Assessment of turbulence models for low Reynolds number flows and their computational costs, Part 2: Square prism in cross flow

2021 ◽  
pp. 1-38
Author(s):  
Thomas Mancuso ◽  
Abhijit Mukherjee
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Low Reynolds Number ◽  
Cross Flow ◽  
Tube Bank ◽  
Computational Costs ◽  
Square Prism ◽  
Sst Model

Abstract The accuracy of six turbulent flow modeling techniques in an unsteady solution is evaluated against experimental data for a square prism in cross flow. The selected models; SST, SST-SAS, RSM, PANS-SST, DES and LES models are the same as those presented in Part 1 of this study, which focused on flow in a staggered tube bank. For this geometry, the SST model proved to be effective at capturing the averaged Nusselt values per side of the square with relatively low computational costs. The SST model however showed poorer fidelity to the local Nusselt number profile compared to the experimental data. The LES approach provided a more accurate representation of the local Nusselt number but the computational cost was significantly higher. The PANS modification to the SST model did provide a noticeable improvement in accuracy at a reasonable cost while the SAS modification did not see the same improvement. These conclusions are generally consistent with those found for the staggered tube bank in Part 1 of this study. This study can be used as a guide for the industrial user to select a turbulence model for a similar problem with a low Reynolds number and significant flow separation.

Hydrodynamic Characteristics of Flow around Tube Bank with Integral Wake Splitter

2014 ◽  
Vol 660 ◽  
pp. 649-653
Author(s):  
Suzairin bin Md Seri ◽  
Zainal Ambri bin Abdul Karim ◽  
Hamidon bin Salleh ◽  
Mohd Faizal Mohideen Batcha ◽  
Vijay R. Raghavan
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Static Pressure ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Hydrodynamic Characteristics ◽  
Rectangular Duct ◽  
Tube Bank ◽  
Static Pressure Distribution ◽  
Tube Banks

This paper reports the effects of a longitudinal plate attached at the backward stagnation point of a bank of tubes on the local static pressure distribution. The longitudinal plate is termed as an integral wake splitter. Investigations on hydrodynamic characteristics of tube banks with integral wake splitter were carried out in cross flow of air in a rectangular duct at a Reynolds number of 15950. The integral wake splitter length-to-tube-diameter ratios studied were 0.5, 1.0, 1.5 and 2.0. The tube bank consisting of 12 rows and 3 tubes per row in equilateral triangular arrangement with a transverse pitch to diameter ratio, a = 2. The results obtained were compared to the experimental data of Seri et al. (2014). It is observed that the addition of the integral wake splitter reduces the overall pressure drop.

scholarly journals Analysis of transient mixed convection in a horizontal channel partially heated from below

2021 ◽  
Vol 4 (8(112)) ◽  
pp. 16-22
Author(s):  
Mahmoud A. Mashkour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Source ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Stokes Equations ◽  
Heat Convection ◽  
Horizontal Channel ◽  
Outlet Temperature

The heat convection phenomenon has been investigated numerically (mathematically) for a channel located horizontally and partially heated at a uniform heat flux with forced and free heat convection. The investigated horizontal channel with a fluid inlet and the enclosure was exposed to the heat source from the bottom while the channel upper side was kept with a constant temperature equal to fluid outlet temperature. Transient, laminar, incompressible and mixed convective flow is assumed within the channel. Therefore, the flow field is estimated using Navier Stokes equations, which involves the Boussinesq approximation. While the temperature field is calculated using the standard energy model, where, Re, Pr, Ri are Reynolds number, Prandtl number, and Richardson number, respectively. Reynolds number (Re) was changed during the test from 1 to 50 (1, 10, 25, and 50) for each case study, Richardson (Ri) number was changed during the test from 1 to 25 (1, 5, 10, 15, 20, and, 25). The average Nusselt number (Nuav) increases exponentially with the Reynold number for each Richardson number and the local Nusselt number (NuI) rises in the heating point. Then gradually stabilized until reaching the endpoint of the channel while the local Nusselt number increases with a decrease in the Reynolds number over there. In addition, the streamlines and isotherms patterns in case of the very low value of the Reynolds number indicate very low convective heat transfer with all values of Richardson number. Furthermore, near the heat source, the fluid flow rate rise increases the convection heat transfer that clarified the Nusselt number behavior with Reynolds number indicating that maximum Nu No. are 6, 12, 27 and 31 for Re No. 1, 10, 25 and 50, respectively

