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Cooling/Heat transfer (Volume II)

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A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 20242

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Prof. Dr. Qiang Zhang

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Guest Editor

1.University of Michigan—Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
2. School of Mathematics, Computer Science and Engineering, University of London, London EC1V 0HB, UK
Interests: gas turbine heat transfer and cooling; aerodynamics; conjugate heat transfer; experimental techniques; CFD simulation and validation

Prof. Dr. Shaopeng Lu

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Guest Editor

School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai, China
Interests: gas turbine heat transfer and cooling technology; aerodynamic and heat transfer of turbine blades; mechanism and application of unsteady heat transfer

Special Issue Information

Dear Colleagues,

Our understanding of cooling and heat transfer technology has been continuously improved over the course of several decades. With the development of advanced measurement techniques, experimental research is facing new opportunities and challenges in improving accuracy and resolution, enhancing accessibility, boundary condition control, proper lab scaling methods, etc. With increasing computing power, CFD research now is dealing with new challenges in developing more efficient methods, resolving multiscale problems, unsteady phenomena, and fluid–solid conjugation issues. Meanwhile, further improvements and new thermal management technologies may become more feasible with the recent developments in materials, manufacturing technology, systems integration and controls. It is a great pleasure to collect and share our understandings on the rich physics behind heat transfer mechanisms, as well as new methods and ideas to embrace these opportunities and challenges.

The Special Issue welcomes papers on:

Update of fundamental heat transfer theory;
New internal and external cooling design concepts;
Experimental methods and uncertainty improvement;
High fidelity CFD in cooling/heat transfer;
Conjugate heat transfer experiments and CFD validation.

Prof. Dr. Qiang Zhang
Prof. Dr. Shaopeng Lu
Guest Editors

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Published Papers (7 papers)

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Research

15 pages, 6867 KiB

Open AccessArticle

Development of a Large-Scale High-Speed Linear Cascade Rig for Turbine Blade Tip Heat Transfer Study

by Hongmei Jiang, Xu Peng, Wenbo Xie, Shaopeng Lu and Yongmin Gu

Aerospace 2022, 9(11), 695; https://doi.org/10.3390/aerospace9110695 - 7 Nov 2022

Cited by 5 | Viewed by 1946

Abstract

The high-speed Over-Tip-Leakage (OTL) flow has a significant impact on the aerodynamic performance of the High-Pressure Turbine (HPT) passage and generates high thermal load for the blade tip. Different tip sealing and cooling design strategies are applied to reduce the OTL loss and help turbine survive in a high temperature environment. High-speed linear cascade experimental rigs play an important role in understanding the flow physics and evaluating their performance. Multiple blades and passages are often required to maintain a reasonable flow periodicity. To match the engine representative Reynolds number and Mach number, a high-speed multi-passage cascade design inevitably demands more compressed air supply. A very large amount of heating power is also required if the engine condition wall-to-gas temperature ratio needs to be matched. In this study, a simplified 2-Passage linear cascade rig for high-speed tip heat transfer research was developed. Both the design method and the rig performance are presented. Different from existing design method to match two-dimensional blade loading, this study shows there are other design flexibilities, such as assist blade tip gap, tailboard adjustment, and profiling adjustment, to match the periodic three-dimensional OTL flow structures. The design method was validated by experimental effort. High resolution tip heat transfer coefficient distribution at stationary and rotating conditions (Rotating Mach number = 0.35) are reported. The enlarged test model can offer much more improved resolution of optical measurement near the tip region. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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12 pages, 4819 KiB

Open AccessArticle

Influence of Gas-to-Wall Temperature Ratio on the Leakage Flow and Cooling Performance of a Turbine Squealer Tip

by Dongjie Yan, Hongmei Jiang, Jieling Li, Wenbo Xie, Zhaoguang Wang, Shaopeng Lu and Qiang Zhang

Aerospace 2022, 9(10), 627; https://doi.org/10.3390/aerospace9100627 - 20 Oct 2022

Cited by 4 | Viewed by 1687

Abstract

In high-pressure turbines, there is a large difference in temperature between the mainstream and the turbine blade surface. Most of the turbine blade tip heat transfer studies were conducted under the assumption that the Over-Tip-Leakage (OTL) flow field is independent of the wall thermal condition. Recent numerical and experimental studies have revealed that the two-way coupling effect between aerodynamics and heat transfer should not be neglected. The heat transfer coefficient obtained by the conventional method is not able to match the realistic engine condition accurately. This study investigates the impact of the wall thermal boundary condition on the tip cooling performance of squealer turbine blades. The RANS CFD result was validated against experimental tip heat transfer data obtained from a high-speed test rig with the effect of high-speed relative casing motion. The aerothermal performance for both uncooled and cooled squealer tips was studied at two different gas-to-wall temperature ratios, 1.7 and 1.1; the reference temperature is 204 K. It was found that the location and strength of cavity vortices varied with different wall thermal boundary conditions, leading to different signatures in tip heat transfer and cooling performance. It is recommended that the experimental heat transfer data and film cooling effectiveness obtained at the near-adiabatic wall boundary condition should be corrected before their application to the tip cooling design process. It would be more reliable to match the wall-to-gas temperature ratio during the tip experimental study. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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24 pages, 13516 KiB

