摘要 :
The endwall heat transfer characteristics of forced flow past bluff bodies have been investigated using liquid crystal thermography (LCT). The bluff body is placed in a rectangular channel with both its ends attached to the endwal...
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The endwall heat transfer characteristics of forced flow past bluff bodies have been investigated using liquid crystal thermography (LCT). The bluff body is placed in a rectangular channel with both its ends attached to the endwalls. The Reynolds number varies from 50,000 to 100,000. In this study, a single bluff body and two bluff bodies arranged in tandem are considered. Due to the formation of horseshoe vortices, the heat transfer is enhanced appreciably for both cases. However, for the case of two bluff bodies in tandem, it is found that the presence of the second bluff body decreases the heat transfer as compared to the case of a single bluff body. In addition, the results show that the heat transfer exhibits Reynolds number similarity. For a single bluff body, the Nusselt number profiles collapse well when the data are scaled by Re~(0.55); for two bluff bodies arranged in tandem, the heat transfer scaling is changed to Re~(0.51), indicating that the power index of Reynolds number is flow dependent.
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Effect of the slashface leakage on the gas turbine blade endwall film cooling and heat transfer performance under three endwall misalignment modes (aligned, cascade and dam) is numerically investigated using the method of solving ...
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Effect of the slashface leakage on the gas turbine blade endwall film cooling and heat transfer performance under three endwall misalignment modes (aligned, cascade and dam) is numerically investigated using the method of solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with the SST k - omega turbulence model. The numerical calculations are conducted with four coolant momentum flux ratios (I) of 0.48, 0.96, 1.42 and 1.87 under three different endwall misalignment modes. The computational results indicate that for the aligned mode, the fore part endwall (z/C-ax < 0.4) cooling effectiveness reaches the maximum when I = 0.96 and the coolant coverage on the back part endwall moves upstream with the increasing coolant momentum. The main high Nu regions concentrate at the back part endwall and the small high heat transfer region at z/C-ax = 0.2 increases the endwall heat transfer coefficient by 8% and 3% for I = 1.42 and 1.87, respectively. As for the cascade misalignment mode, the cooling effectiveness of the fore part endwall decreases sharply with the increasing I. There are mainly two high Nu regions at the fore and middle (0.4 < z/C-ax < 0.7) part endwall caused by misalignment induced vortex. There is also a low Nu region near z/C-ax = 0.9 caused by horseshoe vortex separation, and it can decrease the endwall heat transfer coefficient by 10%. For the dam misalignment mode, the cooling effectiveness is lower but distributes more evenly obstructed by the dam. The horseshoe vortex reattaches on the back part endwall (z/C-ax > 0.7) and causes a high Nu region near z/C-ax = 0.9 that increases the heat transfer coefficient by 20%, which also leads to a cooling protection failure region. Another severe high Nu region at the middle part of the endwall is brought by the separation vortex reattachment. (C) 2018 Elsevier Ltd. All rights reserved.
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In a turbine passage, the wake, which affects the heat transfer of a turbine blade, occurs periodically due to rotation of the blade. We analyzed the effect of wake on the endwall of the turbine blade according to the relative pos...
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In a turbine passage, the wake, which affects the heat transfer of a turbine blade, occurs periodically due to rotation of the blade. We analyzed the effect of wake on the endwall of the turbine blade according to the relative position of the turbine blade and the vane in a stationary condition. The naphthalene sublimation method was used to measure the heat transfer and detached eddy simulation (DES) was used to analyze flow characteristics. The wake from the vane was simulated by using a cylindrical rod upstream of the blade. The cylindrical rod was placed in four which positions that were aligned leading edge-to‑leading edge. The pressure and Q criterion distributions varied according to the position of the upstream wake. As the position of the upstream wake changed, the point at which the passage vortex and wake met varied. Wake and passage vortex met atx/Cx = 0.2 in position 1 and atx/Cx = 0.55 in position 2. After the wake and passage vortex had met, the secondary flow scattered. Therefore, the local and averaged heat transfer varied due to flow characteristics. Thus designers of film cooling holes on endwalls should consider these effects to ensure appropriate cooling performance.
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摘要 :
Modern gas turbines demand effective cooling methods to manage hightemperature
inlet gases (up to 2000ºK) and protect turbine components. One
crucial cooling technique involves casting ribs on the pressure and suction
sides of...
