Using turbulent Prandtl number and transition models to improve the prediction of turbine blade heat transfer coefficients

1992 ◽  
Author(s):  
KEVIN WHITAKER
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Turbine Blade ◽  
Turbulent Prandtl Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transition Models

Prediction of Jet Impingement Heat Transfer Using a Hybrid Wall Treatment With Different Turbulent Prandtl Number Functions

1996 ◽  
Vol 118 (3) ◽  
pp. 562-569 ◽  
Author(s):  
G. K. Morris ◽  
S. V. Garimella ◽  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Prandtl Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Maximum Deviation ◽  
Turbulent Prandtl Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Numerical Predictions

The local heat transfer coefficient distribution on a square heat source due to a normally impinging, axisymmetric, confined, and submerged liquid jet was computationally investigated. Numerical predictions were made for nozzle diameters of 3.18 and 6.35 mm at several nozzle-to-heat source spacings, with turbulent jet Reynolds numbers ranging from 8500 to 13,000. The commercial finite-volume code FLUENT was used to solve the thermal and flow fields using the standard high-Reynolds number k–ε turbulence model. The converged solution obtained from the code was refined using a post-processing program that incorporated several near-wall models. The role of four alternative turbulent Prandtl number functions on the predicted heat transfer coefficients was investigated. The predicted heat transfer coefficients were compared with previously obtained experimental measurements. The predicted stagnation and average heat transfer coefficients agree with experiments to within a maximum deviation of 16 and 20 percent, respectively. Reasons for the differences between the predicted and measured heat transfer coefficients are discussed.

Effect of Turbulent Prandtl Number on Convective Heat Transfer to Turbulent Flow of a Supercritical Fluid in a Vertical Round Tube

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Mahdi Mohseni ◽  
Majid Bazargan
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Supercritical Fluid ◽  
Turbulence Model ◽  
Energy Transport ◽  
Viscous Sublayer ◽  
Turbulent Prandtl Number ◽  
Transfer Coefficients ◽  
Round Tube ◽  
Heat Transfer Coefficients

A two-dimensional numerical model is developed to study the effect of the turbulent Prandtl number Prt on momentum and energy transport in a highly variable property flow of supercritical fluids in a vertical round tube. Both regimes of enhanced and deteriorated heat transfer have been investigated. The equations of the Prt leading to the best agreement with the experiments in either regime of heat transfer were specified. The results of this study show that the increase in the Prt causes the heat transfer coefficients to decrease. When the buoyancy force increases, a better agreement with the experimental data is reached if values lower than 0.9 are used for the Prt. A decrease in the Prt values results in an increase in turbulent activities. From the effect that the Prt has on heat transfer coefficients, it may be deduced that the buoyancy effects in the upward flow of a supercritical fluid lead to the decrease in the Prt value and hence to the increase in the heat transfer coefficients. Furthermore, the value of the Prt in the laminar viscous sublayer as expected does not have a significant effect on heat transfer rate. The effect of the turbulence model on the extent to which the Prt influences the rate of heat transfer is also examined. The results obtained are shown to be valid regardless of the turbulence model used.

Effect of Turbulent Prandtl Number on Convective Heat Transfer to Turbulent Upflow of Supercritical Carbon Dioxide

2009 ◽  
Author(s):  
Majid Bazargan ◽  
Mahdi Mohseni
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Turbulent Prandtl Number ◽  
Upward Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Supercritical Carbon

A two-dimensional model is developed to simultaneously solve the momentum and energy equations and thus predict convection heat transfer to an upward flow of supercritical carbon dioxide in a round tube. The effect of the turbulent Prandtl number, Prt, on heat transfer coefficients has been extensively studied. A number of constant values of Prt, as well as a number of suggested equations accounting for variations of Prt with flow conditions, have been examined. The investigation has been carried out for both regimes of enhanced and deteriorated heat transfer. The results of this study show that the increase of Prt, even in the viscous sublayer, cause the heat transfer coefficients to decrease. The models of Prt leading to best agreement with experiments in either regimes of heat transfer were recognized. From the effect Prt has on heat transfer coefficients, it has been deduced that the buoyancy effects in upward flow of a supercritical fluid causes the Prt to decrease and hence the heat transfer coefficients to increase.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade

