scholarly journals Partially-Covered Fractal Induced Turbulence On Fins Thermal Dissipation

2021 ◽  
Author(s):  
Soon Hong Chew ◽  
Su Min Hoi ◽  
Manh-Vu Tran ◽  
Ji Jinn Foo
Keyword(s):  
Heat Transfer ◽  
Power Spectra ◽  
Small Degree ◽  
Single Particle Tracking ◽  
Thermal Dissipation ◽  
Flow Fluctuations ◽  
Annulus Formation ◽  
Fluctuation Frequency ◽  
Turbulence Length ◽  
Turbulence Length Scale

Abstract The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh=22.0×103 were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique “Turbulence Annulus” formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. Furthermore, power spectra density unveiled the powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f=18.5Hz close to an optimal magnitude. Such intricate flow structures pave the way for superior thermal transfer capabilities, benefiting the community in developing for higher efficiency heat transfer systems.

The Effects of Freestream Turbulence, Turbulence Length Scale, and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitches of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at the exit Mach numbers of 0.55, 0.78, and 1.03, which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6×105, 8×105, and 11×105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared with the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

Darryl E. Metzger Memorial Session Paper: An Account of Free-Stream-Turbulence Length Scale on Laminar Heat Transfer

1995 ◽  
Vol 117 (3) ◽  
pp. 401-406 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Dominant Frequency ◽  
Length Scale ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Session Paper ◽  
Turbulence Length ◽  
Effective Intensity ◽  
Turbulence Length Scale

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed that accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter that accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

The Effects of Freestream Turbulence, Turbulence Length Scale and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2007 ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 105, 8 × 105, and 11 × 105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

Generalization of νt-92 Turbulence Model for Shear-Free and Stagnation Point Flows

2000 ◽  
Vol 123 (1) ◽  
pp. 11-15 ◽  
Author(s):  
A. N. Secundov ◽  
M. Kh. Strelets ◽  
A. K. Travin
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Transport Model ◽  
Turbulence Models ◽  
Length Scale ◽  
Stagnation Line ◽  
Flow And Heat Transfer ◽  
Turbulence Length ◽  
The One ◽  
Turbulence Length Scale

The one-equation, eddy-viscosity transport model of Gulyaev, Kozlov, and Secundov, νt-92, is modified and supplemented by an equation for the turbulence length scale. The advantages of the model developed here are demonstrated by computing a shear-free “boundary layer” on a flat plate, and the flow and heat transfer near the forward stagnation line of a circular cylinder. Both cases are known to be challenging for conventional turbulence models.

scholarly journals An Account of Free-Stream-Turbulence Length Scale on Laminar Heat Transfer

1994 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Dominant Frequency ◽  
Length Scale ◽  
Turbulence Parameter ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Turbulence Length ◽  
Effective Intensity ◽  
Turbulence Length Scale

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed which accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter which accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

Effect of Free-Stream Turbulence on Heat Transfer and Fluid Flow in a Transonic Turbine Stage

2006 ◽  
Author(s):  
F. Mumic ◽  
B. Sunden
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Turbulence Intensity ◽  
Rotational Speed ◽  
Free Stream ◽  
Length Scale ◽  
Turbine Stage ◽  
Free Stream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer.

Effects of Freestream Turbulence Intensity, Turbulence Length Scale, and Exit Reynolds Number on Vane Endwall Secondary Flow and Heat Transfer in a Transonic Turbine Cascade

2020 ◽  
Author(s):  
Zhigang Li ◽  
Bo Bai ◽  
Luxuan Liu ◽  
Jun Li ◽  
Shuo Mao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Turbulence Intensity ◽  
Thermal Load ◽  
Secondary Flows ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

Abstract In gas turbine engines, the first-stage vanes usually suffer harsh incoming flow conditions from the combustor with high pressure, high temperature and high turbulence. The combustor-generated high freestream turbulence and strong secondary flows in a gas turbine vane passage have been reported to augment the endwall thermal load significantly. This paper presents a detailed numerical study on the effects of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the endwall secondary flow pattern and heat transfer distribution of a transonic linear turbine vane passage at realistic engine Mach numbers, with a flat endwall no cooling. Numerical simulations were conducted at a range of different operation conditions: six freestream turbulence intensities (Tu = 1%, 5%, 10%, 13%, 16% and 20%), six turbulence length scales (normalized by the vane pitch of Λ/P = 0.01, 0.04, 0.07, 0.12, 0.24, 0.36), and three exit isentropic Mach number (Maex = 0.6, 0.85 and 1.02 corresponding exit Reynolds number Reex = 1.1 × 106, 1.7 × 106 and 2.2 × 106, respectively, based on the vane chord). Detailed comparisons were presented for endwall heat transfer coefficient distribution, endwall secondary flow field at different operation conditions, while paying special attention to the link between endwall thermal load patterns and the secondary flow structures. Results show that the freestream turbulence intensity and length scale have a significant influence on the endwall secondary flow field, but the influence of the exit Reynolds number is very weak. The Nusselt number patterns for the higher turbulence intensities (Tu = 16%, 20%) appear to be less affected by the endwall secondary flows than the lower turbulence cases. The thermal load distribution in the arc region around the vane leading edge and the banded region along the vane pressure side are influenced most strongly by the freestream turbulence intensity. In general, the higher freestream turbulence intensities make the vane endwall thermal load more uniform. The Nusselt number distribution is only weakly affected by the turbulence length scale when Λ/P is larger than 0.04. The heat transfer level appears to have a significant uniform augmentation over the whole endwall region with the increasing Maex. The endwall thermal load distribution is classified into four typical regions, and the effects of freestream turbulence, exit Reynolds number in each region were discussed in detail.

scholarly journals Measurements of the Effect of Free-Stream Turbulence Length Scale on Heat Transfer

1992 ◽  
Author(s):  
R. W. Moss ◽  
M. L. G. Oldfield
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Plate Boundary ◽  
Length Scale ◽  
Turbulence Scale ◽  
Free Stream Turbulence ◽  
High Turbulence ◽  
Gas Turbine Heat Transfer ◽  
Turbulence Length ◽  
Turbulence Length Scale

The effects of free-stream turbulence scale on heat transfer through a turbulent flat plate boundary layer have been measured. A variety of turbulence spectra were produced by parallel bar grids. The design of these was guided by previous measurements of combustion chamber turbulence. Heat transfer was measured transiently using thin film gauges. The heat transfer to the plate was found to be a function of turbulence integral length scale as well as intensity, and is of relevance to gas turbine heat transfer where aerofoils are subject to high turbulence levels from the combustor. Enhancement factors of up to 40% were experienced and the results extend conclusions drawn by other workers to higher turbulence levels and scales.

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