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Modern gas turbines demand effective cooling methods to manage hightemperature
inlet gases (up to 2000ºK) and protect turbine components. One
crucial cooling technique involves casting ribs on the pressure and suction
sides of cooling serpentine passages. These ribs generate vortices that
enhance heat transfer via turbulence promotion. Typically, cooling cascades
feature two types of ribs: straight ribs, which offer a more uniform flow but
lower heat transfer, and inclined ribs, known for higher turbulence and
superior heat transfer capabilities. In the context of turbine blades, inclined
ribs introduce a unique characteristic: secondary flow, which substantially
contributes to heat transfer through turbulence promotion. This study
explores three geometries of recessed endwalls for these ribs using Reynoldsaveraged-
Navier-Stokes (RANS) equations coupled with a k-ω turbulence
model to assess heat transfer characteristics. These endwalls variations aim
to preserve and amplify the secondary flow between the casted ribs. The
results at Re = 19683 demonstrate increased heat transfer in channels with
these new designs. Specifically, the growth of 9.3%, 12.1%, and 14.4% in the
Nusselt number is discovered for the reference triangular, curved, and
trapezoidal endwall designs, respectively. This augmentation in secondary
flow is accompanied by an increase in pressure loss. Consequently, the Heat
Transfer Efficiency Index (HTEI) of the channels increases by 5.2%, 7.0%,
and 8.3% with the new designs compared to the flat endwall at Re = 19683.
Furthermore, when varying the height of the recessions, it becomes evident
that the secondary flow intensifies with increased height. However, the
expansion of friction factors somewhat offsets the substantial Nusselt number
increase. This leads to a 27.0%, 32.7%, and 31.4% HTEI increase at Re =
6844 for the triangular, curved, and trapezoidal endwall designs, respectively.
At Re = 19683, these figures are 13.5%, 18.7%, and 18.1%. These findings
underscore the potential for significant enhancements in heat transfer by
optimizing endwall designs, which can alter the vortex systems within the
channel.
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Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W=76.2 mm, E = 25.4 mm) simulat...
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Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W=76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4E, three different pin-fin height-to-diameter ratios, HID = 4,3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin tip and one of the endwalls, i.e., CID = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs 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. Experimental results reveal that the presence of a detached space between the pin tip and the endwall has a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D, leads to lower heat transfer enhancement and pressure drop. However, C/D = 1, i.e., H/D = 3, of a staggered array configuration exhibits the highest heat transfer enhancement, followed by the cases of C/D = 0 and C/D = 2, i.e., H/D = 4 or 2, respectively.
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The present study aimed to investigate the effect of an unsteady wake on the heat transfer for the endwall surface of a linear of cascade turbine blade. A naphthalene sublimation method was implemented to obtain the detailed heat/...
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The present study aimed to investigate the effect of an unsteady wake on the heat transfer for the endwall surface of a linear of cascade turbine blade. A naphthalene sublimation method was implemented to obtain the detailed heat/mass transfer distributions on the endwall surface. Tests were conducted on a five-passage linear cascade in a low-speed wind tunnel. The effects of unsteady wakes were simulated in the facility by a wake generator consisting of circular rods that were traversed across the inlet flow. The test conditions were fixed at a Reynolds number of 70,000 based on the inlet velocity and chord length. The flow coefficients were varied from 1.3 to 4.2 and the range of Strouhal number was 0.1-0.3. The results showed that the heat transfer distributions differed between steady and unsteady cases. The overall heat transfer for the unsteady cases was higher, and the heat transfer was enhanced with increasing the Strouhal number due to the resulting thin boundary layer and high turbulence intensity. Therefore, a cooling system for the endwall of a rotor should focus on reducing the high temperatures on the endwall surface induced by the unsteady wakes.
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摘要 :Highlights?Heat transfer/film cooling on endwall with different hole-arrangements is studied.?Effect of blowing ratio on heat transfer/film-cooling on endwall is investigated.?Aerodynamic performance in cascade with different film...
