studied, it is found that dimples and protrusions may not be viable heat transfer augmentation surfaces when the flow is steady and laminar.

Large Eddy Simulation in a Duct With Rounded Skewed Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Cross Section ◽  
Mean Flow ◽  
Cross Sectional ◽  
Square Duct ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Experimental Values

Results from Large Eddy Simulation (LES) of fully developed flow in a ribbed duct are presented with rib pitch-to-height ratio (P/e) is 10 and a rib height to hydraulic diameter ratio (e/Dh) is 0.1. Computations are carried out on a square duct with 45° ribs on the top and bottom walls arranged in a staggered fashion. The ribs have a rounded cross-section and are skewed at 45° to the main flow. The Reynolds number based on bulk velocity is 25,000. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented for a stationary case. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow and result in a spanwise variation of the heat transfer. The mean flow, the turbulent quantities and the heat transfer in the duct show similar trends as in the duct with square cross-section ribs. However the results show that there is lesser friction in the ducts with rounded ribs. The overall heat transfer on the ribbed wall was augmented by 2.85 times that of a smooth duct, at the cost of friction which increases by a factor of 10. The computed values compare well with the experimental values.

LES Investigation of Modified Rib Shapes on Heat Transfer in a Ribbed Duct

2021 ◽  
Author(s):  
K Sreekesh ◽  
Danesh K. Tafti ◽  
S Vengadesan
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Flow Direction ◽  
Internal Cooling ◽  
Square Duct ◽  
Flow Losses ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Internal cooling of gas turbine blade is critical for the durability of the blade material. One of the ways to accomplish this is by passing coolant through serpentine passages roughened with surface elements to enhance the heat transfer. In the present study, the traditional square rib (SQ-rib) placed normal to the flow direction is modified to a backward facing step rib (BS-rib) and a forward facing step rib (FS-rib). Large-eddy simulation (LES) is carried out for a square duct at Reb = 20000. Results show that the modified rib shapes result in substantial increase in heat transfer over the square rib with only a marginal increase in flow losses. The BS-rib shape produces the highest heat transfer augmentation followed by the FS-rib. The overall heat transfer augmentation for the BS-rib and FS-rib is 18% and 10% larger than the SQ-rib, respectively. Thermal-hydraulic performance is enhanced by 15%.

Large-eddy simulation of flow over a cylinder with from to : a skin-friction perspective

2017 ◽  
Vol 820 ◽  
pp. 121-158 ◽  
Author(s):  
W. Cheng ◽  
D. I. Pullin ◽  
R. Samtaney ◽  
W. Zhang ◽  
W. Gao
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Flow Separation ◽  
Skin Friction Coefficient ◽  
Cylinder Surface ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

We present wall-resolved large-eddy simulations (LES) of flow over a smooth-wall circular cylinder up to$Re_{D}=8.5\times 10^{5}$, where$Re_{D}$is Reynolds number based on the cylinder diameter$D$and the free-stream speed$U_{\infty }$. The stretched-vortex subgrid-scale (SGS) model is used in the entire simulation domain. For the sub-critical regime, six cases are implemented with$3.9\times 10^{3}\leqslant Re_{D}\leqslant 10^{5}$. Results are compared with experimental data for both the wall-pressure-coefficient distribution on the cylinder surface, which dominates the drag coefficient, and the skin-friction coefficient, which clearly correlates with the separation behaviour. In the super-critical regime, LES for three values of$Re_{D}$are carried out at different resolutions. The drag-crisis phenomenon is well captured. For lower resolution, numerical discretization fluctuations are sufficient to stimulate transition, while for higher resolution, an applied boundary-layer perturbation is found to be necessary to stimulate transition. Large-eddy simulation results at$Re_{D}=8.5\times 10^{5}$, with a mesh of$8192\times 1024\times 256$, agree well with the classic experimental measurements of Achenbach (J. Fluid Mech., vol. 34, 1968, pp. 625–639) especially for the skin-friction coefficient, where a spike is produced by the laminar–turbulent transition on the top of a prior separation bubble. We document the properties of the attached-flow boundary layer on the cylinder surface as these vary with$Re_{D}$. Within the separated portion of the flow, mean-flow separation–reattachment bubbles are observed at some values of$Re_{D}$, with separation characteristics that are consistent with experimental observations. Time sequences of instantaneous surface portraits of vector skin-friction trajectory fields indicate that the unsteady counterpart of a mean-flow separation–reattachment bubble corresponds to the formation of local flow-reattachment cells, visible as coherent bundles of diverging surface streamlines.

Turbulence Modeling Using Z-F, RSM, LES and WMLES for Flow Analysis in Z-Shape Ducts

2020 ◽  
Author(s):  
Mohammed Karbon ◽  
Ahmad K. Sleiti
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Large Eddy Simulation ◽  
Flow Separation ◽  
Temporal Variations ◽  
Mean Flow ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rsm Model

Abstract Turbulent flow in Z-shape duct configuration is investigated and analyzed using Reynolds Stress Model (RSM), Large Eddy Simulation (LES), ζ-f Model, and Wall-Modeled Large Eddy Simulation (WMLES). The results are validated and compared to experimental data. Both RSM and ζ-f models are based on steady-state RANS solutions, while LES and WMLES models account for temporal variations transient behavior of the flow turbulence. The focus was on regions where RSM has over or under predicted the flow and regions where there are flow separations and high turbulence. LES simulation results have shown under-prediction and over-prediction in the flow separation and re-attachment regions. It is found that the turbulent kinetic energy production in ζ equation is much easier to reproduce accurately than other models. Both mean velocity gradient and local turbulent stress terms are also much easier to resolve properly. The current research has found that ζ-f model not only takes less time to complete the simulation but also the mean flow velocity profile results are in better agreement with experimental data than RSM model despite both are coupled steady-state RANS. ζ-f model numerically resolved both the flow separation and re-attachment regions better than RSM model. WMLES model is employed to investigate the SGS model impact on the small eddies dissipated from the large eddies. Such WMLES model produces much better results than the LES model, however the SGS viscosity damps the energy of the flow.

Large Eddy Simulation of Two-Dimensional Jet Impingement Heat Transfer Enhanced by Submilli-Scale Ribs

2013 ◽  
Author(s):  
Yutaka Oda ◽  
Kenichiro Takeishi
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Eddy Simulation ◽  
Impingement Heat Transfer ◽  
High Heat Transfer ◽  
Large Eddy

Two-dimensional jet impingement heat transfer enhanced by submilli-scale ribs has been studied by mass transfer experiments and large eddy simulations. Installation of ribs induces flow separation and reattachment, and realize high heat transfer coefficient in the wall jet region. Higher rib-height was found to be effective to make the enhanced heat transfer region larger. Large eddy simulation was found to predict reattachment length correctly, which then resulted in good agreement of local heat transfer coefficients between experiment and simulations except the stagnation and reattachment regions, where over- and under-estimation occurs.

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