Open AccessArticle

Numerical Investigation on Cooling Performance of Rectangular Channels Filled with X-Shaped Truss Array Structures

by Lei Xi, Jianmin Gao, Liang Xu, Zhen Zhao, Zhengheng Yang and Yunlong Li

Aerospace 2022, 9(8), 405; https://doi.org/10.3390/aerospace9080405 - 27 Jul 2022

Cited by 3 | Viewed by 1983

Abstract

In this study, different layout schemes for an X-shaped truss array channel are designed to explore the application of an X-shaped truss array structure in the mid-chord region of turbine blades. The flow and heat transfer performance of X-shaped truss array channels for three layout schemes are numerically investigated. The influence laws of the subchannel height ratio (h/H, 0.2 to 0.4) regarding the cooling performance of the channel with three subchannels are also analyzed. Then, the corresponding heat transfer and friction correlations are obtained. The results show that the layout scheme has significant effects on the flow performance, heat transfer performance and comprehensive thermal performance of X-shaped truss array channels. Among the three layout schemes of X-shaped truss array channels, the single channel has the best flow performance, while the channel with three subchannels has the best heat transfer performance and a comprehensive thermal performance. At different Reynolds numbers, the average Nusselt numbers and comprehensive thermal coefficients of the X-shaped truss array channel with three subchannels range from 38.94% to 63.49% and 27.74% to 46.49% higher than those of a single channel, respectively, and from 5.68% to 18.65% and 11.61% to 21.96% higher than those of the channel with two subchannels, respectively. For the channel with three subchannels, the subchannel height ratio has a great influence on the flow performance, but has a relatively small influence on the heat transfer performance and comprehensive thermal performance of the channel. With the increase in subchannel height ratio, the friction coefficient and average Nusselt number of the channel with three subchannels both show a trend of first increasing and then decreasing, while the comprehensive thermal coefficient shows a slow decreasing trend at higher Reynolds numbers. As a result of comprehensive consideration, the channel with three subchannels at a subchannel height ratio of 0.25 has a better overall cooling performance and is more suitable for cooling the mid-chord region of gas turbine blades. The results may provide a reference for the application of truss array structures in the internal cooling of advanced high-temperature turbine blades in the future. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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21 pages, 10238 KiB

Open AccessArticle

Numerical Investigation on the Heat Transfer of n-Decane in a Horizontal Channel with Axially Nonuniform Heat Flux under Supercritical Pressure

by Jin Zhang, Qilin Zhou, Xudong Zhao, Yuguang Jiang and Wei Fan

Aerospace 2022, 9(6), 326; https://doi.org/10.3390/aerospace9060326 - 17 Jun 2022

Cited by 1 | Viewed by 2293

Abstract

Regenerative cooling is considered promising in the thermal protection of hypersonic propulsion devices such as SCRamjet. However, the heat transfer deterioration (HTD) of hydrocarbon fuel is a severe threat to the thermal structure safety, especially under axially nonuniform heat flux caused by the thermal load difference in different components. In this work, the heat transfer of trans-critical n-decane in a mini-horizontal channel is numerically investigated. The influences of the axially nonuniform heat flux on the heat transfer is focused on. Two types of HTD are recognized and analyzed. The first type of HTD is induced by the near-wall flow acceleration and the local thickening of the viscous sublayer. The second type of HTD is closely related to the expansion of the low thermal conductivity λ and specific heat c_p region, which is seriously worsened under axially nonuniform heat flux, especially when the heat flux peak locates where T_w ≥ T_pc. The minimum HTC deteriorates by 40.80% and the T_{w_max} increases from 857 K to 1071 K by 27.5%. The maximum fluctuation in pressure drop is 6.8% in the variation in heat flux distribution with Φ = 2. This work is expected to offer a reference to the proper match of fuel temperature distribution and the engine heat flux boundary in SCRamjet cooling system design. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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27 pages, 68406 KiB

