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.

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

1997 ◽  
Author(s):  
Bernhard Bonhoff ◽  
Uwe Tomm ◽  
Bruce V. Johnson ◽  
Ian Jennions
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Computational Study ◽  
Flow Direction ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Flow Conditions

A computational study was performed for the flow and heat transfer in rotating coolant passages with two legs connected with a U-bend. The dimensionless flow conditions and the rotational speed were typical of those in the internal cooling passages of turbine blades. The calculations were performed for two geometries and flow conditions for which experimental heat transfer data were obtained under the NASA HOST project. The first model had smooth surfaces on all walls. The second model had opposing ribs staggered and angled at 45 deg. 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. Results from these calculations were compared with the previous measurements as well as with previous calculations for the nonrotating models at a Reynolds number of 25,000 and a rotation number of 0.24. At these conditions, the predicted heat transfer is known to be strongly influenced by the turbulence and wall models. The differential Reynolds-stress model (RSM) was used for the calculation. Local heat transfer results are presented as well as results averaged over wall segments. The averaged heat transfer predictions were close to the experimental results in the first leg of the channel, while the heat transfer in the second leg was overestimated by RSM. The flow field results showed a large amount of secondary flow in the channels with rotational velocities as large as 90 percent of the mean value. These secondary flows were attributed to the buoyancy effects, the Coriolis forces, the curvature of the bend and the orientation of the skewed ribs. Details of the flow field are discussed. Both the magnitude and the change of the heat transfer were captured well with the calculations for the rotating cases.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

Conjugate Heat Transfer Simulation and Entropy Generation Analysis of Gas Turbine Blades

2021 ◽  
Author(s):  
Yaping Ju ◽  
Yi Feng ◽  
Chuhua Zhang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Entropy Generation ◽  
Conjugate Heat Transfer ◽  
Turbine Blades ◽  
Measurement Data ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Gas Turbine Blades ◽  
Internally Cooled

Abstract Reynolds averaged Navier-Stokes model-based conjugate heat transfer method is popularly used in simulations and designs of internally cooled gas turbine blades. One of the important factors influencing its prediction accuracy is the choice of turbulence models for different fluid regions because the blade passage flow and internal cooling have considerably different flow features. However, most studies adopted the same turbulence models in passage flow and internal cooling. Another important issue is the comprehensive evaluation of the losses caused by flow and heat transfer for both fluid and solid regions. In this study, a RANS-based CHT solver for subsonic/transonic flows was developed based on OpenFOAM and validated and used to explore suitable RANS turbulence model combinations for internally cooled gas turbine blades. Entropy generation, able to weigh the losses caused by flow friction and heat transfer, was used in the analyses of two internally cooled vanes to reveal the loss mechanisms. Findings indicate that the combination of the k-? SST-?-Re? transition model for passage flow and the standard k-e model for internal cooling agreed best with measurement data. The relative error of vane dimensionless temperature was less than 3%. The variations of entropy generation with different internal cooling inlet velocities and temperatures indicate that reducing entropy generation was contradictory with enhancing heat transfer performance. This study, providing a reliable computing tool and a comprehensive performance parameter, has an important application value for the design of internally cooled gas turbine blades.

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.

Computational Modeling of Tip Heat Transfer to a Superscale Model of an Unshrouded Gas Turbine Blade

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Brian M. T. Tang ◽  
Pepe Palafox ◽  
Brian C. Y. Cheong ◽  
Martin L. G. Oldfield ◽  
David R. H. Gillespie
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Computational Study ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Tip Leakage Flow ◽  
Blade Tip

