Comparison of Continuous and Truncated Ribs on Internal Blade Tip Cooling

2012 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbine Blades ◽  
Ccd Camera ◽  
Outer Wall ◽  
Transfer Coefficients ◽  
Duct Geometry ◽  
Blade Tip ◽  
Cooling Passage ◽  
Cooling Air

In the present work, an experimental study related to turbulent flow inside the bend part of a U-duct geometry was performed concerning pressure drop and heat transfer. Such duct geometries can be found inside gas turbine blades, where the cooling air extracts heat from hot internal walls while it is flowing inside the cooling passage. Both friction factors and convective heat transfer coefficients were established inside the bend part of the U-duct for two different rib cases, namely continuous and truncated ribs with varying Reynolds number from 8,000 to 20,000. For the continuous rib case, the length of the ribs was equal to the height of the duct while in the truncated rib case two different rib lengths, i.e., 46 mm and 40 mm, respectively, were considered. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratio was 10. The test rig has been built in such a way that various experimental setups can be handled as the outer wall of the bend (turn) part of the U-duct can easily be removed and the ribs can be changed. Both the U-duct and the ribs were made from acrylic material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on the narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The ribs were placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The pressure drop was almost identical for the continuous and truncated rib cases, while the heat transfer coefficient is 10% higher for the continuous rib case at Re = 20000. The uncertainties in the evaluated properties were 3% and 6% for the Nusselt number and friction factor, respectively.

Effects of Ribs on Internal Blade-Tip Cooling

2011 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Turbine Blades ◽  
Ccd Camera ◽  
Transfer Coefficients ◽  
Cooling Flow ◽  
Friction Factors ◽  
Blade Tip

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct with relevance for tip cooling of gas turbine blades. The U-duct models the internal blade cooling flow passages. Both friction factors and convective heat transfer coefficients were measured along the bend (turn) part of the U-duct for three different rib configuration cases, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs with three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratios were 10 and 20. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configurations can be changed. The surface temperature was measured by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. Both the friction factor and heat transfer coefficient were affected by the position and configuration of the ribs along the bend wall. The highest friction factor was found for two ribs placed at the middle and outlet positions of the bend wall, respectively. The highest heat transfer coefficient was found for two ribs placed at the inlet and middle positions of the bend wall, respectively. The uncertainties in the experiments were estimated to be 3% and 6% for the Nusselt number and friction factor, respectively.

Comparison of Pressure Drop and Endwall Heat Transfer Measurements to Flow Visualization Testing of Solid and Porous Pin Fin Arrays

2009 ◽  
Author(s):  
Jared M. Pent ◽  
Jay S. Kapat ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Visualization ◽  
Local Heat Transfer ◽  
Ccd Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Porous Aluminum ◽  
Pin Fins ◽  
A Charge

This paper examines the local and averaged endwall heat transfer effects of a staggered array of porous aluminum pin fins with a channel blockage ratio (blocked channel area divided by open channel area) of 50%. Two sets of pins were used with pore densities of 0 (solid) and 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates using each set of pins. Local heat transfer coefficients on the endwall were measured using Thermochromatic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. The heat transfer and pressure data was then compared to flow visualization tests that were run using a fog generator. Results are presented for the two sets of pins with Reynolds numbers between 25000 and 130000. Local HTC (heat transfer coefficient) profiles as well as spanwise and streamwise averaged HTC plots are displayed for both pin arrays. The thermal performance was calculated for each pin set and Reynolds number. All experiments were carried out in a channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72.

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.

Analysis of Enhanced Heat Transfer on a Turbine Blade Tip-Wall With and Without Guide Ribs

2010 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n ◽  
Weihong Zhang ◽  
Esa Utriainen ◽  
Lieke Wang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Turbulent Heat Transfer ◽  
Channel Height ◽  
Turbulent Heat ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Numerical Predictions ◽  
Blade Tip

Cooling methods are needed for gas turbine blade tips that are exposed to high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. This paper presents numerical predictions of turbulent heat transfer through two-pass channels with and without guide ribs (guide vanes) placed in the turn regions using RANS turbulence modeling. The effects of adding guide ribs on the tip-wall heat transfer enhancement and the channel pressure drop have been analyzed. The inlet Reynolds numbers are ranging from 100,000 to 600,000, and the rib cross-section blockage ratio (rib height to channel height, 2e/H) is 0.182. The detailed fluid flow and heat transfer over the tip-wall are presented. The overall performances of three two-pass channels are evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide ribs are 20%∼50% higher than that of a channel without guide ribs. The presence of guide ribs could lead to an increased (about 15%) or decreased (up to about 12%) pressure drop, depending upon the geometry and placement of guide ribs. It is suggested that the usage of guide ribs is a suitable way to improve the flow structure and augment the blade tip heat transfer, but is not the most effective way to augment tip-wall heat transfer compared to the augmentation by surface modifications imposed on the tip directly.