Open AccessArticle

Numerical Investigation and Parameter Sensitivity Analysis on Flow and Heat Transfer Performance of Jet Array Impingement Cooling in a Quasi-Leading-Edge Channel

by Lei Xi, Jianmin Gao, Liang Xu, Zhen Zhao, Qicheng Ruan and Yunlong Li

Aerospace 2022, 9(2), 87; https://doi.org/10.3390/aerospace9020087 - 9 Feb 2022

Cited by 8 | Viewed by 2269

Abstract

In this study, numerical simulations were carried out to investigate the flow and heat transfer characteristics of jet array impingement cooling in the quasi-leading-edge channel of gas turbine blades. The influence laws of Reynolds number (Re, 10,000 to 50,000), hole diameter-to-impingement spacing ratio (d/H, 0.5 to 0.9), hole spacing-to-impingement spacing ratio (S/H, 2 to 6), and Prandtl number (Pr, 0.690 to 0.968) on flow performance, heat transfer performance, and comprehensive thermal performance were examined, and the corresponding empirical correlations were fitted. The results show that increasing the d/H and reducing the S/H can effectively reduce the pressure loss coefficient in the quasi-leading-edge channel. Increasing the Re, reducing the d/H, and increasing the S/H can effectively enhance the heat transfer effect of the target wall. When d/H = 0.6 at lower Reynolds numbers and S/H = 5 at higher Reynolds numbers, the comprehensive thermodynamic coefficient reaches its maximum values. The average Nusselt numbers and comprehensive thermal coefficients of the quasi-leading-edge channel for steam cooling are both higher than those for air cooling. The pressure loss coefficient of the quasi-leading-edge channel is most sensitive to the change in d/H but is not sensitive to the change in Re. The average Nusselt number of the quasi-leading-edge channel is most sensitive to the change in Re and is least sensitive to the change in Pr. The comprehensive thermal coefficient of the quasi-leading-edge channel is most sensitive to the change in Re. The findings may provide a reference for the design of a steam-cooling structure in the leading edge channel of high-temperature turbine blades. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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20 pages, 7849 KiB

Open AccessArticle

Jet Impingement Heat Transfer Characteristics with Variable Extended Jet Holes under Strong Crossflow Conditions

by Xing Yang, Hang Wu and Zhenping Feng

Aerospace 2022, 9(1), 44; https://doi.org/10.3390/aerospace9010044 - 15 Jan 2022

Cited by 13 | Viewed by 4424

Abstract

In this paper, detailed flow patterns and heat transfer characteristics of a jet impingement system with extended jet holes are experimentally and numerically studied. The jet holes in the jet plate present an inline array of 16 × 5 rows in the streamwise (i.e., the crossflow direction) and spanwise directions, where the streamwise and spanwise distances between adjacent holes, which are normalized by the jet hole diameter (x_n/d and y_n/d), are 8 and 5, respectively. The jets impinge onto a smooth target plate with a normalized distance (z_n/d) of 3.5 apart from the jet plate. The jet holes are extended by inserting stainless tubes throughout the jet holes and the extended lengths are varied in a range of 1.0d–2.5d, depending on the jet position in the streamwise direction. The experimental data is obtained by using the transient thermochromic liquid crystal (TLC) technique for wide operating jet Reynolds numbers of (1.0 × 10⁴)–(3.0 × 10⁴). The numerical simulations are well-validated using the experimental data and provide further insight into the flow physics within the jet impingement system. Comparisons with a traditional baseline jet impingement scheme show that the extended jet holes generate much higher local heat transfer levels and provide more uniform heat transfer distributions over the target plate, resulting in the highest improvement of approximately 36% in the Nusselt number. Although the extended jet hole configuration requires a higher pumping power to drive the flow through the impingement system, the gain of heat transfer prevails over the penalty of flow losses. At the same pumping power consumption, the extended jet hole design also has more than 10% higher heat transfer than the baseline scheme. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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24 pages, 9174 KiB

Open AccessArticle

Cooling Characteristic of a Wall Jet for Suppressing Crossflow Effect under Conjugate Heat Transfer Condition

by Qinghua Deng, Huihui Wang, Wei He and Zhenping Feng

Aerospace 2022, 9(1), 29; https://doi.org/10.3390/aerospace9010029 - 6 Jan 2022

Cited by 12 | Viewed by 3090

Abstract

The leading edge is the critical portion for a gas turbine blade and is often insufficiently cooled due to the adverse effect of Crossflow in the cooling chamber. A novel internal cooling structure, wall jet cooling, can suppress Crossflow effect by changing the coolant flow direction. In this paper, the conjugate heat transfer and aerodynamic characteristics of blades with three different internal cooling structures, including impingement with a single row of jets, swirl cooling, and wall jet cooling, are investigated through RANS simulations. The results show that wall jet cooling combines the advantages of impingement cooling and swirl cooling, and has a 19–54% higher laterally-averaged overall cooling effectiveness than the conventional methods at different positions on the suction side. In the blade with wall jet cooling, the spent coolant at the leading edge is extracted away through the downstream channels so that the jet could accurately impinge the target surface without unnecessary mixing, and the high turbulence generated by the separation vortex enhances the heat transfer intensity. The Coriolis force induces the coolant air to adhere to the pressure side’s inner wall surface, preventing the jet from leaving the target surface. The parallel cooling channels eliminate the common Crossflow effect and make the flow distribution of the orifices more uniform. The trailing edge outlet reduces the entire cooling structure’s pressure to a low level, which means less penalty on power output and engine efficiency. Full article

(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))

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