Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

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.

Heat Transfer Enhancement of Reactor Utilizing Taylor-Poiseuille Flow

2014 ◽  
Author(s):  
Li Ye ◽  
Huajun Peng ◽  
Bo Zhou ◽  
Mo Yang ◽  
Zheng Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Regime ◽  
Poiseuille Flow ◽  
Axial Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Taylor Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Numerical studies have been conducted to determine the heat transfer performances in a Taylor-Poiseuille flow regime. The flow is confined between two different heated, concentric cylinders. The inner cylinder is allowed to rotate while the outer one remains fixed, an axial flow is added. The influences of rotation Taylor number and axial Reynolds number on heat transfer coefficients are investigated. Results show that temperature in the flow regime presents a remarkable sinusoidal periodicity as the result of the axial arrangement of Taylor vortices, so does the local heat transfer coefficients. Heat transfer efficiency gets strengthened with increasing Taylor number, while damped with increasing Reynolds number. The accuracy of the simulation is validated by compared to the existing linear stability analysis.

Computational and Experimental Studies of Midpassage Gap Leakage and Misalignment for a Non-Axisymmetric Contoured Turbine Blade Endwall

2016 ◽  
Author(s):  
Eric Lange ◽  
Stephen Lynch ◽  
Scott Lewis
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Computational Study ◽  
Experimental Studies ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Recirculation Region ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Turbine vanes and blades are generally manufactured as single or double airfoil sections that must each be installed onto a turbine disk. Between each section, a gap at the endwalls through the blade passage is present, through which high pressure coolant is leaked. Furthermore, sections can become misaligned due to thermal expansion or centrifugal forces. Flow and heat transfer around the gap is complicated due to the interaction of the mainstream and the leakage flow. An experimental and computational study was undertaken to determine the physics of the leakage flow interaction for a realistic turbine blade endwall, and assess whether steady RANS CFD, commonly used for non-axisymmetric endwall design, can be used to accurately model this interaction. Computational models were compared against experimental observations of endwall heat transfer on a contoured endwall with a midpassage gap. Endwall heat transfer coefficients were determined experimentally by using infrared thermography to capture spatially-resolved surface temperatures on a uniform heat flux surface (heater) attached to the endwall. Predictions and measurements both indicated an increase in endwall heat transfer with increasing gap leakage flow, although the distribution of heat transfer coefficients along the gap was not well captured by CFD. A misalignment of the blade endwall causing a forward-facing step for the near-endwall flow resulted in a large highly turbulent recirculation region downstream of the step and high local heat transfer that was overpredicted by CFD. Conversely, a backward-facing step reduced turbulence and local heat transfer. The misprediction of local heat transfer around the gap is thought to be caused by unsteady interaction of the passage secondary flow and gap leakage flow, which cannot be well-captured by a steady RANS approach.

Heat Transfer to an Airfoil in Oscillating Flow

1971 ◽  
Vol 93 (4) ◽  
pp. 461-468 ◽  
Author(s):  
J. A. Miller ◽  
P. F. Pucci
Keyword(s):  
Heat Transfer ◽  
Oscillation Frequency ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Oscillating Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Consequent Increase

Local heat transfer coefficients to an airfoil in an oscillating stream have been measured for a range of frequencies and oscillation amplitudes. Results at moderate angles of attack are in agreement with previously reported findings. However, at large angles of attack, including those associated with stall in steady flow, a strong periodic starting vortex shed from the leading edge leads to a dramatic reattachment of the flow and consequent increase in local Nusselt Numbers of as much as five-fold. These effects are shown to be amplified by increasing oscillation frequency and amplitude.

Effects of Reynolds Number and Pressure Ratio on Leakage Loss and Heat Transfer in a Stepped Labyrinth Seal

2001 ◽  
Author(s):  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Operating Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Sealing Performance

The influence of Reynolds number and pressure ratio on the operating characteristics of a stepped labyrinth seal was experimentally determined. The geometries investigated represent designs of a stepped labyrinth seal typical for modern jet engines. Heat transfer and discharge measurements were obtained for two plane models with various seal clearances. The experiments covered a range of Reynolds numbers and pressure ratios. Independent variation of Reynolds number and pressure ratio was obtained by adjusting the back pressure at the seal exit for a given pressure ratio. Dimensionless discharge coefficients, describing the sealing performance, were derived from the measured leakage rates. Pressure ratio, Reynolds number, tip geometry and seal clearance all affected the sealing performance. Finite element calculations were employed to calculate the local heat transfer coefficients from the measured wall and gas temperatures. Averaging of the local values yielded mean heat transfer coefficients and mean Nusselt numbers. The heat transfer was mainly determined by the Reynolds number. Compressibility effects on the heat transfer were observed to be very small.

