Large-Eddy Simulations of Heat Transfer in a Ribbed Channel for Internal Cooling of Turbine Blades

2003 ◽  
Author(s):  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Square Channel ◽  
Nusselt Numbers ◽  
Separated Shear Layer ◽  
Friction Factors ◽  
Large Eddy

Large-Eddy Simulations (LES) are performed in a ribbed square channel with rib height to hydraulic diameter ratio of 0.1, and rib pitch to rib height ratio of 10. The calculations are performed for a nominal bulk Reynolds number of 20,000. Hydrodynamic and thermal fully-developed conditions are assumed. Results from two mesh resolutions, 963 and 1283 are presented and compared to available data in the literature. Time evolution, mean, and turbulent quantities are presented, together with the heat transfer. Both calculations capture the mean flow structures with precision and compare well with experimental data. Turbulent rms quantities also agree extremely well with available measurements. The finer mesh resolves the separated shear layer with greater precision and differences of 10–15% are observed between the two calculations. Similar differences are observed in the predictions of friction factors and Nusselt numbers between the two meshes. The friction factor and Nusselt number are underpredicted when compared to measurements in the literature.

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sunil Patil ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

scholarly journals 45° Staggered Rib Heat Transfer Coefficient Measurements in a Square Channel

1996 ◽  
Author(s):  
M. E. Taslim ◽  
A. Lengkong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors

For high blockage ribs with large heat transfer areas, commonly used in small gas turbine blades, the rib heat transfer is a significant portion of the overall heat transfer in the cooling passages. Three staggered 45° rib geometries corresponding to blockage ratios of 0.133, 0.167 and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5 and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface averaged heat transfer coefficients and friction factors for 45° ribs, and 90° ribs reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region were also compared. It was concluded that: a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. b) Except for two cases corresponding to the highest blockage ribs mounted at pitch-to-height ratios of 8.5 and 10 for which the heat transfer results of 45° ribs were very close to those of 90° ribs, 45° ribs produced higher heat transfer coefficients than 90° ribs. c) At pitch-to-height ratios of 8.5 and 10, all 45° ribs produced lower friction factors than 90° ribs. However, when they were brought closer to each other (S/e=5), they produced higher friction factors than 90° ribs. d) Heat transfer coefficients for the two smaller rib geometries (e/Dh=0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. f) Rib thermal performance decreased with the rib blockage ratio. For both angles of attack, the smallest rib geometry in the midstream position and at a pitch-to-height ratio of 10 had the highest thermal performance, and the highest blockage rib in the furthest upstream position produced the lowest thermal performance.

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.

scholarly journals Heat Transfer Potentiality and Flow Behavior in a Square Duct Fitted with Double-Inclined Baffles: A Numerical Analysis

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Amnart Boonloi ◽  
Withada Jedsadaratanachai
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Numerical Models ◽  
Flow Behavior ◽  
Square Duct ◽  
Square Channel ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Commercial Code ◽  
Volume Method

Numerical analysis of heat transfer mechanisms and flow topologies for the heat exchanger square channel (HESC) installed with the double-inclined baffles (DIB) is reported. The main objective of the present research is to study the influences of DIB height to duct height ( b / H = 0.05 – 0.30 ), DIB distance to duct height ( P / H = 1 – 1.5 ), and flow attack angle ( α = 30 °   and   45 ° ) on the flow topologies, heat transfer features, and thermal performances. The Reynolds numbers (based on the entry HESC around 100–2000) are analyzed for the present problem. The numerical models of the HESC installed with the DIB are solved with finite volume method (commercial code). The simulated results of the HESC installed with the DIB are reported in forms of flow topologies and heat transfer characteristics. The Nusselt numbers (Nu), friction factors ( f ), and thermal enhancement factors (TEF) of the HESC placed with the DIB are offered. As the numerical results, it is seen that the DIB produces the vortex streams and impinging streams in all cases. The vortex streams and impinging streams disturb the thermal boundary layer on the HESC walls that is a key motive for the growth of heat transfer rate. The best TEF of the HESC installed with the DIB is about 3.87 at P / H = 1 , α = 30 ° , Re = 2000 , and b / H = 0.15 . Additionally, the TEF contours, which help to design the HESC inserted with the DIB, are performed.

