Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

2019 ◽  
Author(s):  
Kai-Chieh Chia ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Three Dimensional Flow ◽  
Smooth Channel ◽  
Blade Tip ◽  
The Impact

Abstract The current study experimentally studied heat transfer characteristics of the blade tip wall in a rotating internal cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180° turn, complex three dimensional flow significantly affected heat transfer on the internal tip surface. The liquid crystal method is used to capture the heat transfer contour on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45° angled ribs. The Reynolds number inside the pressurize two-pass cooling channel ranged from 10,000 to 30,000 at both stationary and rotating conditions. Furthermore, two channel orientations (90° and 135°) were tested. The effect of Coriolis force on heat transfer is studied with the rotation number up to 0.53. The tip heat transfer from the smooth channel wall was more sensitive to rotation and the largest heat transfer enhancement as a result of rotation was 68%.

Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Kai-Chieh Chia ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Cooling Channel ◽  
Rotation Direction ◽  
Smooth Channel ◽  
Blade Tip ◽  
The Impact ◽  
Turn Region

Abstract The tip turn region within the gas turbine blade experienced severe thermal issues related to temperature variations and temperature gradients. The current study experimentally measured the heat transfer distribution of the internal blade tip wall in a rotating cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180 deg turn, complex three-dimensional flow significantly affected the heat transfer on the internal tip surface. The steady-state liquid crystal method was used to obtain a detailed distribution of heat transfer on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45 deg angled ribs. The Reynolds number inside the pressurized cooling channel ranged from 10,000 to 30,000, and the rotation number was up to 0.53. Furthermore, two-channel orientations (90 deg and 135 deg) with respect to the rotation direction were tested. The tip heat transfer from the smooth channel wall was more sensitive to rotation, and the largest heat transfer enhancement caused by rotation was 68%. Channel orientation of 90 deg produced higher heat transfer compared to the orientation of 135 deg.

Numerical Investigation of Rotation Effects on the Flow and Heat Transfer on the Turbine Blade Tip Underside With Bleed Hole at Different Locations

2019 ◽  
Author(s):  
Zhiqi Zhao ◽  
Lei Luo ◽  
Xiaoxu Kan ◽  
Dandan Qiu ◽  
Xun Zhou
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Structural Damage ◽  
Three Dimensional ◽  
Side Wall ◽  
Internal Cooling ◽  
Heat Transfer Augmentation ◽  
Smooth Channel ◽  
Blade Tip ◽  
Cooling Passage

Abstract High thermal load on the turbine blade tip surface leads to high temperature corrosion and severe structural damage. One common way is to deliver a part of coolant through bleed holes onto the tip portion for cooling purpose. In this study, numerical simulations are performed to investigate the effects of rotation on the internal tip heat transfer in a simplified rotating two-pass channel with a bleed hole, which is applicable to the internal cooling passage of typical gas turbine blade. The bleed hole is placed on the tip wall of a two-pass channel at different locations, i.e. the ratio of distance from the outlet-side wall to width of the tip wall is 0.07, 0.21, 0.5, 0.78, 0.93, respectively. A smooth channel without bleed hole is used as Baseline. The Reynolds number is fixed at 10,000. The Ro numbers are varied from 0 to 0.4. Results show that a three-dimensional vortex, which is induced by the Coriolis force, is found at the bend region. It transports the fluid from the trailing side to leading side, which is beneficial to enhance tip heat transfer. The middle-mounted hole shows a better heat transfer augmentation compared to other hole arrangement. The rotation have a notable effect on the heat transfer and flow structures. Compared to the smooth channel, the heat transfer augmentation is about 34%.

Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part II: Experimental Validation

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Filippo Coletti ◽  
Tom Verstraete ◽  
Jérémy Bulle ◽  
Timothée Van der Wielen ◽  
Nicolas Van den Berge ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Internal Cooling ◽  
Transfer Performance ◽  
Cooling Channel ◽  
Piv Measurements ◽  
Cooling Channels ◽  
Numerical Predictions ◽  
The Impact

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper, the design methodology of the cooling channel was presented. In this second part, the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and particle image velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. To assess the impact of the aerodynamic optimization on the heat transfer performance, detailed heat transfer measurements are carried out by means of liquid crystals thermography. The optimized geometry presents overall Nusselt number levels only 6% lower with respect to the standard U-bend. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier–Stokes solver, and a metamodel of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels without leading to a substantial loss in heat transfer performance.