Performance characteristics of a chilled water spirally coiled finned tube in cross flow for air conditioning applications

2012 ◽  
Vol 227 (2) ◽  
pp. 320-331 ◽  
Author(s):  
Abdalla Gomaa ◽  
Wael IA Aly ◽  
Ashraf Mimi Elsaid ◽  
Eldesuki I Eid
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Flow Direction ◽  
Cross Flow ◽  
Finned Tube ◽  
Performance Characteristics ◽  
Curvature Ratio ◽  
Coiled Tube ◽  
Chilled Water

In the present study, the thermo-fluid characteristics of a spirally coiled finned tube in cross flow were experimentally investigated. This investigation covered different design parameters such as curvature ratio, air velocity, flow direction, fin pitch and flow rate of chilled water on performance characteristics of the spirally coiled finned tube. The purpose was to evaluate this kind of the spirally finned-tube cooling coils with particular reference to bare coiled tube. Six test specimens were designed and manufactured with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30 mm and fin pitches of (33, 22, 11 mm). Experiments were carried out in a pilot wind tunnel with air Reynolds number ranging from 35,500 to 245,000. Two types of chilled water flow directions entering the spiral coil were tested at Reynolds number ranging from 5700 to 25,300, the first was inward flow direction and the other was to outward flow direction. The results revealed that the inward flow direction has significant enhancement effect on the Nusselt number compared with outward flow direction by 37.0% for tube pitch of 18 mm and curvature ratio of 0.027. The decrease of fin pitch enhances the Nusselt number by 21.92% on expense of friction factor by 10.9%. In the case of spirally coiled bare tube, the decreasing of the curvature ratio increases air side Nusselt number by 33.69% on expense of friction factor by 18.36%. General correlations of Nusselt number and air friction factor for bare and finned spirally coiled tube were correlated based on reported experimental data.

Thermal Optimal Design for Multichip Module Disks With an Unconfined Round-Jet Impingement

2005 ◽  
Author(s):  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. C. Lee ◽  
Y. H. Hung
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Steady State ◽  
Thermal Performance ◽  
Jet Impingement ◽  
Separation Distance ◽  
Grashof Number ◽  
Round Jet ◽  
Space Limitation

An effective method for performing the thermal optimization of stationary and rotating MCM disks with an unconfined round-jet impingement under space limitation constraint has been successfully developed. The design variables of stationary and rotating MCM disks with an unconfined round-jet impingement include: the ratio of jet separation distance to nozzle diameter (H/d), steady-state Grashof number (Grs), jet Reynolds number (Rej), rotational Reynolds number (Rer). The total experimental cases for stationary and rotating MCM disks are statistically designed by the Central Composite Design (CCD) method. In addition, a sensitivity analysis, the so-called ANOVA, for the design factors has been performed. In the stationary MCM disk with an unconfined round-jet impingement, the contribution percentage of jet Reynolds number on the thermal performance is 95.86%. The effect of jet Reynolds numbers on chip temperature distribution is more significant than that of the H/d ratio and steady-state Grashof number. In rotating MCM disk with an unconfined round-jet impingement, the effect of jet Reynolds number, which has the contribution percentage of 91.81%, dominates the thermal performance. Furthermore, the comparisons between the predictions by using the quadratic Response Surface Methodology (RSM) and the experimental data are made. The maximum deviations for transient stagnation Nusselt number and transient average Nusselt number for the cases of stationary MCM disk are 10.05% and 11.82%, respectively; and 9.41% and 12.44% for the cases of rotating MCM disk, respectively. Finally, with the Sequential Quadratic Programming (SQP) technique, a series of thermal optimal designs under space limitation constraint H/d≤12 has been efficiently performed. Comparisons between the numerical optimization results and the experimental data are made with a satisfactory agreement.

