Verification of RANS for Analyzing Convective Cooling System With and Without Ribs

2009 ◽  
Author(s):  
Wei Chen ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Turbulence Model ◽  
Cooling System ◽  
Reynolds Numbers ◽  
Convective Cooling ◽  
Turn Region ◽  
Good Agreement ◽  
Rans Method

Accurate prediction of pressure drop and heat transfer in convective cooling system is of importance to gas turbine industry. In the present paper, a detailed study and assessment of RANS method based on SST reattach turbulence model is performed on a convective cooling system in three kinds of U-duct: smooth, with 45 degree or 90 degree angled parallel ribs. Heat transfer and pressure drop distributions in the ducts are analyzed spatially at the Reynolds numbers of 15000, 30000 and 60000. The numerical results are compared with the experimental data and the empirical correlation from Han et al. It is found that the obtained pressure drop distribution based on RANS with SST reattach turbulence model matches the experimental data for all the U-ducts adequately. Meanwhile, the heat transfer is well predicted by the RANS method in the cases of smooth duct and 45 degree ribbed duct. A good agreement is obtained in the turn region of 45 degree ribbed duct, it owes to the strong secondary flow induced by ribs, which restrain the mainstream to separate and accelerate in the turn. But, the heat transfer is significantly under-predicted for 90 degree ribbed duct since the flow reattachment point between the ribs is predicted farther away from the upstream rib than that in the experiment. Therefore, it is suggested that the RANS method with a suitable turbulence model is valuable for the smooth and 45 degree ribbed U-duct with the acceptable engineering accuracy. But the prediction of heat transfer in 90 degree ribbed U-duct is still a challenge for the RANS to solve.

Effect of Turning Vane Configurations on Heat Transfer and Pressure Drop in a Ribbed Internal Cooling System

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Wei Chen ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulence Model ◽  
Cooling System ◽  
Turbulence Models ◽  
Loss Coefficient ◽  
Test Cases ◽  
Convective Cooling ◽  
Blade Cooling ◽  
Turn Region

The ribbed serpentine blade cooling system is a typical configuration in the modern gas turbine airfoil. In this study, experimental and the numerical efforts were carried out to investigate the local heat transfer and pressure drop distribution of a ribbed blade cooling system with different configurations in the turn region. A test rig containing a ribbed rectangular U-duct with a 180 deg round turn was built in Tsinghua University for this study. The transient liquid crystal method was applied to get the heat transfer distribution. Nine test cases with three turn configurations under three Reynolds numbers were carried out in the experiment. Pressure was measured along the duct in order to determine the influence of turning vane configurations on pressure drop. The test cases were also analyzed numerically based on Reynolds-averaged Navier-Stokes (RANS) with three different turbulence models: the k-ε model, the SST reattachment model, and the Omega Reynolds stress (ORS) turbulence model. Both the experimental and numerical results showed a significant influence of the turning vane configuration on the heat transfer and pressure drop in the convective cooling channel. Among the three configurations, the loss coefficient of turn in configuration 2 was lowest due to the introduction of turning vane. Even the ribs were added in the turn region of configuration 3, the loss coefficient and friction factor are reduced by 23% and 17.5%, respectively. Meanwhile, the heat transfer in baseline configuration is still the highest. As the introduction of turning vane, the heat transfer in the region after turn was reduced by 35%. In configuration 3, the heat transfer in the turn region was enhanced by 15% as the ribs installed in the turn region. In the before turn region, the pressure drop and heat transfer was not influenced by the turn configuration. All the turbulence models captured the trend of heat transfer and pressure drop distribution of three test sections correctly, but all provide overpredicted heat transfer results. Among the models, the ORS turbulence model provided the best prediction. While aiming at high heat transfer level and low pressure drop, it is suggested that a suitable turn configuration, especially with the turning vane and/or the ribs, is a promising way to meet the conflicted requirements of the heat transfer and pressure drop in the convective cooling system.

Effect of Turning Vane Configurations on Heat Transfer and Pressure Drop in a Ribbed Internal Cooling System

2010 ◽  
Author(s):  
Wei Chen ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulence Model ◽  
Cooling System ◽  
Turbulence Models ◽  
Loss Coefficient ◽  
Test Cases ◽  
Convective Cooling ◽  
Blade Cooling ◽  
Turn Region