Heat Transfer and Turbulent Flow Characteristics of Isolated Three-Dimensional Protrusions in Channels

1991 ◽  
Vol 113 (3) ◽  
pp. 597-603 ◽  
Author(s):  
P. T. Roeller ◽  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Channel Wall ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Average Heat ◽  
Flow Acceleration ◽  
Dimensional Flow ◽  
Wall Spacing

The flow structure and average heat transfer characteristics of single, isolated three-dimensional protrusions in a flow channel have been investigated experimentally. This configuration has relevance in the electronics industry. The study was designed to identify the influence of the three-dimensional flow around a heated protrusion on its average heat transfer. Heated protrusions varying in width between 0.12 and 1.0 channel widths for a fixed protrusion height and streamwise length were studied in the channel Reynolds number range 500≤Re≤10,000. The channel wall spacing was also varied parametrically between 1.25 and 2.5 streamwise protrusion lengths. The study included both average heat transfer measurements, and detailed local velocity and turbulent flow structure measurements made using laser-Doppler velocimetry. The experimental results show that the Nusselt number increases with both decreasing channel wall spacing and decreasing protrusion width. The increase in heat transfer with decreasing wall spacing is explained by the accelerated flow due to the protrusion-obstructed channel. Increasing Nusselt number with decreasing protrusion width is a result of increased three-dimensional flow and associated turbulent mixing. Both of these flow-related phenomena are illustrated with local mean velocity and turbulence intensity measurements. The presence of recirculation zones both upstream and downstream of the module is revealed. The flow acceleration around the heated protrusions, and three dimensionality of the flow and heat transfer are competing mechanisms; the higher heat transfer due to flow acceleration around the protrusions for larger protrusions goes counter to the trend for higher heat transfer due to increased three-dimensional flow and transport for smaller protrusions. A Nusselt number correlation is developed as a function of channel Reynolds number and protrusion and channel geometric parameters, which describes the tradeoffs discussed.

Rib Spacing Effect on Heat Transfer and Pressure Loss in a Rotating Two-Pass Rectangular Channel (AR=1:2) With 45-Degree Angled Ribs

2006 ◽  
Author(s):  
Yao-Hsien Liu ◽  
Lesley M. Wright ◽  
Wen-Lung Fu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Spacing Effect ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Smooth Channel

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and non-rotating rectangular, cooling channels. In the 1:2 rectangular channels, 45° angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross-section are used for all spacings, so the height-to-hydraulic diameter (e/Dh) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3, has the best thermal performance in both rotating and non-rotating channels. This close spacing yields the greatest heat transfer enhancement, while the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.

Performance Evaluation of a Modified Cross Section Grooved Channel as Turbulence Promoter in Internal Cooling Channel of a Gas Turbine Blade

2015 ◽  
Author(s):  
Krishnendu Saha ◽  
Deoras Prabhudharwadkar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Cross Section ◽  
Channel Wall ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Ribbed Channel ◽  
Baseline Case ◽  
Mainstream Flow

Internal cooling channel in gas turbine blades use ribs as turbulence promoter to increase local turbulence and improve heat transfer from hot wall to coolant air flowing through the internal cooling channels. The ribs protrude into the flow and result in a significant pressure drop of the coolant air. Indentations like grooves in the cooling channel wall can also be used as turbulence promoters to enhance local heat transfer and as they do not protrude into the mainstream flow, the pressure drop penalty could be much lesser than a conventional ribbed channel. A numerical study is conducted under stationary condition on a square cross section channel representing an internal cooling channel of a turbine airfoil. Some standard and modified cross sections of grooved channel are used as turbulence promoters with a goal to enhance heat transfer from the internal cooling channel wall with minimal pressure drop. The steady state solution is based on using the Reynolds Averaged Navier-Stokes (RANS) equation and k-omega-SST turbulence model. Numerical calculations are done at four Reynolds numbers (Re=15000, 30000, 68000 and 88000) based on fluid properties at the inlet of the internal cooling channel. The grooves are placed on two opposite sides of the square cross section channel and other two walls are smooth walls without any turbulence promoters. A hemispherical cross section continuous groove which is placed perpendicular to the mainstream flow direction is taken as baseline case and a teardrop shaped groove is used to compare the performance difference between the two groove cross section. A broken shaped angled groove configuration with the teardrop cross section groove is also investigated to find the relative performance improvement with the baseline case. Performance comparison with standard 90° rib geometry is done to understand the overall effectiveness of the grooved geometries with respect to common standard in gas turbine blade internal cooling. The straight teardrop cross section groove improves the heat transfer values compared to the hemispherical cross section groove by 8–12% and the broken angled teardrop groove case improves heat transfer by 11–14% compared to the hemispherical cross section groove case. The pressure drop produced by all the groove geometries is about the same. It is seen that the broken angled groove can produce the same heat transfer enhancement compared to a 90° ribbed channel but the pressure drop is more than 3 times lesser compared to the ribbed case. Considering the heat transfer and pressure drop, an increase in thermal performance factor of 37–41% is seen for the angled grooved case compared to the 90° ribbed geometry.

