Rib Turbulator Heat Transfer Enhancements at Very High Reynolds Numbers

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Mingyang Zhang ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Geometrical Parameters ◽  
High Reynolds Numbers ◽  
Rib Turbulators ◽  
High Reynolds ◽  
Very High

High-pressure stage gas turbine blades feature serpentine passages where rib turbulators are installed to enhance heat transfer between the relatively colder air bled off from the compressor and the hot internal walls. Most of the prior studies have been restricted to Reynolds number of 90,000 and several studies have been carried out to determine geometrically optimized parameters for achieving high levels of heat transfer in this range of Reynolds number. However, for land-based power generation gas turbines, the Reynolds numbers are significantly high and vary between 105 and 106. The present study is targeted toward these high Reynolds numbers where traditional rib turbulator shapes and prescribed optimum geometrical parameters have been investigated experimentally. A steady-state liquid crystal thermography technique is employed for measurement of detailed heat transfer coefficient. Five different rib configurations, viz., 45 deg, V-shaped, inverse V-shaped, W-shaped, and M-shaped have been investigated for Reynolds numbers ranging from 150,000 to 400,000. The ribs were installed on two opposite walls of a straight duct with an aspect ratio of unity. For very high Reynolds numbers, the heat transfer enhancement levels for different rib shapes varied between 1.4 and 1.7 and the thermal hydraulic performance was found to be less than unity.

Temperature Control of Blow-Down, Supersonic Tunnels

1956 ◽  
Vol 60 (541) ◽  
pp. 67-70
Author(s):  
T. A. Thomson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Stagnation Temperature ◽  
Blow Down ◽  
High Reynolds Numbers ◽  
Experimental Errors ◽  
High Reynolds

The blow-down type of intermittent, supersonic tunnel is attractive because of its simplicity and because relatively high Reynolds numbers can be obtained for a given size of test section. An adverse characteristic, however, is the fall of stagnation temperature during runs, which can affect experiments in several ways. The Reynolds number varies and the absolute velocity is not constant, even if the Mach number and pressure are; heat-transfer cannot be studied under controlled conditions and the experimental errors arising from the effect of heat-transfer on the boundary layer vary in time. These effects can become significant in quantitative experiments if the tunnel is large and the variation of temperature very rapid; the expense required to eliminate them might then be justified.

Heat Transfer Coefficient Distribution of W and Broken W Turbulators At High Reynolds Numbers

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Étienne Robert ◽  
Peter Ireland
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
Smooth Channel ◽  
Wide Range ◽  
High Reynolds

Abstract An experimental and numerical study of the convective heat transfer enhancement provided by two rib families (W and Broken W) is presented, covering Reynolds numbers (Re) between 300,000 to 900,000 in a straight channel with a rectangular cross section (AR=1.29). These high Reynolds numbers were selected for the current study since most data in the available literature typically pertain to investigations at lower Reynolds numbers. The objective of this study is to assess the local heat transfer coefficient (HTC) enhancement (compared with a smooth channel) and the overall thermal performance, taking into account the effect of increased roughness on the friction factor, of a group of W shaped turbulators over a wide range of Reynolds numbers. Furthermore, the effects of increasing the rib spacing on the thermal performance of the Broken W configuration are presented and discussed. The numerical results are compared against heat transfer measurements obtained using the Transient Liquid Crystal (TLC) method. The research shows that for the Broken W turbulators, increasing the Reynolds number is associated with an overall decrease of the thermal performance while the thermal performance of the W configuration is relatively insensitive to Reynolds number. Nevertheless, the Broken W configuration delivers higher thermal performance and heat transfer compared with the W configuration for the range of Re investigated. The Broken W configuration with a pitch spacing of 10 times the rib height was shown to provide the optimal thermal performance in the configurations investigated here.

Turbulent boundary layer statistics at very high Reynolds number

2015 ◽  
Vol 779 ◽  
pp. 371-389 ◽  
Author(s):  
M. Vallikivi ◽  
M. Hultmark ◽  
A. J. Smits
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Mean Velocity ◽  
High Reynolds Numbers ◽  
Layer Flow ◽  
High Reynolds ◽  
Very High

Measurements are presented in zero-pressure-gradient, flat-plate, turbulent boundary layers for Reynolds numbers ranging from $\mathit{Re}_{{\it\tau}}=2600$ to $\mathit{Re}_{{\it\tau}}=72\,500$ ($\mathit{Re}_{{\it\theta}}=8400{-}235\,000$). The wind tunnel facility uses pressurized air as the working fluid, and in combination with MEMS-based sensors to resolve the small scales of motion allows for a unique investigation of boundary layer flow at very high Reynolds numbers. The data include mean velocities, streamwise turbulence variances, and moments up to 10th order. The results are compared to previously reported high Reynolds number pipe flow data. For $\mathit{Re}_{{\it\tau}}\geqslant 20\,000$, both flows display a logarithmic region in the profiles of the mean velocity and all even moments, suggesting the emergence of a universal behaviour in the statistics at these high Reynolds numbers.

Heat Transfer and Pressure Drop Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Nawaf Y. Alkhamis ◽  
Akhilesh P. Rallabandi ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Rib Roughened

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+).

scholarly journals Extreme dissipation and intermittency in turbulence at very high Reynolds numbers

2020 ◽  
Vol 476 (2243) ◽  
pp. 20200591
Author(s):  
Gerrit E. Elsinga ◽  
Takashi Ishihara ◽  
Julian C. R. Hunt
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Small Scale ◽  
Scaling Exponent ◽  
High Reynolds Numbers ◽  
Layer Structures ◽  
High Reynolds ◽  
Very High

Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.