scholarly journals Experimental Study of the Effects of Bleed Holes on Heat Transfer and Pressure Drop in Trapezoidal Passages With Tapered Turbulators

1993 ◽  
Author(s):  
M. E. Taslim ◽  
T. Li ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Continuous Change ◽  
Trailing Edge ◽  
Aspect Ratios ◽  
Mainstream Flow ◽  
Cooling Passage ◽  
Cooling Air

Trailing edge cooling cavities in modern gas turbine blades often have trapezoidal cross-sectional areas of relatively low aspect ratio. To enhance cooling effectiveness in these passages, they are roughened with tapered turbulators. Furthermore, to provide additional cooling for the trailing edge, the cooling air may be ejected through trailing edge slots as it moves radially along the cooling passage. The tapered turbulators, in conjunction with the presence of these slots along the smaller base of the trapezoidal cavity, create spanwise as well as longitudinal variations in heat transfer coefficient on the turbulated walls. Moreover, the continuous variation of cooling air velocity along these passages causes a continuous change in static pressure which also requires investigation. Liquid crystals are used in this experimental investigation to study the effects of tapered turbulators on heat transfer coefficients in trailing edge passages with and without bleed holes. The tapered turbulators are configured on two opposite walls of the trapezoidal test section in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90°. Nine different test geometries consisting of two passage aspect ratios, AR, were tested over a range of turbulator aspect ratios, ARt, blockage ratios, emax/Dh, pitch-to-height ratios, S/emax, and Reynolds numbers. Channel pressure losses were also measured and both heat transfer and friction factor results for several geometries are compared. It is concluded that a) there exists a large spanwise variation in heat transfer coefficient in test sections with no bleed holes, b) adding bleed holes to the smaller base of the trapezoidal cavity gives a spanwise velocity component to the mainstream flow and reduces this variation, and c) Nusselt numbers measured in the test sections with bleed holes correlate well with local Reynolds number.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Partial Length Pin-Fins

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Slight Reduction ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Partial Length ◽  
Pin Fins ◽  
Cooling Passage

Abstract In the current study, the heat transfer and pressure drop characteristics of a rotating, partial pin-finned, cooling channel that has a trapezoidal cross section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. To model the geometry of an internal trailing edge cooling passage, the channel is oriented with respect to the direction of rotation (β = 120 deg). Isolated copper plates are used to obtain regionally averaged heat transfer coefficients on the leading and trailing surfaces. Pressure drop is measured using pressure taps placed at the inlet and outlet of the channel. Utilizing Dp = 5 mm diameter pins, a staggered array is created. For this array, the streamwise pin-spacing, Sy/Dp = 2.1, was kept constant; however, the spanwise pin-spacing, Sx/Dp, was varied from the hub to tip between 3 and 2.6 due to the channel convergence. Experiments were conducted for two partial pin-fin sets having pin length-to-diameter ratios of Sz/Dp = 0.4 and 0.2. The rotation number was varied from 0 to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300 rpm. A significant decrease in pressure loss and a slight reduction in heat transfer enhancement are observed with the use of partial pin-fins compared with the previously reported full pin-fin converging channel study. This provides better thermal performances of the partial pin-fin arrays compared with the full pin-fin array, in the converging channels.

Experimental Study of the Effects of Bleed Holes on Heat Transfer and Pressure Drop in Trapezoidal Passages With Tapered Turbulators

1995 ◽  
Vol 117 (2) ◽  
pp. 281-289 ◽  
Author(s):  
M. E. Taslim ◽  
T. Li ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Continuous Change ◽  
Trailing Edge ◽  
Aspect Ratios ◽  
Mainstream Flow ◽  
Cooling Passage ◽  
Cooling Air

Trailing edge cooling cavities in modern gas turbine blades often have trapezoidal cross-sectional areas of relatively low aspect ratio. To enhance cooling effectiveness in these passages, they are roughened with tapered turbulators. Furthermore, to provide additional cooling for the trailing edge, the cooling air may be ejected through trailing edge slots as it moves radially along the cooling passage. The tapered turbulators, in conjunction with the presence of these slots along the smaller base of the trapezoidal cavity, create both spanwise and longitudinal variations in heat transfer coefficient on the turbulated walls. Moreover, the continuous variation of cooling air velocity along these passages causes a continuous change in static pressure, which also requires investigation. Liquid crystals are used in this experimental investigation to study the effects of tapered turbulators on heat transfer coefficients in trailing edge passages with and without bleed holes. The tapered turbulators are configured on two opposite walls of the trapezoidal test section in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90 deg. Nine different test geometries consisting of two passage aspect ratios, AR, were tested over a range of turbulator aspect ratios, ARt, blockage ratios, emax/Dh, pitch-to-height ratios, S/emax, and Reynolds numbers. Channel pressure losses were also measured and both heat transfer and friction factor results for several geometries are compared. It is concluded that (a) there exists a large spanwise variation in heat transfer coefficient in test sections with no bleed holes, (b) adding bleed holes to the smaller base of the trapezoidal cavity gives a spanwise velocity component to the mainstream flow and reduces this variation, and (c) Nusselt numbers measured in the test sections with bleed holes correlate well with local Reynolds number.