展开Highlights?Heat transfer/film cooling on endwall with different hole-arrangements is studied.?Effect of blowing ratio on heat transfer/film-cooling on endwall is investigated.?Aerodynamic performance in cascade with different film cooling is also analyzed.?Predicted Stanton number on endwall compares favorably with the experimental data.?Thermal load at three high heat transfer areas are reduced by the hole-arrangements.AbstractThe RANS (Reynolds Averaged Navier-Stokes) equations were numerically solved to investigate the heat transfer and film cooling effect on the first stage rotor blade endwall in NASA transonic gas turbine. To reduce the thermal load on the upstream of leading edge, shoulder area and corner area of endwall, different film cooling strategies were presented to evaluate the Stanton number, film cooling effectiveness on endwall and also the aerodynamic performance in cascade at three blowing ratios. Through the film cooling upstream leading edge, the area-averagedSton blade endwall is reduced by 1.4% compared with no film cooling case. Through the shoulder area film cooling, the area-averagedStnumber on endwall is reduced by 1%, and the area-averaged film cooling effectiveness is increased by 44.4% atM?=?0.5. With double hole-arrays at the corner area, the area-averagedStnumber on the endwall can be reduced by 1–2%, and the area-averaged film cooling effectiveness can be improved by 10.2–13.6%. The energy loss coefficient in the cascade is almost not affected by the blowing ratio for the leading edge and shoulder area film cooling configurations, while it is sensitive to the blowing ratio for the corner area film cooling.]]>
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摘要 :
The assembly step between the vane and blade in a gas turbine exists because of the rotating blade and expansion of the external flow passage. The assembly step has a great impact on the heat transfer distribution on the endwall. ...
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The assembly step between the vane and blade in a gas turbine exists because of the rotating blade and expansion of the external flow passage. The assembly step has a great impact on the heat transfer distribution on the endwall. In this study, a rod was installed in front of the blade to generate non-uniform inlet flow and to observe the heat transfer characteristics on the endwall. The mass transfer coefficients on the endwall were measured using the naphthalene sublimation method. The results revealed that, as the diameter of the rod increased, a turbulent boundary layer developed.
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A wake is induced in turbine passages due to the interaction of turbine stators and rotors. Each stage of the turbine blade has different geometric parameters, namely, the turning angle, leading edge radius, and solidity, which al...
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A wake is induced in turbine passages due to the interaction of turbine stators and rotors. Each stage of the turbine blade has different geometric parameters, namely, the turning angle, leading edge radius, and solidity, which all vary. Comparison of flow and thermal characteristics between the first and second stage blades was carried out. The flow and thermal characteristics of the first-stage blade endwall were investigated for various Strouhal numbers to determine the wake effect. Numerical simulations and experiments were performed to compare the flow and thermal characteristics of the different stage blades. Experiments were performed using a five-bladed linear cascade with moving cylindrical rods simulating the wake effect. The effective area and strength of secondary vortices differed in each stage of blade, which resulted in different local heat transfer distributions. In addition, the local heat transfer characteristics changed depending on the Strouhal number. The 'without wake' case (St = 0) showed non-uniform heat transfer distributiorpon the endwall with the occurrence of horseshoe, passage and corner vortices. The 'with wake' effect cases (St not equal 0) showed a more uniform heat transfer distribution on the endwall. The wake effect disturbs the occurrence of secondary vortices. With an increase in the Strouhal number, the endwall is exposed to higher thermal load. (C) 2017 Published by Elsevier Inc.
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摘要 :
Detailed heat transfer measurements are necessary to protect the blades under harsh and complex flow conditions. Therefore, this study investigated the heat transfer characteristics on the blade endwall under flow conditions that ...
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Detailed heat transfer measurements are necessary to protect the blades under harsh and complex flow conditions. Therefore, this study investigated the heat transfer characteristics on the blade endwall under flow conditions that simulate high turbulence intensity of the main flow and the generation of wakes by the trailing edge of the vane. The endwall heat transfer was measured using the naphthalene sublimation method. A turbulence generating grid was installed in a linear cascade to simulate the main flow with high turbulence intensity and a wake generator with a rod bundle was used to simulate the wakes generated by the trailing edge of the vane. In the case of high turbulence intensity without wakes, the main flow with high turbulence intensity (turbulence intensity, T.I= 7.5%) had little impact on the effect of the horseshoe vortex and passage vortex on the heat transfer characteristics. However, increasing turbulence caused the endwall heat transfer to decrease near the pressure side of the blade and increase near the suction side of the blade. On the other hand, the wakes resulted in heat transfer characteristics similar to high turbulence intensity but decreased heat transfer by horseshoe vortex and passage vortex. The endwall heat transfer distributions were similar regardless of the turbulence intensity (T.l= 1.2% and 7.5%) in the cases with wakes (rod passing Strouhal number, S = 0.3). The flow condition of S = 0.3 has a more significant influence on the endwall heat transfer than that of T.I = 7.5%.
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