A Comparative Study of Performance of Low Reynolds Number Turbulence Models for Various Heat Transfer Enhancement Simulations

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ankit Tiwari ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Transfer Enhancement ◽  
Low Reynolds

The goal of this study is to evaluate the computational fluid dynamic (CFD) predictions of friction factor and Nusselt number from six different low Reynolds number k–ε (LRKE) models namely Chang–Hsieh–Chen (CHC), Launder–Sharma (LS), Abid, Lam–Bremhorst (LB), Yang–Shih (YS), and Abe–Kondoh–Nagano (AKN) for various heat transfer enhancement applications. Standard and realizable k–ε (RKE) models with enhanced wall treatment (EWT) were also studied. CFD predictions of Nusselt number, Stanton number, and friction factor were compared with experimental data from literature. Various parameters such as effect of type of mesh element and grid resolution were also studied. It is recommended that a model, which predicts reasonably accurate values for both friction factor and Nusselt number, should be chosen over disparate models, which may predict either of these quantities more accurately. This is based on the performance evaluation criterion developed by Webb and Kim (2006, Principles of Enhanced Heat Transfer, 2nd ed., Taylor and Francis Group, pp. 1–72) for heat transfer enhancement. It was found that all LRKE models failed to predict friction factor and Nusselt number accurately (within 30%) for transverse rectangular ribs, whereas standard and RKE with EWT predicted friction factor and Nusselt number within 25%. Conversely, for transverse grooves, AKN, AKN/CHC, and LS (with modified constants) models accurately predicted (within 30%) both friction factor and Nusselt number for rectangular, circular, and trapezoidal grooves, respectively. In these cases, standard and RKE predictions were inaccurate and inconsistent. For longitudinal fins, Standard/RKE model, AKN, LS and Abid LRKE models gave the friction factor and Nusselt number predictions within 25%, with the AKN model being the most accurate.

scholarly journals Prediction of Heat Transfer For Turbulent Flow in Rotating Radial Duct

1995 ◽  
Vol 2 (1) ◽  
pp. 51-58
Author(s):  
P. Tekriwal
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Turbulence Model ◽  
High Reynolds Number ◽  
Low Reynolds Number ◽  
Rotating Flows ◽  
Wall Function ◽  
Model Predictions ◽  
High Reynolds

The objective of the current modeling effort is to validate the numerical model and improve upon the prediction of heat transfer in rotating systems. Low-Reynolds number turbulence model (without the wall function) has been employed for three-dimensional heat transfer predictions for radially outward flow in a square cooling duct rotating about an axis perpendicular to its length. Computations are also made using the standard and extended high-Reynolds number kturbulence models (in conjunction with the wall function) for the same flow configuration. The results from all these models are compared with experimental data for flows at different rotation numbers and Reynolds number equal to 25,000. The results show that the low-Reynolds number model predictions are not as good as the high-Re model predictions with the wall function. The wall function formulation predicts the right trend of heat transfer profile and the agreement with the data is within 30% or so for flows at high rotation number. Since the Navier-Stokes equations are integrated all the way to wall in the case of low-Re model, the computation time is relatively high and the convergence is rather slow, thus rendering the low-Re model as an unattractive choice for rotating flows at high Reynolds number.The extended k-ε turbulence model is also employed to compute heat transfer for rotating flows with uneven wall temperatures and uniform wall heat flux conditions. The comparison with the experimental data available in literature shows that the predictions on both the leading wall and the trailing wall are satisfactory and within 5-25% agreement.

Effects of Dimple Depth on Nusselt Numbers and Friction Factors for Internal Cooling in a Channel

2004 ◽  
Author(s):  
N. K. Burgess ◽  
P. M. Ligrani
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Height ◽  
Stagnation Temperature ◽  
Nusselt Numbers ◽  
Number Ratio ◽  
Friction Factors

Experimental results, measured on dimpled test surfaces placed on one wall of different channels, are given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers based on channel height from 9,940 to 74,800. The data presented include friction factors, local Nusselt numbers, spatially-averaged Nusselt numbers, and globally-averaged Nusselt numbers. The ratios of dimple depth to dimple print diameter δ/D are 0.1, 0.2, and 0.3 to provide information on the influences of dimple depth. The ratio of channel height to dimple print diameter is 1.00. At all Reynolds numbers considered, local and spatially-resolved Nusselt number augmentations increase as dimple depth increases (and all other experimental and geometric parameters are held approximately constant). These are attributed to: (i) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (ii) increases in the magnitudes of three-dimensional turbulence production and turbulence transport. The effects of these phenomena are especially apparent in local Nusselt number ratio distributions measured just inside of the dimples, and just downstream of the downstream edges of the dimples. Data are also presented to illustrate the effects of Reynolds number, and streamwise development for δ/D = 0.1 dimples. Significant local Nusselt number ratio variations are observed at different streamwise locations, whereas variations with Reynolds number are mostly apparent on flat surfaces just downstream of individual dimples.

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