| 1. |
- Lei, Luo, et al.
(författare)
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Computational investigation of dimple effects on heat transfer and friction factor in a Lamilloy cooling structure
- 2015
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Ingår i: Journal of Enhanced Heat Transfer. - 1563-5074. ; 22:2, s. 147-175
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Tidskriftsartikel (refereegranskat)abstract
- Good heat transfer performance with a moderate pressure drop penalty contributes to the gas turbine engine lifetime and guaranteeing engine efficiency. In this study, the dimple effects for a Lamilloy (R) (Allison Advanced Development Corporation, Indiana, IN, USA) cooling structure on the heat transfer and friction factor are numerically investigated. The dimple is positioned directly under the jet impingement nozzle. The Reynolds number ranges from 10,000 to 70,000, the dimple normalized depth is between 0 and 0.3, and the dimple normalized diameter varies from 1 to 2.5. The results for the flow field, target surface heat transfer, pin fin surface heat transfer, friction factor, and solid domain outer-wall temperature are included. For comparison, a Lamilloy cooling structure without the dimple is considered as the baseline. The results show that the dimple significantly increases the local heat transfer due to flow reattachment and recirculation. With an increase in the normalized dimple depth, the heat transfer on the target surface is first augmented due to the increase of flow reattachment and recirculation, and then it is decreased due to the large toroidal vortex. However, an increase in the dimple depth results in reduction of the pin fin surface heat transfer. As the dimple diameter increases, the target surface heat transfer is also first augmented due to the increase in the flow reattachment and recirculation, and then it is decreased as the flow separation increases. The thermal performance indicates that the intensity of the heat transfer enhancement depends on the depth and diameter of the dimple.
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| 2. |
- Chen, Xin, et al.
(författare)
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Reinforcement learning for distributed hybrid flowshop scheduling problem with variable task splitting towards mass personalized manufacturing
- 2024
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Ingår i: Journal of manufacturing systems. - : Elsevier BV. - 0278-6125 .- 1878-6642. ; 76, s. 188-206
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Tidskriftsartikel (refereegranskat)abstract
- Mass personalization manufacturing (MPM), an emerging production pattern, aims to improve enterprise profit in modern industries. However, the processing of heterogeneous orders from the consumers complicates such production scheduling problem. In addition, different scale tasks should adopt different splitting strategies in practical manufacturing, which makes the task splitting method more worthy of investigation. Towards MPM, this paper presents a distributed hybrid flowshop scheduling problem with variable task splitting (DHFSP-VTS) to minimize the makespan and total energy consumption simultaneously. Meanwhile, the VTS allows the tasks to be split into different sublots so they can save setup and transfer time. To solve these problems, we present an order modularization processing method that can categorize multiple types of orders into specific generation tasks, and a highly effective reinforcement learning-multiple objective evolutionary algorithm based on decomposition (RLMOEA/D) is designed. In RL-MOEA/D, there are three features: (1) three initial rules are used for initialization based on the current splitting scheme that can increase the diversity of solutions; (2) the reinforcement learning agent uses the Q-learning mechanism to dynamically select the scheme of task splitting as action; (3) a neighborhood search strategy improves the exploitation ability and expand the solution space. To verify the effectiveness of RL-MOEA/D, the MOEA/Ds based on four splitting schemes and four RL combined meta-heuristics are compared on 18 instances. The results show that RL-MOEA/D can obtain the best optimization and stability of all the other comparison algorithms. Therefore, it's a new technique to solve DHFSP with large-scale tasks, especially for the problem of MPM.
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| 3. |
- Kristan, Matej, et al.
(författare)
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The Visual Object Tracking VOT2015 challenge results
- 2015
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Ingår i: Proceedings 2015 IEEE International Conference on Computer Vision Workshops ICCVW 2015. - : IEEE. - 9780769557205 ; , s. 564-586
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge 2015, VOT2015, aims at comparing short-term single-object visual trackers that do not apply pre-learned models of object appearance. Results of 62 trackers are presented. The number of tested trackers makes VOT 2015 the largest benchmark on short-term tracking to date. For each participating tracker, a short description is provided in the appendix. Features of the VOT2015 challenge that go beyond its VOT2014 predecessor are: (i) a new VOT2015 dataset twice as large as in VOT2014 with full annotation of targets by rotated bounding boxes and per-frame attribute, (ii) extensions of the VOT2014 evaluation methodology by introduction of a new performance measure. The dataset, the evaluation kit as well as the results are publicly available at the challenge website(1).
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| 4. |
- Lei, Luo, et al.