The ribbed serpentine blade cooling system is a typical configuration in the modern gas turbine airfoil. In this study, the experimental and the numerical efforts were carried out to investigate the local heat transfer and pressure drop distribution of a ribbed blade cooling system with different configurations in the turn region. A test rig containing a ribbed rectangular U-duct with a 180° round turn was built in Tsinghua University for this study. Transient liquid crystal method was applied to get the heat transfer distribution. Nine test cases with three turn configurations under three Reynolds numbers were carried out in the experiment. Pressure was measured along the duct in order to determine the influence of turning vane configurations on pressure drop. The test cases were also analyzed numerically based on RANS with three different turbulence models: the k-ε model, the SST reattachment model, and the Omega Reynolds Stress turbulence model. Both the experimental and the numerical results showed a significant influence of the turning vane configuration on the heat transfer and pressure drop in the convective cooling channel. Among the three configurations, the loss coefficient of turn in configuration 2 was lowest, due to the introduction of turning vane. Even the ribs were added in turn region of configuration 3, the loss coefficient and friction factor are reduced by 23% and 17.5%, respectively. Meanwhile, the heat transfer in baseline configuration is still the highest. As the introduction of turning vane, the heat transfer in the region after turn was reduced by 35%. In configuration 3, the heat transfer in the turn region was enhanced by 15% as the ribs installed in the turn region. In the before turn region, the pressure drop and heat transfer was not influenced by the turn configuration. All the turbulence models captured the trend of heat transfer and pressure drop distribution of three test sections correctly, but all provide overpredicted heat transfer results. Among the models, the ORS turbulence model provided the best prediction. While aiming at high heat transfer level and low pressure drop, it is suggested that, a suitable turn configuration, especially with the turning vane and/or the ribs, is a promising way to meet the conflicted requirements of the heat transfer and pressure drop in the convective cooling system.

scholarly journals Influence of fin thickness on heat transfer and flow performance of a parallel flow evaporator

2019 ◽  
Vol 23 (4) ◽  
pp. 2413-2419 ◽  
Author(s):  
Haijun Li ◽  
Enhai Liu ◽  
Guanghui Zhou ◽  
Fengye Yang ◽  
Zhiyong Su ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Comprehensive Evaluation ◽  
Reynolds Numbers ◽  
Parallel Flow ◽  
Heat Transfer Factor ◽  
Heat Transfer Capacity ◽  
Fin Thickness ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

This paper studies numerically the influence of the louver?s fin thickness on heat transfer and flow performance of a parallel flow evaporator, a comprehensive evaluation and analysis of the five structures at different Reynolds numbers are systematically carried out. Comparison of the numerical results with the experimental data shows good agreement with maximal errors of 12.16% and 5.29% for the heat transfer factor and the resistance factor, respectively. The results show that the heat transfer coefficient and the pressure drop increase with the increase of the thickness of the louver fins when the Reynolds number is a constant. The analysis of the comprehensive evaluation factor shows that the A-type fin is the best, and it can effectively strengthen the heat exchange on the air side and improve the heat transfer capacity of the system. The research results can provide reference for the structural optimization of the louver fins.

Effects of 3-D Local Unsteadiness on Heat Transfer Prediction in Turbulated Passages

2003 ◽  
Author(s):  
Pamela A. McDowell ◽  
William D. York ◽  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Successful Outcome ◽  
Small Scale ◽  
Cross Sectional ◽  
Fully Implicit

A newly developed unsteady turbulence model was used to predict heat transfer in a turbulated passage typical of turbine airfoil cooling applications. Comparison of fullyconverged computational solutions to experimental measurements reveal that accurate prediction of heat transfer coefficient requires the effects of local small-scale unsteadiness to be captured. Validation was accomplished through comparison of the time- and area-averaged Nusselt number on the passage wall between adjacent ribs with experimental data from the open literature. The straight channel had a square cross-sectional area with multiple rows of staggered and rounded-edge ribs on opposite walls that were orthogonal to the flow. Simulations were run for Reynolds numbers of 5500, 16500, and 25000. Computational solutions were obtained on a multi-block, multi-topology, unstructured, and adaptive grid, using a pressure-correction based, fully-implicit Navier-Stokes solver. The computational results include two-dimensional (2-D) and three-dimensional (3-D) steady and unsteady simulations with viscous sublayers resolved (y+ ≤ 1) on all the walls in every case. Turbulence closure was obtained using a new turbulence model developed in-house for the unsteady simulations, and a realizable k-ε turbulence model was used for the steady simulations. The results obtained from the unsteady simulations show greatly improved agreement with the experimental data, especially at realistically high Reynolds numbers. The key 3-D physics mechanisms responsible for the successful outcome include: (1) shear layer roll-up over the turbulators; (2) recirculation zones both upstream and downstream of the rib faces; and (3) reattachment regions between each rib pair. Results from the unsteady case are superior to those of the steady because they capture the aforementioned mechanisms, and therefore more accurately predict the heat transfer.

scholarly journals Internal Passage Heat Transfer Prediction Using Multiblock Grids and a k-ω Turbulence Model

1996 ◽  
Author(s):  
David L. Rigby ◽  
A. A. Ameri ◽  
E. Steinthorsson
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Three Dimensional Flow ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Single Block ◽  
Multiblock Grid ◽  
Good Agreement

Numerical simulations of the three-dimensional flow and heat transfer in a rectangular duct with a 180° bend were performed. Results are presented for Reynolds numbers of 17,000 and 37,000 and for aspect ratios of 0.5 and 1.0. A k-ω turbulence model with no reference to distance to a wall is used. Direct comparison between single block and multiblock grid calculations are made. Heat transfer and velocity distributions are compared to available literature with good agreement. The multi-block grid system is seen to produce more accurate results compared to a single-block grid with the same number of cells.