Control of over-tip leakage flow between turbine blade tips and the stationary shroud is one of the major challenges facing gas turbine designers today. The flow imposes large thermal loads on unshrouded high pressure (HP) turbine blades and is significantly detrimental to turbine blade life. This paper presents results from a computational study performed to investigate the detailed blade tip heat transfer on a sharp-edged, flat tip HP turbine blade. The tip gap is engine representative at 1.5% of the blade chord. Nusselt number distributions on the blade tip surface have been obtained from steady flow simulations and are compared with experimental data carried out in a superscale cascade, which allows detailed flow and heat transfer measurements in stationary and engine representative conditions. Fully structured, multiblock hexahedral meshes were used in the simulations performed in the commercial solver FLUENT. Seven industry-standard turbulence models and a number of different tip gridding strategies are compared, varying in complexity from the one-equation Spalart–Allmaras model to a seven-equation Reynolds stress model. Of the turbulence models examined, the standard k-ω model gave the closest agreement to the experimental data. The discrepancy in Nusselt number observed was just 5%. However, the size of the separation on the pressure side rim was underpredicted, causing the position of reattachment to occur too close to the edge. Other turbulence models tested typically underpredicted Nusselt numbers by around 35%, although locating the position of peak heat flux correctly. The effect of the blade to casing motion was also simulated successfully, qualitatively producing the same changes in secondary flow features as were previously observed experimentally, with associated changes in heat transfer with the blade tip.

Numerical Modelling Techniques for Turbine Blade Internal Cooling Passages

2015 ◽  
Author(s):  
Priyanka Dhopade ◽  
Luigi Capone ◽  
Matthew McGilvray ◽  
David Gillespie ◽  
Peter Ireland
Keyword(s):  
Heat Transfer ◽  
Numerical Modelling ◽  
Secondary Flow ◽  
Mesh Generation ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Modelling Techniques

Numerical modelling of internal cooling passages in gas turbine blades is a challenging task due to their physical characteristics, such as rounded duct corners, the presence of rib turbulators and their staggered locations between surfaces. This results in complex fluid dynamic phenomenon such as counter-rotating vortices and other secondary flow structures that can drive the heat transfer. Heat transfer mechanisms in such passages are inherently coupled with momentum transport and diffusion. Current industry practices for numerical modelling of such passages use unstructured mesh generation tools, steady Reynolds-averaged Navier-Stokes (RANS) equations and two-equation turbulence models such as k-ε and k-ω SST. This paper investigates two generic, engine-representative rib geometries using current numerical practices to determine their limitations. Three mesh generation tools and two turbulence models are compared across two rib geometries. The results are qualitatively and quantitatively compared to detailed experimental Nusselt numbers on the passage walls. It was found that as long as the rib geometry results in a secondary flow that directly impinges onto the wall, the meshing tools and turbulence models agree reasonably well with experiments. When the passage includes wall-wrapped ribs resulting in more complex secondary flows, this decreases the validity of the numerical tools, suggesting that more sophisticated modelling techniques are required as rib geometries continue to evolve.

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 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.

Influence of Channel Geometry and Flow Variables on Cyclone Cooling of Turbine Blades

2015 ◽  
Author(s):  
Martin Bruschewski ◽  
Christian Scherhag ◽  
Heinz-Peter Schiffer ◽  
Sven Grundmann
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Swirling Flow ◽  
Turbine Blades ◽  
Transfer Characteristic ◽  
Internal Cooling ◽  
Number Range ◽  
Flow Type ◽  
Magnetic Resonance Velocimetry ◽  
Swirl Generator

The presented study deals with the internal cooling of turbine blades by swirling flow. The sensitivity of this flow type is investigated towards Reynolds number, swirl intensity and the common geometric features of cooling ducts. The flow system consists of a straight and round channel that is attached to a tangential-type swirl generator. The channel outlet features various orifices and 180-degree-bends. The investigated Reynolds number range is Re = 2000…32000 and the geometric swirl numbers are S* = 1,3,5. The experiments were carried out with Magnetic Resonance Velocimetry for which water was used as flow medium. As the main outcome, it was found that the investigated flows are highly sensitive to the conditions at the outlet of the channel. But it was also discovered that for some channel outlets the flow field remains the same. The associated flow type features a favorable topology for heat transfer: The majority of mass is transported in the annular region close to the channel walls. Together with its high robustness, it is regarded as an applicable type for the internal cooling of turbine blades. A Large Eddy Simulation was conducted to analyze the heat transfer characteristic of this flow. For S*=3 and Re=20000, the simulation showed an averaged Nusselt number increase of factor 4.7 compared to fully-developed flow. However, a pressure loss increase of factor 43 must be considered as well. The presented measurements and simulations have led to a further understanding of swirling flows and proved these flows advantageous for the internal cooling of turbine blades.

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