(författare)
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A numerical investigation of dimple effects on internal heat transfer enhancement of a double wall cooling structure with jet impingement
- 2016
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Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 26:7, s. 2175-2197
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - The dimple is adopted into a double wall cooling structure which is widely used in hot gas components to increase the heat transfer effects with relatively low pressure drop penalty. The purpose of this paper is to study the effect of dimple depth and dimple diameter on the target surface heat transfer and the inlet to outlet friction factor. Design/methodology/approach - The study is carried out by using the numerical simulations. The impingement flow is directly impinging on the dimple and released from the film holes after passing the double wall chamber. The ratio between dimple depth and dimple diameter is varied from 0 to 0.4 and the ratio between dimple diameter and impingement hole diameter is ranging from 0.5 to 3. The Reynolds number is between 10,000 and 70,000. Results of the target surface Nusselt number, friction factor and flow structures are included. For convenience of comparison, the double wall cooling structure without the dimple is considered as the baseline. Findings - It is found that the dimple can effectively enhance the target surface heat transfer due to thinning of the flow boundary layer and flow reattachment as well as flow recirculation outside the dimple near the dimple rim especially for the large Re number condition. However, the stagnation point heat transfer is reduced. It is also found that for a large dimple depth or large dimple diameter, a salient heat transfer reduction occurs for the toroidal vortex. The thermal performance indicates that the intensity of the heat transfer enhancement depends upon the dimple depth and dimple diameter Originality/value - This is the first time to adopt a dimple into a double wall cooling structure. It suggests that the target surface heat transfer in a double wall cooling structure can be increased by the use of the dimple. However, the heat transfer characteristic is sensitive for the different dimple diameter and dimple depth which may result in a different flow behavior.
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| 5. |
- Lei, Luo, et al.
(författare)
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Endwall heat transfer and aerodynamic performance of bowed outlet guide vanes (OGVs) with on- and off-design conditions
- 2016
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 69:4, s. 352-368
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Tidskriftsartikel (refereegranskat)abstract
- In this study, numerical simulations are conducted to investigate the effects of bowed outlet guide vanes (OGVs) on endwall heat transfer and aerodynamic performance. Both on- and off-design conditions are studied. For bowed vanes, the bowed angle varies from 10 degrees to 40 degrees and the normalized bowed height ranges from 0.1 to 0.3. Results are included for Nusselt number distributions on the endwall, the energy losses, the yaw angles, and near-wall flow structures. For the convenience of comparison, the straight vane is also studied as a baseline. It is found that the bowed vanes can effectively reduce the endwall heat transfer. Among the tested parameters, a bowed angle of 40 degrees and a normalized bowed height of 0.3 provide the best-controlled heat transfer for both the on- and off-design conditions. However, the bowed vanes have different effects on the energy losses and the yaw angles depending on the operating conditions. For the on-design condition with the inlet angle of 30 degrees (the incidence angle is 0 degrees) and the off-design condition with the inlet angle of 0 degrees, the bowed vanes do not significantly increase the energy losses and yaw angles, whereas for the off-design condition with the inlet angle of -30 degrees, significant changes are observed.
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| 6. |
- Lei, Luo, et al.
(författare)
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Heat transfer and friction factor in a dimple-pin fin wedge duct with various dimple depth and converging angle
- 2016
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Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 26:6, s. 1954-1974
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - The dimple is adopted into a pin fin wedge duct which is widely used in modern gas turbine vane cooling structure trailing edge region. The purpose of this paper is to study the effects of dimple depth and duct converging angle on the endwall heat transfer and friction factor in this pin fin wedge duct. Design/methodology/approach - The study is carried out by using the numerical simulations. The diameter of dimples is the same as the pin fin diameter with an inline manner arrangement in relation to the pin fin. The ratio between dimple depth and dimple diameter is varied from 0 to 0.3 and the converging angle is ranging from 0° to 12.7°. The Reynolds number is between 10,000 and 50,000. Results of the endwall Nusselt number, friction factor, and flow structures are included. For convenience of comparison, the pin fin wedge duct with a converging angle of 12.7° without dimples is considered as the baseline. Findings - It is found that the dimples can effectively enhance the endwall heat transfer due to the impingement on the dimple surface, reattachment downstream the dimple and recirculation in front of the pin fin leading edge. By increasing the converging angle, the heat transfer is also increased but with a large friction factor penalty. In addition, the heat transfer enhancement for deep depth cases is 1.57 times higher than that of the low depth case. The thermal performance indicates that the intensity of heat transfer enhancement depends upon the dimple depth and converging angle. Originality/value - It suggests that the endwall heat transfer in a pin fin wedge duct can be increase by the adoption of dimples. The optimal dimple relative depth is 0.2 with low friction factor and high heat transfer performance.
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| 7. |
- Lei, Luo, et al.
(författare)
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Heat transfer and friction factor performance in a pin fin wedge duct with different dimple arrangements
- 2016
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 69:2, s. 209-226
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Tidskriftsartikel (refereegranskat)abstract
- In this study, numerical simulations are conducted to investigate the effects of dimple positions on the endwall heat transfer and friction factor in a pin fin wedge duct. The dimple diameter is the same as the pin fin diameter, while the ratio between dimple depth and dimple diameter is 0.2. Three different dimple positions are investigated (i.e., directly upstream of the pin fins, in a staggered manner relative to the pin fins, or in line with the pin fins. The Reynolds number ranges from 10,000 to 50,000. Results for endwall Nusselt number, friction factor, and flow structure are included. For convenience of comparison, the pin fin wedge duct without dimples is studied as baseline. It is found that dimples can effectively enhance endwall heat transfer. Among the tested parameters, the dimple position in line with the pin fins provides the best heat transfer enhancement, with low friction factor penalty. However, the various dimple positions have distinct effects on the friction factor depending on the flow structure near the dimple zone. For the first position, the friction factor is markedly increased due to flow impingement, recirculation, and mixing, while for the second and third positions, the friction factor is changed slightly due to different flow behaviors.