Effect of Coriolis and Centrifugal Forces on Turbulence and Heat Transfer at High Rotation and Buoyancy Numbers in a Rib-Roughened Internal Cooling Channel

2004 ◽  
Author(s):  
A. K. Sleiti ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Centrifugal Forces ◽  
Reynolds Stresses ◽  
Rsm Model ◽  
Density Ratios ◽  
Rib Roughened

Prediction of three-dimensional flow field and heat transfer in a two pass rib-roughened square internal cooling channel of turbine blades with rounded staggered ribs rotating at high rotation and density ratios is the main focus of this study. Rotation, buoyancy, ribs, and geometry affect the flow within these channels. The full two-pass channel with bend and with rounded staggered ribs with fillets (e/Dh = 0.1 and P/e = 10) as tested by Wagner et. al [1992] is investigated. RSM is used in this study and enhanced wall treatment approach to resolve the near wall viscosity-affected region. RSM model was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotational numbers (0.24, 0.475, 0.74 and 1) and high-density ratios (0.13, 0.23, and 0.3). Particular attention is given to how secondary flow, Reynolds stresses, turbulence intensity, and heat transfer are affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and density ratios. A linear correlation for 4-side-average Nusselt number as a function of rotation number is derived.

Heat Transfer and Pressure Loss Characteristics of a Narrow Internal Cooling Passage at Low Reynolds Number

2014 ◽  
Author(s):  
Sin Chien Siw ◽  
Nicholas Miller ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Internal Cooling ◽  
Hybrid Technique ◽  
Pin Fin ◽  
Smooth Channel ◽  
Cooling Passage ◽  
Pin Fin Array

This paper describes a detailed experimental investigation of a narrow rectangular channel based on the double-wall cooling concept that can be applicable to a gas turbine airfoil. The channel has dimensions of 63.5 mm by 12.7 mm, corresponding to an aspect ratio of 5:1. A single pin-fin element, arranged in 9 rows is fitted into the channel. The pin diameter, D, is 12.7 mm, and the ratio of pin-height-to-diameter, H/D is 1. The pins are arranged based on the typical inter-pin spacing of 2.5D in both spanwise and streamwise directions. The Reynolds number, based on the hydraulic diameter of the pin fin and the mean bulk velocity, ranges from 6,000 to 15,000. The experiments employ a hybrid technique based on transient liquid crystal imaging to obtain the distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Commercially available CFD software, ANSYS CFX, is used to qualitatively correlate the experimental results and to provide detailed insights of the flow field created by the array.The heat transfer on both the endwall and pin-fin surfaces revealed similar pattern compared to the typical circular pin-fin array, which were conducted at higher Reynolds number. The total heat transfer enhancement of current pin-fin array is approximately five times higher than that of fully developed smooth channel with low pressure loss, which resulted in much higher thermal performance compared to other pin-fin array as reported in the literature.

Flow and Heat Transfer of Air and Steam in Internal Cooling Passages of Turbine Blade

2010 ◽  
Author(s):  
Xinjun Wang ◽  
Wei Wang ◽  
Luke Chou ◽  
Yumeng Han ◽  
Liang Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Grid Generation ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Heat Transfer Efficiency ◽  
Flow And Heat Transfer ◽  
Key Factor ◽  
The Impact

Numerical prediction of three-dimensional flow and heat transfer of air and steam are presented for serpentine cooling channels by using the commercial software CFX. The results show that SSG model is the best turbulence model for the ribbed channels. A study of Grid Generation was performed for flow and heat transfer in serpentine cooling channels, with the same turbulence model. And the results show that the space between the first node and the wall surface (Δy) is 0.0001 mm and the grid density is 1.3 or Δy of 0.001 mm and grid density of 1.2 is the appropriate choice for grid generation. Ribbed channels are not sensitive to mesh generation compared with smooth passages. With the same inlet flux, steam heat transfer efficiency is higher than that of air about 15–20%; steam superheat degree is not the key factor for heat transfer, but it had an effect on flow resistance. Compared with smooth channels, ribbed channels reduce the impact of the turn; the best heat transfer regions appear downstream of the turn. V-type ribs have better heat transfer performance than the parallel type ribs; the highest heat transfer occurs in the section between the ribs.

scholarly journals Effects of Gaps Between Side-Walls and60∘Ribs on the Heat Transfer and Rib Induced Secondary Flow Inside a Stationary and Rotating Cooling Channel

2001 ◽  
Vol 7 (6) ◽  
pp. 425-433
Author(s):  
Robert Kiml ◽  
Sadanari Mochizuki ◽  
Akira Murata
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Three Dimensional Flow ◽  
Side Walls ◽  
Visualization Experiments

The present study investigates the effects of gaps between the side-walls and60∘ribs on the local heat transfer distribution between two consecutive ribs. The heat transfer and flow visualization experiments were carried out inside a straight rib-roughened duct with the ribs mounted on two opposite side walls with and without the gaps. The results showed that the existence of the gaps appreciably enhances the Nu in the area between two consecutive ribs. It is caused by (1) the introduction of the fresh air through the gaps into this region, and (2) the improvement of the three-dimensional flow structure in the area between the two ribs.

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