Local Heat Transfer in Enclosed Co-rotating Disks With Axial Throughflow

1994 ◽  
Vol 116 (1) ◽  
pp. 66-72 ◽  
Author(s):  
S. Y. Kim ◽  
J. C. Han ◽  
G. L. Morrison ◽  
E. Elovic
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Axial Flow ◽  
Local Heat Transfer ◽  
Disk Surface ◽  
Local Heat ◽  
Outer Radius ◽  
Rotating Disks ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Local heat transfer in enclosed co-rotating disks with axial through flow is investigated. The rotating cavity has two plane disks and a cylindrical rim (shroud). The ratio of the rim span to the disk outer radius is 0.4 and the ratio of the disk inner radius to outer radius is 0.25. The objectives of this study are to investigate the effects of axial coolant flow rate, rotation speed, and disk surface temperature on the local heat transfer coefficients inside the disk cavity. Both uniform disk surface heat flux and uniform disk surface temperatures are tested for axial flow Reynolds numbers between 2500 and 25,000 rotational Reynolds numbers between 0 and 5.11 × 105, and rotational Grashof numbers between 5 × 106 and 1.3 × 1010. The results show that the local heat transfer coefficients for the nonrotating cavity increase with increasing axial flow Reynolds number. In general, the local Nusselt numbers at large radii of the disks and rim increase with increasing rotational Reynolds number. However, the local Nusselt numbers at small radii of the disks initially decrease and then increase with increasing rotational Reynolds number. The uniform heat flux condition provides slightly higher heat transfer coefficients than those for the uniform wall temperature condition.

Heat Transfer in the Oscillating Turbulent Boundary Layer

1969 ◽  
Vol 91 (4) ◽  
pp. 239-244 ◽  
Author(s):  
James A. Miller
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Local Coefficients

Measurements of local heat-transfer coefficients in the fully established oscillating turbulent boundary layer over a flat plate are reported. In the range of frequencies from 0.1 to 200 cps and amplitudes from 8 to 92 percent of the freestream mean velocity, increases in local Nusselt numbers of 3 to 5 percent were found. It is concluded that substantial increases in local coefficients, sometimes reported in oscillating flows of low standing wave ratio, may be traced to reduced transition Reynolds numbers.

scholarly journals Heat Transfer in the Oscillating Turbulent Boundary Layer

1969 ◽  
Author(s):  
J. A. Miller
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Local Coefficients

Measurements of local heat transfer coefficients in the fully established oscillating turbulent boundary layer over a flat plate are reported. In the range of frequencies from 0.1 to 200 cps and amplitudes from 8 to 92 percent of the freestream mean velocity increases in local Nusselt numbers of 3 to 5 percent were found. It is concluded that substantial increases in local coefficients sometimes reported in oscillating flows of low standing wave ratio may be traced to reduced transition Reynolds numbers.

Effect of Squealer Cavity Depth and Oxidation on Turbine Blade Tip Heat Transfer

2001 ◽  
Author(s):  
Ronald S. Bunker ◽  
Jeremy C. Bailey
Keyword(s):  
Heat Transfer ◽  
Mach Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Blade Cascade ◽  
Blade Tip

An experimental study has been performed to investigate the effect of squealer cavity depth on the detailed distribution of convective heat transfer coefficients of a turbine blade tip surface. This paper presents full surface information on heat transfer coefficients within a blade cascade which develops an appropriate pressure distribution about an airfoil blade tip and shroud model. A stationary blade cascade experiment has been run consisting of three airfoils, the center airfoil having a variable tip gap clearance. The airfoil models the aerodynamic tip section of a high pressure turbine blade with inlet Mach number of 0.21, exit Mach number of 0.74, pressure ratio of 1.41, Reynolds number of 2.8•106, and total turning of about 100 degrees. The cascade inlet turbulence intensity level is 9%. Tip surface heat transfer coefficient distributions are first shown for a flat, square-edge tip with a clearance gap of 2.03 mm. Heat transfer distributions are then shown for full-perimeter squealer tip cavities having the same clearance gap above the squealer rim, and clearance-to-cavity depth ratios from 0.67 to 2. Regionally averaged heat transfer coefficients are analyzed to discern a relationship between tip heat transfer and cavity depth. Further tests demonstrate the effect of partial squealer rim oxidation, or material loss, on the surface heat transfer distributions.

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