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| 8. |
- Luo, Lei, et al.
(författare)
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Effects of pin fin configurations on heat transfer and friction factor in an improved lamilloy cooling structure
- 2017
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Ingår i: Heat Transfer Research. - 1064-2285. ; 48:7, s. 657-679
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Tidskriftsartikel (refereegranskat)abstract
- In this study, numerical simulations are conducted to investigate the effects of pin fin location, pin fin diameter, and pin fin shape on the target and pin fin surfaces heat transfer as well as friction factor in an improved Lamilloy cooling structure. The pin fin normalized location is varied from 0.35 to 0.65 while the pin fin diameter is changing from 15 mm to 60 mm. Cone-shaped pin fins are introduced, and the root to roof diameter ratio of the cone-shaped pin fin is ranging from 0.5 to 2. The Reynolds number is between 10,000 and 50,000. Results of the target and pin fin surfaces Nu number, friction factor, and flow structures are included. For convenience of comparison, the Lamilloy cooling structure whose pin fin normalized location is 0.5 with a pin fin diameter of 30 mm is studied as the baseline. It was found that with increase of the pin fin normalized location, the heat transfer on the pin fin surfaces is gradually decreased while the friction factor shows a lower value as the pin fins are positioned either near the impingement center or the film holes. This trend is also found for increasing the pin fin diameter. In addition, the heat transfer on the pin fin surface is increased remarkably by using a coneshaped pin fin with a slight target surface heat transfer penalty. It was also found that by changing the pin fin location, pin fin diameter, and the pin fin shape, it may reach 7.6% higher values than the baseline thermal performance based on the target surface Nu number while it is 43.58% based on the pin fin surface.
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| 9. |
- Luo, Lei, et al.
(författare)
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Parametric influence on convective heat transfer for an outlet guide vane
- 2016
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 70:4, s. 331-346
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Tidskriftsartikel (refereegranskat)abstract
- Improved understanding of the impact of the operating conditions on the heat transfer and fluid flow behaviors of an outlet guide vane (OGV) is essential for accurate prediction of the lifetime of jet engines. In this article, the heat transfer characteristics of an OGV at various Reynolds numbers (Re), free stream turbulence levels, Mach number (Ma), and surface roughness are studied numerically. The Re is kept at 300,000 and 450,000, respectively, the free stream turbulence intensity ranges from 3.2% to 13%, and the turbulent length scale is varied from 1.2 to 11 mm. The Ma is selected as 0.06, 0.25, and 0.35, and the sandy grain roughness height is increased from the smooth wall level up to 160 µm. Mid-span pressure coefficient and Nu distributions are presented. Basically, the heat transfer patterns and pressure profiles are weak functions of the Re and Ma. Increasing the Re slightly moves the transition position upstream, while the Ma has no effect on the transition process. On the suction side, the transition is induced by flow separation and a bump is visible in the pressure profile. However, the turbulence intensity, turbulence length scale, and surface roughness levels have significant effects on the heat transfer and pressure distributions. On the suction side, the bump is invisible and the “separation-induced transition” is replaced by the “by pass transition”. It is also found that the transition position moves upstream as the turbulence intensity, length scale, and roughness level increase.
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| 10. |
- Wang, Chenglong, et al.
(författare)
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Experimental study of fluid flow and heat transfer of jet impingement in cross-flow with a vortex generator pair
- 2019
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 135, s. 935-949
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Tidskriftsartikel (refereegranskat)abstract
- The present paper investigates the fluid flow and heat transfer behaviors of jet impingement in cross-flow modified by a vortex generator pair (VGP). The velocity of the jet is kept at 12 m/s and that of the cross-flow is varied between 5 m/s and 8 m/s. The spacing between the jet and target surface is 4 times the jet diameter. Particle Image Velocimetry (PIV) and Liquid Crystal Thermography (LCT) are used to measure the flow field and heat transfer, respectively. The interaction of the cross-flow and jet produces various vortices, and the jet is shown to be deflected downstream by the cross-flow. The streamwise velocity of the jet increases with the cross-flow while the wall-normal velocity and turbulent kinetic energy are reduced close to the target wall. The overall effect is to decrease the impingement heat transfer. The presence of the vortex generator pair decreases the cross-flow momentum and induces the downwash flow upstream, which is favorable for the jet penetration. Thus the jet has higher impinging velocity towards the wall with elevated turbulent kinetic energy. This explains the heat transfer enhancement of the jet impingement in cross-flow due to the VGP. When the height of the VGP increases, the positive influence on the impingement becomes more evident. It demonstrates that the heat transfer on the target wall is dominated by the wall-normal velocity of the impingement and the turbulent kinetic energy, rather than the streamwise velocity along the cross-flow direction. The combined experimental results of the fluid flow and heat transfer can also be used for validating and improving numerical simulation methods.
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