Heat Transfer and Pressure Losses of W-Shaped Small Ribs at High Reynolds Numbers for Combustor Liner

2010 ◽  
Author(s):  
Tomoko Hagari ◽  
Katsuhiko Ishida ◽  
Takeo Oda ◽  
Yasushi Douura ◽  
Yasuhiro Kinoshita
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Cooling Passage ◽  
Combustor Liner ◽  
Rib Roughened

The present study investigates the heat transfer performance of W-shaped ribs in a rectangular channel with typical geometries and flow conditions for a combustor liner cooling passage. In order to assess the Reynolds number dependence on heat transfer enhancement by the ribs for the combustor cooling passage, experiments were conducted with channel Reynolds number ranging from 40,000 to 550,000. The ribs were located on one side of the channel and the rib height-to-hydraulic diameter ratio (e/Dh) was 0.006 to 0.014, which simulate the combustor liner cooling configurations. Rib pitch-to-height ratio (P/e) was 10. Rib-roughened copper plates with constant temperature were used to measure the averaged heat transfer coefficients. Measured results show that the heat transfer enhancements of about 3 were obtained over that of a flat plate at high Reynolds numbers for all cases. The slope of heat transfer coefficient becomes constant with increasing Reynolds number because of the laminar-turbulent transition around the ribs, which is considered to occur at Reynolds number based on rib height of about 1,000. Pressure loss measurements showed that the friction coefficients are constantly 3–4.5 times higher than those of a flat plate for a fully turbulent flow such as a combustor cooling passage. Pressure loss by ribs seems not to have a significant impact to the overall combustor performance. Numerical calculations were conducted additionally for all test cases. Predicted amount of heat released from the ribs contributes about 40% of overall heat release even for low ribs. Heat transfer on the rib surface is essential in the evaluation of the rib-roughened cooling passage.

Heat Transfer and Pressure Losses of W-Shaped Small Ribs at High Reynolds Numbers for Combustor Liner

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Tomoko Hagari ◽  
Katsuhiko Ishida ◽  
Takeo Oda ◽  
Yasushi Douura ◽  
Yasuhiro Kinoshita
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Cooling Passage ◽  
Combustor Liner ◽  
Rib Roughened

The present study investigates the heat transfer performance of W-shaped ribs in a rectangular channel with typical geometries and flow conditions for a combustor liner cooling passage. In order to assess the Reynolds number dependence on heat transfer enhancement by the ribs for the combustor cooling passage, experiments were conducted with channel Reynolds number ranging from 40,000 to 550,000. The ribs were located on one side of the channel and the rib height-to-hydraulic diameter ratio (e/Dh) was 0.006–0.014, which simulate the combustor liner cooling configurations. Rib pitch-to-height ratio (P/e) was 10. Rib-roughened copper plates with constant temperature were used to measure the averaged heat transfer coefficients. Measured results show that the heat transfer enhancements of about 3 were obtained over that of a flat plate at high Reynolds numbers for all cases. The slope of heat transfer coefficient becomes constant with increasing Reynolds number because of the laminar-turbulent transition around the ribs, which is considered to occur at Reynolds number based on rib height of about 1000. Pressure loss measurements showed that the friction coefficients are constantly 3–4.5 times higher than those of a flat plate for a fully turbulent flow such as a combustor cooling passage. Pressure loss by ribs seems not to have a significant impact to the overall combustor performance. Numerical calculations were conducted additionally for all test cases. Predicted amount of heat released from the ribs contributes about 40% of the overall heat release even for low ribs. Heat transfer on the rib surface is essential in the evaluation of the rib-roughened cooling passage.

An Experimental Study of the Friction Factor and Mass Transfer Performance of an Offset-Strip Fin Array at Very High Reynolds Numbers

2007 ◽  
Vol 129 (9) ◽  
pp. 1134-1140 ◽  
Author(s):  
Gregory J. Michna ◽  
Anthony M. Jacobi ◽  
Rodney L. Burton
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Reynolds Numbers ◽  
Transfer Performance ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Offset Strip Fin ◽  
Very High

Thermal-hydraulic performance data for offset-strip fin arrays are readily available in the range Re<10,000. However, in emerging applications in automotive and aerospace systems, where fan power is not a constraint and compactness is important, it may be desirable to operate offset-strip fin heat exchangers at very high Reynolds numbers. In this paper, friction factor and mass transfer performance of an offset-strip fin array at Reynolds numbers between 10,000 and 120,000 are characterized. A scale-model, eight-column fin array is used in pressure drop and naphthalene sublimation experiments, and the data are compared to predictions of performance given by available analytical models and extrapolations of the best available correlations. The friction factor data follow the correlation-predicted trend of decreasing monotonically as the Reynolds number is increased to 20,000. However, at higher Reynolds numbers, the friction factor increases as the Reynolds number increases and local maxima are observed in the data. Over the range investigated, the modified Colburn j factor decreases monotonically as the Reynolds number increases. For Reynolds numbers in the range 10,000<Re<120,000, well beyond that covered by state-of-the-art correlations, both the friction factor and Colburn j factor are roughly twice that predicted by extrapolating the best available correlations. The higher-than-predicted Colburn j factor at very high Reynolds numbers is encouraging for the use of offset-strip fin heat exchangers in emerging applications where compactness is of high importance.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 375-385 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]

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