Comparison of Turbulence Models With Experiment for Heat Transfer in a Cooling Channel With Dimples

2010 ◽  
Author(s):  
Krishna Guntur ◽  
R. S. Amano ◽  
Jose Martinez Lucci
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Turbulence Models ◽  
Cooling Channel ◽  
Numerical Computations ◽  
Turbine Blade Cooling ◽  
Blade Cooling ◽  
Heat Transfer Efficiency ◽  
Smooth Channel ◽  
Recent Developments

Turbine blade cooling is one of the most important developments in gas turbine history. Development of blade cooling enabled increase in firing temperature and in turn improving the efficiency. Different cooling channel geometries have been tested for improving the heat transfer efficiency. Smooth channels, channels with sharp bends, channels with ribs and other such tabulators were used to improve the turbulence and thereby increasing the efficiency. In the recent developments, hemi-spherical dimples are being considered instead of ribs as dimples have less pressure loss. This paper compares numerical computations of the heat transfer characteristics of a dimpled rectangular channel with published experimental values. Reynolds number ranges from 5000 to 40,000. For the numerical computations two different turbulence models, k-ε and k-ω models are used, the software for the simulation was Fluent and grid generation was achieved by Ansys workbench. The dimpled channel results are normalized with the smooth channel results.

Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Kai-Chieh Chia ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Cooling Channel ◽  
Rotation Direction ◽  
Smooth Channel ◽  
Blade Tip ◽  
The Impact ◽  
Turn Region

Abstract The tip turn region within the gas turbine blade experienced severe thermal issues related to temperature variations and temperature gradients. The current study experimentally measured the heat transfer distribution of the internal blade tip wall in a rotating cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180 deg turn, complex three-dimensional flow significantly affected the heat transfer on the internal tip surface. The steady-state liquid crystal method was used to obtain a detailed distribution of heat transfer on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45 deg angled ribs. The Reynolds number inside the pressurized cooling channel ranged from 10,000 to 30,000, and the rotation number was up to 0.53. Furthermore, two-channel orientations (90 deg and 135 deg) with respect to the rotation direction were tested. The tip heat transfer from the smooth channel wall was more sensitive to rotation, and the largest heat transfer enhancement caused by rotation was 68%. Channel orientation of 90 deg produced higher heat transfer compared to the orientation of 135 deg.

Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

2019 ◽  
Author(s):  
Kai-Chieh Chia ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Three Dimensional Flow ◽  
Smooth Channel ◽  
Blade Tip ◽  
The Impact

Abstract The current study experimentally studied heat transfer characteristics of the blade tip wall in a rotating internal cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180° turn, complex three dimensional flow significantly affected heat transfer on the internal tip surface. The liquid crystal method is used to capture the heat transfer contour on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45° angled ribs. The Reynolds number inside the pressurize two-pass cooling channel ranged from 10,000 to 30,000 at both stationary and rotating conditions. Furthermore, two channel orientations (90° and 135°) were tested. The effect of Coriolis force on heat transfer is studied with the rotation number up to 0.53. The tip heat transfer from the smooth channel wall was more sensitive to rotation and the largest heat transfer enhancement as a result of rotation was 68%.

scholarly journals Validation of Flow Field and Heat Transfer in a Two-Pass Internal Cooling Channel Using Different Turbulence Models

2013 ◽  
Author(s):  
Federica Farisco ◽  
Stefan Rochhausen ◽  
Metin Korkmaz ◽  
Michael Schroll
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Field ◽  
Cooling System ◽  
Flow Direction ◽  
Turbulence Models ◽  
Flow Structures ◽  
Cooling Channel ◽  
Test Bed ◽  
Smooth Channel

In this work the flow regime within a generic turbine cooling system is investigated numerically. The main objective is to validate the performance of various turbulence models with different complexity by comparing the numerical results with experimental data. To maximize surface heat transfer rates, present-day cooling systems of high pressure turbines have highly complex shapes generating high turbulence levels and flow separations. These flow structures lead to higher requirements of CFD-techniques for sufficient prediction. To simulate complex flows in the industrial design process, Reynolds averaged Navier-Stokes (RANS) techniques are applied instead of computationally expensive LES and DNS simulations. Therefore, higher order turbulence models are necessary to predict flow field and heat transfer performance in such complex motion. The DLR standard flow solver for turbomachinery flows, TRACE, is used to solve the RANS equations. Four turbulence models have been analysed: the one equation model of Spalart and Allmaras, the two equation k – ω model of Wilcox, the two equation k – ω SST model of Menter and the anisotropy resolving Explicit Algebraic Reynolds Stress model (EARSM) of Hellsten. The investigated cooling geometry consists of a two-pass smooth channel with a 180 degree bend. At the DLR institute of propulsion technology PIV measurements in a rotating cooling channel test bed for Rotation numbers up to 0.1 have been performed. This work uses the experimental data for Re = 50,000 and Ro = 0 without rotation for comparison. For all models adiabatic and diabatic calculations have been performed. In order to accurately apply the turbulence models, a study concerning the turbulent boundary conditions has been performed prior to the calculations. The results obtained through RANS simulations are presented in comparison with the experiments along planes in the flow direction and in the orthogonal direction to study the velocity field, the shape and size of the separation bubbles and the wall shear stress. The EARSM predicts the flow field overall more accurately with improved agreement between all relevant parameters compared to the other models. The diabatic simulations reflect the adiabatic results. However, it can be noticed that higher complexity in turbulence modelling is related to increased heat transfer. Our work confirms the EARSMs ability to predict complex flow structures better than the more elementary approaches.