Large Eddy Simulation of the Developing Region of a Stationary Ribbed Internal Turbine Blade Cooling Channel

2004 ◽  
Author(s):  
Evan A. Sewall ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Turbine Blade ◽  
Internal Cooling ◽  
Mean Flow ◽  
Heat Transfer Augmentation ◽  
The Third ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Cooling Passage

This study reports on a Large Eddy Simulation (LES) of the entrance section of a gas turbine blade internal cooling passage. The channel is fitted with in-line turbulators orthogonal to the flow, and the domain studied covers the first six ribs of the channel. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.1, and the rib pitch-to-rib height ratio (P/e) is 10. A constant temperature boundary condition is imposed on the walls and the ribs, and the flow Reynolds number is 20,000. Results indicate that the mean flow is essentially fully developed by the fifth rib. Turbulent kinetic energy near the ribbed wall approaches fully developed values very quickly by the third or fourth ribs. However, turbulent intensities at the center of the duct are not fully developed by the sixth rib. As a consequence, heat transfer augmentation on the ribbed walls reaches a fully developed state quickly after the third rib, whereas, the smooth wall heat transfer augmentation shows a slight but steady increasing trend toward the fully developed value up to the sixth rib. Both augmentation ratios are to within 10% of their fully developed values after the third rib.

LES Simulation and Experimental Measurement of Fully Developed Ribbed Channel Flow and Heat Transfer

2002 ◽  
Author(s):  
Kazunori Watanabe ◽  
Toshihiko Takahashi
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Rotor Blade ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Ribbed Channel ◽  
Flow And Heat Transfer ◽  
Large Eddy

Ribbed channel flow is adopted for internal cooling of a 1300 °C class gas turbine first stage rotor blade. Heat transfer characteristics of transverse ribbed channel flow were examined using LES (Large Eddy Simulations) and by experiments. The flow was examined over the range of Reynolds number around 105 that are closer to the actual engine conditions. Computational results agreed reasonably well with experimental results. Heat transfer enhancement mechanism in a ribbed channel flow was shown to be caused by advecting eddy structure and interference of a rib.

RANS Evaluations of Internal Cooling Passage Geometries: Ribbed Passages and a 180 Degree Bend

2007 ◽  
Author(s):  
David Walker ◽  
Jack Zausner
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Moment Closure ◽  
Internal Cooling ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
New Formulation ◽  
Cooling Passage

A comprehensive study and assessment of RANS based turbulence models is performed on internal cooling duct passages of turbine blades. Conjugate computational heat transfer studies of 90 and 45 degree turbulated ducts are performed and compared to experimental data from the Von Karmon Institute. Spatially resolved Nusselt number distributions are computed using CFX in conjunction with several RANS based turbulence models. In addition, similar computational studies of a 180 degree turnaround bend are performed and compared to experimental data from Arizona State University. In that experiment, area averaged Nusselt numbers are provided at different locations throughout a 180 degree turn around bend. For both analyses, the experimental data sets are carefully chosen as the original authors/experimentalists clearly identified the geometry and boundary conditions such that there was no ambiguity for CFD analysis. For the 90 degree turbulator orientation, it was found that most two equation models largely under predicted heat transfer levels. For the 45 degree turbulator configuration, it was found that a new SST based turbulence formulation, provided by CFX, adequately matched the experimental data. For the 180 degree turnaround bend, Nusselt numbers were well predicted by this new formulation. For all geometries analyzed, resorting to a particular higher moment closure model inside of CFX provided no extra benefit in terms of accuracy.

45 deg Staggered Rib Heat Transfer Coefficient Measurements in a Square Channel

1998 ◽  
Vol 120 (3) ◽  
pp. 571-580 ◽  
Author(s):  
M. E. Taslim ◽  
A. Lengkong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors

For high-blockage ribs with large heat transfer areas, commonly used in small gas turbine blades, the rib heat transfer is a significant portion of the overall heat transfer in the cooling passages. Three staggered 45 deg rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface-averaged heat transfer coefficients and friction factors for 45 deg ribs, and 90 deg ribs reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. (b) Except for two cases corresponding to the highest blockage ribs mounted at pitch-to-height ratios of 8.5 and 10 for which the heat transfer results of 45 deg ribs were very close to those of 90 deg ribs, 45 deg ribs produced higher heat transfer coefficients than 90 deg ribs. (c) At pitch-to-height ratios of 8.5 and 10, all 45 deg ribs produced lower friction factors than 90 deg ribs. However, when they were brought closer to each other (S/e = 5), they produced higher friction factors than 90 deg ribs. (d) Heat transfer coefficients for the two smaller rib geometries (e/Dh = 0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. (e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. (f) Rib thermal performance decreased with the rib blockage ratio. For both angles of attack, the smallest rib geometry in the midstream position and at a pitch-to-height ratio of 10 had the highest thermal performance, and the highest blockage rib in the furthest upstream position produced the lowest thermal performance.

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