Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring a Converging Tip Turn With Various 45 deg Rib Coverage Designs

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Copper Plate ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
First Passage ◽  
Pressure Loss Coefficient ◽  
Internal Surfaces ◽  
Turbine Airfoils

Varying aspect ratio (AR) channels are found in modern gas turbine airfoils for internal cooling purposes. Corresponding experimental data are needed in understanding and assisting the design of advanced cooling systems. The present study features a two-pass rectangular channel with an AR = 4:1 in the first pass with the radial outward flow and an AR = 2:1 in the second pass with the radial inward flow after a 180 deg tip turn. Effects of rib coverage near the tip region are investigated using profiled 45 deg ribs (P/e = 10, e/Dh ≈ 0.11, parallel and in-line) with three different configurations: less coverage, medium coverage, and full coverage. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage. The highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Heat transfer coefficients on the internal surfaces were obtained by the regionally averaged copper plate method. The results showed that the rotation effects on both heat transfer and pressure loss coefficient are reduced with an increased rib coverage in the tip turn region. Different rib coverage upstream of the tip turn significantly changes the heat transfer in the turn portion. Heat transfer reduction (up to −27%) on the tip wall was seen at lower Ro. Dependence on the Reynolds number can be seen for this particular design. The combined geometric, rib coverage, and rotation effects should be taken into consideration in the internal cooling design.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (AR=4:1 to 2:1) With Profiled 60 Deg Angled Ribs

2018 ◽  
Author(s):  
Andrew F. Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Cross Section ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Internal Cooling ◽  
First Passage ◽  
Aspect Ratios

The internal cooling channels of an advanced gas turbine blade typically have varying aspect ratios from one pass to another due to the varying thickness of the blade profile. Most of the fundamental internal cooling studies found in the open literature used a fixed aspect ratio for multi-pass channels. Studies on a reduced cross-section and aspect ratio channel are scarce. The current study features a two-pass rectangular channel with an aspect ratio AR = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180 deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross-section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ≈ 0.11, parallel and inline). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all surfaces within the flow passages. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Rotation effects on both heat transfer and pressure loss coefficient for the smooth and rib-roughened cases are presented. The results showed that the turn induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction on the tip wall was seen in both the smooth and ribbed cases under rotating condition. A reduced overall pressure penalty was seen for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

Regional Heat Transfer and Pressure Drop in Two-Pass and Three-Pass Flow Passages With 180-Degree Sharp Turns

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through a two-pass (one-turn) and a three-pass (two-turn) passages with 180-degree sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross-section and length-to-height ratio of 8. The passage surface, including top wall, side walls and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very non-uniform mass transfer coefficients measured around a sharp 180-degree turn exhibit the effects of flow separation, reattachment and impingement, in addition to secondary flows. Results of the three-pass passage indicate that heat transfer characteristics around the second turn is virtually the same as that around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45% to 65% of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15% higher than that of the two-pass one. This 15% increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages varies significantly with the Reynolds number.

scholarly journals Pressure Drop Distribution in a Rotating Rectangular Channel With One Ribbed Surface

1997 ◽  
Author(s):  
S. V. Prabhu ◽  
R. P. Vedula
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Turbine Rotor ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Turbine Rotor Blade ◽  
Blade Thickness

A modified geometry for the internal cooling passages of a gas turbine rotor blade is suggested here. In this modified geometry, the Coriolis force induced enhanced heat transfer coefficients are experienced by both the coolant channel walls adjacent to the blade pressure and blade suction surfaces. This is made possible by permitting the flow to have a radially outward and a radially inward direction at different locations along the blade thickness at a given chordwise location. However, the flow geometry is complex and the corresponding pressure losses are also likely to be larger. The present investigation is a preliminary study of the pressure drop characteristics for the modified channel suggested above and the simplest case of a straight channel with ribs on only one surface is reported here. The pressure drop in a rectangular cross-sectioned duct with an aspect ratio of 2.0 rotating about an axis normal to the free-stream direction in the presence of rib turbulators glued on one of the surfaces of the test section with ribs normal to the flow direction is measured. The study has been conducted for Reynolds number varying from 10000–17000 and the rotation number varying from 0–0.21. Experiments were carried out for various pitch-to-rib height ratios (P/e) of 3, 5, 7.5 & 10 with a constant rib height-to-hydraulic diameter ratio (e/D) of 0.15. A significant increase of the friction factor is observed when the ribbed surface is the coolant channel trailing (pressure) surface in the presence of rotation. The highest friction factor is observed in a channel with a P/e ratio of 5 which would imply that there could be a significant increase in the heat transfer coefficient for this configuration. A pitch-to-height ratio of about 10, which is the most preferred choice for a stationary configuration, no longer appears to be the optimum in the presence of rotation.

Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR = 4) With V-Shaped Ribs by a Reynolds Stress Turbulence Model

2003 ◽  
Author(s):  
Guoguang Su ◽  
Shuye Teng ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Heat Fluxes ◽  
Reynolds Stresses ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Flow And Heat Transfer

Computations were performed to study three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with 45° V-shaped ribs. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio (e/Dh) is 0.078 and the rib-pitch-to-height ratio (P/e) is 10. A total of eight calculations have been performed with various combinations of rotation number, Reynolds number, coolant-to-wall density ratio, and channel orientation. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number varied from 10,000 to 500,000. Three channel orientations (90°, −135°, and 135° from the rotation direction) were also investigated. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, turbulent Reynolds stresses, and heat fluxes and heat transfer coefficients.

Effect of Plenum Length and Diameter on Turbulent Heat Transfer in a Downstream Tube and on Plenum-Related Pressure Losses

1981 ◽  
Vol 103 (3) ◽  
pp. 415-422 ◽  
Author(s):  
S. C. Lau ◽  
E. M. Sparrow ◽  
J. W. Ramsey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient

A systematic experimental study was carried out to determine how the heat transfer characteristics of a turbulent tube flow are affected by the length and diameter of a cylindrical plenum chamber which delivers fluid to the tube. The net pressure loss due to the presence of the plenum was also measured. The experimental arrangement was such that the fluid experiences a consecutive expansion and contraction in the plenum before entering the electrically heated test section. Air was the working fluid, and the Reynolds number was varied over the range from 5,000 to 60,000. It was found that at axial stations in the upstream portion of the tube, there are substantially higher heat transfer coefficients in the presence of longer plenums. Thus, a longer plenum functions as an enhancement device. On the other hand, the plenum diameter appears to have only a minor influence in the range investigated (i.e., plenum diameters equal to three and six times the tube diameter). The fully developed Nusselt numbers are independent of the plenum length and diameter. With longer plenums in place, the thermal entrance length showed increased sensitivity to Reynolds number in the fully turbulent regime. The pressure loss coefficient, which compares the plenum-related pressure loss with the velocity head in the tube, increases more or less linearly with the plenum length. With regard to experimental technique, it was demonstrated that guard heating/cooling of the electrical bus adjacent to the tube inlet is necessary for accurate heat transfer results at low Reynolds numbers but, although desirable, is less necessary at higher Reynolds numbers.

Establishing a Methodology for Resolving Convective Heat Transfer From Complex Geometries

2008 ◽  
Author(s):  
J. Ostanek ◽  
K. Thole ◽  
J. Prausa ◽  
A. Van Suetendael
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Model Approximation ◽  
Lumped Model ◽  
Smooth Channel ◽  
Loop Channel ◽  
Turbine Airfoils

Current turbine airfoils must operate at extreme temperatures, which are continuously driven higher by the demand for high output engines. Internal cooling plays a key role in the longevity of gas turbine airfoils. Ribbed channels are commonly used to increase heat transfer by generating turbulence and to provide a greater convective surface area. Because of the increasing complexity in airfoil design and manufacturing, a methodology is needed to accurately measure the convection coefficient of a rib with a complex shape. Previous studies that have measured the contribution to convective heat transfer from the rib itself have used simple rib geometries. This paper presents a new methodology to measure convective heat transfer coefficients on complex ribbed surfaces. The new method was applied to a relatively simple shape so that comparisons could be made with a commonly accepted method for heat transfer measurements. A numerical analysis was performed to reduce experimental uncertainty and to verify the lumped model approximation used in the new methodology. Experimental measurements were taken in a closed-loop channel using fully rounded, discontinuous, skewed ribs oriented 45° to the flow. The channel aspect ratio was 1.7:1 and the ratio of rib height to hydraulic diameter was 0.075. Heat transfer augmentation levels relative to a smooth channel were measured to be between 4.7 and 3 for Reynolds numbers ranging from 10,000 to 100,000.