2003 ◽  
Vol 125 (4) ◽  
pp. 648-657 ◽  
Author(s):  
Jae Su Kwak ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Rotor Blade ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. The Reynolds number based on cascade exit velocity and axial chord length was 1.1×106 and the total turning angle of the blade was 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.

scholarly journals Effect of Discrete Ribs on Heat Transfer and Friction Inside Narrow Rectangular Cross Section Cooling Passage of Gas Turbine Blade

2021 ◽  
Vol 10 (6) ◽  
pp. 192-209
Author(s):  
Karthik Krishnaswamy ◽  
◽  
Srikanth Salyan ◽  
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cooling Passage

The performance of a gas turbine during the service life can be enhanced by cooling the turbine blades efficiently. The objective of this study is to achieve high thermohydraulic performance (THP) inside a cooling passage of a turbine blade having aspect ratio (AR) 1:5 by using discrete W and V-shaped ribs. Hydraulic diameter (Dh) of the cooling passage is 50 mm. Ribs are positioned facing downstream with angle-of-attack (α) of 30° and 45° for discrete W-ribs and discerte V-ribs respectively. The rib profiles with rib height to hydraulic diameter ratio (e/Dh) or blockage ratio 0.06 and pitch (P) 36 mm are tested for Reynolds number (Re) range 30000-75000. Analysis reveals that, area averaged Nusselt numbers of the rib profiles are comparable, with maximum difference of 6% at Re 30000, which is within the limits of uncertainty. Variation of local heat transfer coefficients along the stream exhibited a saw tooth profile, with discrete W-ribs exhibiting higher variations. Along spanwise direction, discrete V-ribs showed larger variations. Maximum variation in local heat transfer coefficients is estimated to be 25%. For experimented Re range, friction loss for discrete W-ribs is higher than discrete-V ribs. Rib profiles exhibited superior heat transfer capabilities. The best Nu/Nuo achieved for discrete Vribs is 3.4 and discrete W-ribs is 3.6. In view of superior heat transfer capabilities, ribs can be deployed in cooling passages near the leading edge, where the temperatures are very high. The best THPo achieved is 3.2 for discrete V-ribs and 3 for discrete W-ribs at Re 30000. The ribs can also enhance the power-toweight ratio as they can produce high thermohydraulic performances for low blockage ratios.

Unsteady Wake Effect on Film Effectiveness and Heat Transfer Coefficient From a Turbine Blade With One Row of Air and CO2 Film Injection

1994 ◽  
Vol 116 (4) ◽  
pp. 921-928 ◽  
Author(s):  
S. Ou ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Strouhal Number ◽  
Turbine Blade ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Wake Effect ◽  
Pressure Surface ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake

The effect of unsteady wake and film injection on heat transfer coefficients and film effectiveness from a gas turbine blade was found experimentally. A spoked wheel type wake generator produced the unsteady flow. Experiments were done with a five airfoil linear cascades in a low-speed wind tunnel at a chord Reynolds number of 3 × 105, two wake Strouhal numbers of 0.1 and 0.3, and a no-wake case. A model turbine blade injected air or CO2 through one row of film holes each on the pressure and suction surfaces. The results show that the large-density injectant (CO2) causes higher heat transfer coefficients on the suction surface and lower heat transfer coefficients on the pressure surface. At the higher blowing ratios of 1.0 and 1.5, the film effectiveness increases with increasing injectant-to-mainstream density ratio at a given Strouhal number. However, the density ratio effect on film effectiveness is reversed at the lowest blowing ratio of 0.5. Higher wake Strouhal numbers enhance the heat transfer coefficients but reduce film effectiveness for both density ratio injectants at all three blowing ratios. The effect of the wake Strouhal number on the heat transfer coefficients on the suction surface is greater than that on the pressure surface.

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