Large Eddy Simulation of Fully Developed Flow and Heat Transfer in a Rotating Duct With 45° Ribs

2006 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Outer Wall ◽  
High Heat ◽  
Wall Turbulence ◽  
Square Duct ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
Large Eddy

This paper concerns itself with investigating the effect of rotation on flow and heat transfer in a 45° ribbed square duct. Large-Eddy Simulations (LES) are used to investigate why rotation does not have any effect on heat transfer augmentation unlike 90 degree ribs, in which considerable changes are observed in augmentation at the trailing and leading walls of the duct. It is found that unlike 90 degree ribbed ducts, in which the heat transfer augmentation is strongly dependent on streamwise momentum, spanwise momentum dominates heat transfer in skewed ribs. Since Coriolis forces under orthogonal rotation about the z-axis do not directly contribute to spanwise momentum, they do not have as much of an effect on heat transfer at the ribbed walls at the trailing and leading sides. However, because of the augmentation of turbulence at the trailing side, the vortices which are produced in the separated shear layer of the rib and which move from the inside to the outside of the duct, break down and diffuse before they can impinge on the outer wall. Turbulence attenuation at the leading wall has the opposite effect which allows the vortices to maintain their coherence and impinge on the outer wall. This effect taken together with the streamwise flow being pushed to the leading side, produces an extended region of high heat transfer at the outer wall near the leading side. This is countered by lower heat transfer at the trailing side of the outer wall. Hence, although local variations are present due to rotation, the overall augmentation remains the same.

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 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.

Constrained large-eddy simulation of turbulent flow and heat transfer in a stationary ribbed duct

2016 ◽  
Vol 26 (3/4) ◽  
pp. 1069-1091 ◽  
Author(s):  
Zhou Jiang ◽  
Zuoli Xiao ◽  
Yipeng Shi ◽  
Shiyi Chen
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Thermodynamic Quantities ◽  
Detached Eddy Simulation ◽  
Square Duct ◽  
Content Type ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Purpose – The knowledge about the heat transfer and flow field in the ribbed internal passage is particularly important in industrial and engineering applications. The purpose of this paper is to identify and analyze the performance of the constrained large-eddy simulation (CLES) method in predicting the fully developed turbulent flow and heat transfer in a stationary periodic square duct with two-side ribbed walls. Design/methodology/approach – The rib height-to-duct hydraulic diameter ratio is 0.1 and the rib pitch-to-height ratio is 9. The bulk Reynolds number is set to 30,000, and the bulk Mach number of the flow is chosen as 0.1 in order to keep the flow almost incompressible. The CLES calculated results are thoroughly assessed in comparison with the detached-eddy simulation (DES) and traditional large-eddy simulation (LES) methods in the light of the experimentally measured data. Findings – It is manifested that the CLES approach can predict both aerodynamic and thermodynamic quantities more accurately than the DES and traditional LES methods. Originality/value – This is the first time for the CLES method to be applied to simulation of heat and fluid flow in this widely used geometry.

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%.

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

2006 ◽  
Author(s):  
M. Elyyan ◽  
A. Rozati ◽  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbulent Energy ◽  
Channel Height ◽  
Height Ratio ◽  
Pressure Drag ◽  
Heat Transfer Augmentation ◽  
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.

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 and Heat Transfer in a 90° Ribbed Duct With Rotation: Effect of Coriolis and Centrifugal Buoyancy Forces

2004 ◽  
Author(s):  
Samer Abdel-Wahab ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Rotation Effect ◽  
Fully Developed Flow ◽  
Flow Cells ◽  
Coriolis Forces ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Rotation Numbers ◽  
Large Eddy

Results from large eddy simulations (LES) of fully developed flow in a 90° 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. Three rotation numbers Ro = 0.18, 0.36 and 0.68 are studied at a nominal Reynolds number based on bulk velocity of 20,000. Centrifugal buoyancy effects are included at two Richardson numbers of Ri = 12, 28 (Buoyancy number, Bo = 0.12 and 0.30) for each rotation case. Buoyancy strengthens the secondary flow cells in the duct cross-section which leads to an increase of 20% to 30% in heat transfer augmentation at the smooth walls over and above the effect of Coriolis forces. Buoyancy also accentuates the augmentation of turbulence near the trailing wall of the duct and increases the heat transfer augmentation ratio 10% to 20% over the action of Coriolis forces alone. However, it does not have any significant effect at the leading side of the duct. The overall effect of buoyancy on heat transfer augmentation for the ribbed duct is found to be less than 10% over the effect of Coriolis forces alone. Friction on the other hand is augmented 15% to 20% at the highest buoyancy number studied. Comparison with available experiments in the literature show excellent agreement.

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 an Internal Cooling Duct With High Blockage Ratio 45° Staggered Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti ◽  
Samer Abdel-Wahab
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Flow Direction ◽  
Outer Wall ◽  
Internal Cooling ◽  
Square Duct ◽  
Square Channel ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Numerical Predictions

Numerical predictions of a hydrodynamic and thermally developed turbulent flow are presented for a unit period of a stationary duct with square ribs aligned at 45° to the main flow direction. The rib height to channel hydraulic diameter (e/Dh) is 0.375 and the rib pitch to rib height (P/e) is 10. The domain under consideration is a rectangular passage of aspect ratio 1:2.5 with 45° ribs on the top and bottom walls arranged in a staggered fashion. The computations are carried out for a bulk Re of 27,000. The rib geometry introduces a strong secondary flow along the rib. A large helical vortex develops behind the rib which breaks down before it reaches the outer wall. This results in higher heat transfer at the inner wall as compared to the outer wall, which is in contrast to the trend observed in a square channel with low blockage ribs. In a square duct with low blockage ribs the secondary flow has two counter-rotating cells which do not change direction through the channel. However in this case only one rotating cell is observed in this case, which changes direction as it passes over successive ribs. The average friction and the heat transfer augmentation ratios are consistent with the experimental results [1], predicting values within 15% of the measured quantities.

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