Effects of the Location of the Pocket Cavity on Heat Transfer and Flow Characteristics of the Endwall With a Symmetrical Vane

2018 ◽  
Author(s):  
Jian Liu ◽  
Safeer Hussain ◽  
Lei Wang ◽  
Gongnan Xie ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Guide Vane ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Boundary Edge ◽  
Head Region ◽  
High Heat Transfer ◽  
Smooth Channel

A pocket cavity is generated at the junction position of the Low Pressure Turbine (LPT) and the Outlet Guide Vane (OGV) in the rear part of a gas turbine engine. The OGV mainly controls the exhaust flow exiting and provides structural strength of the main engine frame. In the present work, the effect the location of the pocket on the heat transfer of the endwall with a symmetrical vane is investigated. A triangular pocket cavity is built in a rectangular channel and a symmetric vane is put on the endwall downstream of the pocket cavity. Heat transfer and turbulent flow characteristics over the endwall are investigated experimentally and numerically. The distance between the pocket cavity and the symmetrical vane is varied from 10 cm, 15 cm, and 20 cm. Liquid Crystal Thermography (LCT) is employed to measure the heat transfer over the endwall at Reynolds number ranging from 87,600 to 219,000. The turbulent flow details are presented by numerical calculations with the turbulence models, i.e., the k-ω SST model. From this study, high heat transfer regions are usually found at where flow impingement appears, i.e., the pocket boundary edge region and the vane head region. Compared with the case of the smooth channel, the heat transfer is decreased when a pocket cavity is placed upstream of the vane. With the distance between the pocket cavity and the vane becoming larger, the effect of the pocket cavity is weakened and the heat transfer is approaching the smooth channel case, i.e., case 0. The pocket cavity strengthens the flow shedding and separates the flow away from the endwall. The pushed upward flow weakens the flow impingement on the vane and then leads to the decreased heat transfer around the vane.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Spatially Resolved Heat Transfer and Friction Factors in a Rectangular Channel With 45-Deg Angled Crossed-Rib Turbulators

2003 ◽  
Vol 125 (3) ◽  
pp. 575-584 ◽  
Author(s):  
P. M. Ligrani ◽  
G. I. Mahmood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Test Surface ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially resolved Nusselt numbers, spatially averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with perpendicular orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 10,000 to 83,700. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25% of the channel cross-sectional area. Nusselt numbers are given both with and without three-dimensional conduction considered within the acrylic test surface. In both cases, spatially resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer reattachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) vary locally on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. When adjusted to account for conduction along and within the test surface, Nusselt number ratios show different quantitative variations (with location along the test surface), compared to variations when no conduction is included. Changes include: (i) decreased local Nusselt number ratios along the central part of each rib top surface as heat transfer from the sides of each rib becomes larger, and (ii) Nusselt number ratio decreases near corners, where each rib joins the flat part of the test surface, especially on the downstream side of each rib. With no conduction along and within the test surface (and variable heat flux assumed into the air stream), globally-averaged Nusselt number ratios vary from 2.92 to 1.64 as Reynolds number increases from 10,000 to 83,700. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range, with values in approximate agreement with data measured by other investigators in a square channel also with 45 deg oriented ribs.

Flow in a Simulated Turbine Blade Cooling Channel With Spatially Varying Roughness Caused by Additive Manufacturing Orientation

2021 ◽  
Author(s):  
Stephen T. McClain ◽  
David R. Hanson ◽  
Emily Cinnamon ◽  
Robert Kunz ◽  
Jacob C. Snyder ◽  
...  
Keyword(s):  
Additive Manufacturing ◽  
Turbine Blade ◽  
Cooling Channel ◽  
Turbine Blade Cooling ◽  
Blade Cooling ◽  
Spatially Varying
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