Numerical Prediction of Heat Transfer in a Channel With Ribs and Bleed

1997 ◽  
Author(s):  
David L. Rigby ◽  
E. Steinthorsson ◽  
A. A. Ameri
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Turbulence Model ◽  
Comparative Evaluation ◽  
Reynolds Numbers ◽  
Structured Grids ◽  
Complicated Geometries ◽  
Block Approach ◽  
Number Of Cells ◽  
Good Agreement

In the present work numerical simulations for flow in a straight channel with square cross section is presented. While three of the walls of the channel are smooth the remaining wall was simulated to possess a combination of ribs and bleed holes. To allow for a comparative evaluation of the said heat transfer promoters that same wall was also simulated with holes only; ribs only; or simply smooth. Reynolds numbers from 10,000 to 38,000 based on the hydraulic diameter were considered. Very general multi-block structured grids were used to allow good grid quality around ribs and into the holes, and also to minimize the number of cells required. Turbulence was accounted for by a k-ω turbulence model which does not require reference to distance to a wall. Good agreement with experimental results demonstrate that the structured multi-block approach with the k-ω turbulence model is efficient and viable even for very complicated geometries.

Measurement and Modeling of Confined Jet Discharged Tangentially on a Concave Semicylindrical Hot Surface

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Mohammad O. Hamdan ◽  
Emad Elnajjar ◽  
Yousef Haik
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Heated Surface ◽  
Turbulence Models ◽  
Infrared Camera ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Reynolds Stress Model ◽  
Outlet Flow

The paper investigates experimentally and numerically the heat transfer augmentation from a semicircular heated surface due to confined slot-jet impingement. For different Reynolds numbers, the average and local Nusselt numbers are calculated by reporting the heater thermal image obtained by an infrared camera, the inlet and outlet flow temperature via thermocouples, the flow rate via rotameter, and the pressure drop across the inlet and outlet flow via pressure transducers. The single enclosed jet flow is used to create a single cyclone inside the internal semicircular channel to promote the heat transfer at different jet Reynolds numbers (Rejet = 1000–5000). Three turbulence models, namely, the standard k – ɛ, k – ω and the Reynolds stress model (RSM) have been investigated in the present paper by comparing Nusselt number and normalized pressure drop distribution against the experimental data, helping ascertain on the relative merits of the adopted models. The computational fluid dynamics results show that the RSM turbulent model reasonably forecast the experimental data.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 557-563 ◽  
Author(s):  
Paul L. Sears ◽  
Libing Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Drag Reducing Additive ◽  
Good Agreement

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.

Predictions of the Effect of Roughness on Heat Transfer From Turbine Airfoils

1998 ◽  
Author(s):  
Anil K. Tolpadi ◽  
Michael E. Crawford
Keyword(s):  
Heat Transfer ◽  
Side Surface ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Surface Finishing ◽  
Transfer Coefficients ◽  
Average Roughness ◽  
Wide Range ◽  
Turbine Airfoils ◽  
Good Agreement

The heat transfer and aerodynamic performance of turbine airfoils are greatly influenced by the gas side surface finish. In order to operate at higher efficiencies and to have reduced cooling requirements, airfoil designs require better surface finishing processes to create smoother surfaces. In this paper, three different cast airfoils were analyzed: the first airfoil was grit blasted and codep coated, the second airfoil was tumbled and aluminide coated, and the third airfoil was polished further. Each of these airfoils had different levels of roughness. The TEXSTAN boundary layer code was used to make predictions of the heat transfer along both the pressure and suction sides of all three airfoils. These predictions have been compared to corresponding heat transfer data reported earlier by Abuaf et al. (1997). The data were obtained over a wide range of Reynolds numbers simulating typical aircraft engine conditions. A three-parameter full-cone based roughness model was implemented in TEXSTAN and used for the predictions. The three parameters were the centerline average roughness, the cone height and the cone-to-cone pitch. The heat transfer coefficient predictions indicated good agreement with the data over most Reynolds numbers and for all airfoils-both pressure and suction sides. The transition location on the pressure side was well predicted for all airfoils; on the suction side, transition was well predicted at the higher Reynolds numbers but was computed to be somewhat early at the lower Reynolds numbers. Also, at lower Reynolds numbers, the heat transfer coefficients were not in very good agreement with the data on the suction side.

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