scholarly journals Heat Transfer in a Rotating Radial Channel With Swirling Internal Flow

1998 ◽  
Author(s):  
B. Glezer ◽  
H. K. Moon ◽  
J. Kerrebrock ◽  
J. Bons ◽  
G. Guenette
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Internal Flow ◽  
Leading Edge ◽  
Negative Influence ◽  
Coolant Temperature ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Channel Diameter ◽  
Cooling Passage

This paper presents experimental results for heat transfer in swirling internal flow, obtained in two ways. A test rig simulated a rotating blade’s leading edge internal passage with heated walls and screw-shaped cooling swirl generated by flow introduced through discrete tangential slots. Spatially resolved variations of the surface heat transfer coefficients were measured in the rotating rig using an IR radiometer. A blade tested in the actual engine environment had similar geometry of the leading edge cooling passage. The blade surface temperatures were mapped in the engine with thermal paints and compared with a traditional convective cooling configuration. The data from the rotating rig and engine measurements are also compared with non-rotating heat transfer results obtained in the hot cascade using a traversing pyrometer at a realistic wall-to-coolant temperature ratio. The results are presented for realistic rotational numbers, ranging from 0 to 0.023, and for representative Reynolds number of 20,000 based on the channel diameter. The effect of Coriolis forces is evident with the change of direction of the rotation. A slight negative influence of the crossflow, which increased toward the outer radius of the channel, was recorded in the rig test results. The results presented will assist in better understanding of the screw-shaped swirl cooling technique, providing the next step toward the application of this highly-effective internal cooling method for the leading edges of turbine blades.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Smooth Walls and Pin-Fins

2020 ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Heat Transfer Coefficients ◽  
Pin Fins ◽  
Cooling Passage

Abstract The heat transfer and pressure drop characteristics of a rotating cooling channel that has an angled trapezoidal cross-section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. The channel is oriented 120° with respect to the direction of rotation to model the geometry of an internal, trailing edge cooling passage. Both the leading and trailing sides of the channel are divided into three and six regions in the spanwise and streamwise directions, respectively. The copper plate method is used to obtain regionally averaged heat transfer coefficients. The pressure drop is measured utilizing pressure taps placed at the inlet and outlet of the channel. Experiments were conducted with the inlet Reynolds number ranging from 10,000 to 40,000. The rotational speed varies from 0 rpm to 300 rpm, resulting in the highest rotation number of 0.21. The effects of full pin-fins on the heat transfer and pressure drop characteristics are obtained and compared to the smooth surface converging channel results. The impact of the convergence, which causes variations of flow and geometric parameters through the passage, such as aspect ratio, Reynolds number, and rotation number, on the heat transfer coefficients and pressure drop are addressed. Results show that due to the 120° channel orientation, rotation has a positive impact on the leading and trailing surface heat transfer. Furthermore, the convergence decreases the aspect ratio while increasing Reynolds number. The convergence significantly enhances heat transfer on both the leading and trailing surfaces along the streamwise and spanwise directions. The convergence also reduces the rotation effect in the streamwise direction for a given mass flow rate.

Numerical Investigation of Convective Heat Transfer and Pressure Drop for Ribbed Surfaces in the Bend Part of a U-Duct

2012 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Gas Turbine Blades ◽  
Cross Section Area ◽  
Duct Geometry ◽  
Energy Equations

This work concerns two-dimensional numerical simulations of the flow and temperature fields inside smooth and ribbed bend (turn) parts of a U-duct with relevance for internal tip cooling of gas turbine blades. The ribs are placed internally on the outermost bend surface. The renormalization group (RNG) k-ε turbulence model was used to solve the momentum and energy equations inside the bend (turn) part as well in the supply and return straight parts of the U-duct. For the ribbed surface three different rib configurations were simulated, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs for three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1, the pitch ratios were 13.5 and 27 and the Reynolds number was 20000. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2, the inside length of the bend part was 240 mm. The results were compared with experimental data obtained at similar conditions. The numerical results were closer to the experimental ones for those cases with the rib at the inlet position than for the cases with the rib at the middle position. The case of two ribs at the inlet and middle gave the highest heat transfer coefficients while the case of a single rib at the middle gave the highest local pressure coefficient of all cases.

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