scholarly journals Heat Transfer-Friction Characteristic Comparison in Rectangular Channel Arrays of Attached, Detached, and Alternate Attached-Detached Ribs on Two Opposite Walls

1997 ◽  
Author(s):  
Jenn-Jiang Hwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Hydraulic Diameter ◽  
Channel Height ◽  
Moderate Pressure ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Friction Characteristic

Experiments are conducted to study the effect of three types of rib-arrays, namely composite, fully-attached, and fully-detached ribs, on friction factors and center-line heat transfer coefficients in rectangular channels. Two opposite walls are roughened by alternate attached and detached in-line rib-arrays for the composite ribs. The Reynolds number (Re) based on channel hydraulic diameter ranges from 12,000 to 70,000; whereas the rib pitch-to-height ratio varies from 10 to 30. The rib-to-channel height ratio (or rib height-to-channel hydraulic diameter ratio), and the ratio of the rib clearance to height are fixed at h/2B = 0.2 (h/De = 0.125), and c/h = 0.5, respectively, with a channel aspect ratio (W/B) of 4.0. It takes a longer distance from the channel inlet to set the local heat transfer coefficient into a periodic constant-value distribution for the composite-ribbed wall due to the more complex turbulent transportation. In the fully developed flows, the composite rib-roughened wall yields the highest heat transfer augmentation, and gives moderate pressure-drop penalty among the three types of ribbed walls. Performance evaluation under the constant pumping-power constraint reveals that the composite-ribbed channel performs best of the three ribbed arrangements. Semi-empirical correlations for friction and heat transfer in composite-ribbed channels are developed to account for rib spacing and Reynolds number for the design of gas turbine blade cooling passages.

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.

Heat Transfer at High Rotation Numbers in a Two-Pass 4:1 Aspect Ratio Rectangular Channel With 45-Degree Skewed Ribs

2006 ◽  
Author(s):  
Fuguo Zhou ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Published Data ◽  
Channel Measurements ◽  
First Passage ◽  
Square Channel ◽  
Smooth Channel

Heat transfer measurements are reported for a rotating 4:1 aspect ratio (AR) coolant passage with ribs skewed 45 degree to the flow. The study covers Reynolds number (Re) in the range of 10,000–70,000, rotation number (Ro) in the range of 0–0.6, and density ratios (DR) between 0.1–0.2. These measurements are done in a rotating heat transfer rig utilizing segmented copper pieces that are individually heated, and thermocouples with slip rings providing the interface between the stationary and rotating frames. The results are compared with the published data obtained in a square channel with similar dimensionless rib-geometry parameters, and with the results obtained for a 4:1 AR smooth channel. As in a 1:1 AR channel, rotation enhances the heat transfer on the destabilized walls (inlet-trailing wall and outlet-leading wall), and decreases the heat transfer ratio on the stabilized walls (inlet-leading wall and outlet-trailing wall). However, the rotation-induced enhancement/degradation for the 4:1 rectangular channel is much weaker than that in the square ribbed channel, especially in the inlet (the first passage). The results on the inlet-leading wall are in contrast to that in the smooth channel with the same AR, where rotation causes heat transfer to increase along the inlet-leading wall at lower Reynolds number (Re = 10,000 and 20,000). Higher DR is observed to enhance the heat transfer on both ribbed walls in the inlet (the first passage) and the outlet (the second passage), but the DR effects are considerably weaker than those in a ribbed square channel. Measurements have also been parameterized with respect to the buoyancy parameter and results show the same general trends as those with respect to the rotation number. In addition, pressure drop measurements have been made and the thermal performance factor results are presented.

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