| 1. |
- Wang, Jin, et al.
(författare)
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Conjugated heat transfer analysis of a film cooling passage with turbulator ribs
- 2016
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Ingår i: Heat Transfer Research. - 1064-2285. ; 47:2, s. 89-103
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the adiabatic film cooling effectiveness and conjugate heat transfer characteristics for a circular hole are investigated numerically. Seven turbulator ribs are located on the internal wall, and a film cooling hole between two adjacent ribs has an inclination angle of 30°. The secondary flow rate is affected by the internal channel flow velocity, and the external film cooling is combined with the internal channel flow conditions. In the conjugate heat transfer research, two different plate materials are considered to analyze the heat conduction characteristics. The results show that the turbulator ribs enhance the downstream heat transfer and provide a more extensive coverage area and effective cooling protection. More blade-wall heat is transferred by heat conduction, which makes the area-average wall temperature for the high thermal conductivity case to decrease along the secondary flow direction. The wall temperature distribution and film cooling effectiveness are affected significantly by heat conduction.
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| 2. |
- Wang, Jinsheng, et al.
(författare)
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Conjugated heat transfer investigation with racetrack-shaped jet hole and double swirling chamber in rotating jet impingement
- 2018
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 73:11, s. 768-787
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study is performed to investigate the effects of jet hole shape and channel geometry on impingement cooling for both stationary and rotating condition. Two hole shapes and two channel geometries are introduced to counteract the adverse effects of centrifugal force and Coriolis force which are induced by rotation. Both the fluid and solid part are considered for realizing the conjugate heat transfer simulation. The unsteady k-ω SST turbulence model was employed to obtain the time-averaged Nusselt number distributions, time-averaged temperature and temperature gradient fields and the turbulent flow structure. The results show that the cooling jet from the racetrack-shaped hole can effectively withstand the intensive streamwise crossflow to enhance the heat transfer. The double swirling chamber (DSC) channel significantly improves the heat transfer characteristics on the cambered surface and diminishes the adverse effects of the Coriolis force. The high Nu number region is expanded while the temperature uniformity is improved. The combination of the racetrack-shaped hole and DSC channel provides the highest heat transfer among the four cases. The averaged Nu numbers on both the leading and trailing sides for all tested cases show obvious downtrend as rotation number increases, especially at high Reynolds number.
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| 3. |
- Wang, Jinsheng, et al.
(författare)
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Numerical investigation of heat transfer and fluid flow in a rotating rectangular channel with variously-shaped discrete ribs
- 2018
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 129, s. 1369-1381
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study is performed to investigate the effects of various discrete rib configurations on the heat transfer and fluid flow characteristics of a rotating rectangular straight channel (aspect ratio of 2:1) with 45° orientation. Three parameters of the discrete rib configuration - rib streamwise distance, rib widthwise distance, and inner-half-rib angle - are examined based on a continuous inclined rib. The blockage ratio (e/Dh) is 0.1 and the pitch ratio (P/e) is 10. The Reynolds number is fixed at 10,000 in each case, while the rotation number is varied from 0 to 0.7. Details of the turbulent flow structure, turbulence kinetic energies, temperature fields, normalized Nusselt numbers, friction penalties and thermal performance factors were obtained by Computation of Fluid Dynamics (CFD) with the k-ω SST turbulence model. The results show that a small streamwise rib gap can effectively enhance the leading wall heat transfer. The heat transfer decreases gradually as the streamwise rib gap is enlarged. The inner-half-rib angle β provides the most conspicuous effects on heat transfer and friction loss, and the best heat transfer appears at β = 60° or 75° for different rotating conditions. The case with a rib streamwise gap normalized distance of 0.2 and inner-half-rib angle of 45° provides best thermal performance. A widthwise rib gap is favorable in reducing pressure drop, but its heat transfer augmentation is limited.
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| 4. |
- Liu, Jian, et al.
(författare)
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Application of fractal theory in the arrangement of truncated ribs in a rectangular cooling channel (4 : 1) of a turbine blade
- 2018
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 139, s. 488-505
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Tidskriftsartikel (refereegranskat)abstract
- Ribs are widely employed in internal cooling passages of turbine blades and other heat transfer equipment to enhance heat transfer by making cooling air flow through internal ribbed passages. From mathematics, a fractal is an abstract object used to simulate naturally occurring objects, which exhibits similar patterns and properties also at smaller scales. The evolving fractal structures of the continuous ribbed channels contains two sides truncated ribs, three sides truncated ribs, five sides truncated ribs and nine sides truncated ribs. The thermal performance of the ribbed channels is compared by taking both heat transfer and pressure drop into consideration. Steady Liquid Crystal Thermography (LCT) is employed to measure surface temperature and derive heat transfer coefficients over the ribbed surfaces in the tested channels. Turbulent flow details are presented by numerical calculations with an established turbulence model, i.e. the k-ω SST model. From the experimental results, it is found that fractal truncated ribs with smaller length scales have larger heat transfer at the low Reynolds numbers. On the other hand, the difference of Nusselt numbers for different cases can be negligible at the high Reynolds numbers. Generally, fractal truncated ribs with smaller length scales have a more uniform heat transfer distribution. The correlation between Nusselt number and Reynolds number are respectively Re0.69, Re0.64 and Re0.61 for case 2 (Two Sides Truncated ribs), case 3 (Three Sides Truncated Ribs) and case 4 (Five Sides Truncated Ribs). The distribution of the high Nusselt number regions is kept identical during the fractal truncated ribs evolving process, which is also valid for the flow field.
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| 5. |
- Liu, Jian, et al.
(författare)
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Effect of the relative location of a pocket cavity on heat transfer and flow structures of the downstream endwall with a symmetrical vane
- 2019
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 145
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Tidskriftsartikel (refereegranskat)abstract
- In a gas turbine engine, the low pressure turbine (LPT) and the outlet guide vane (OGV) part are connected in the rear part. The outlet nozzle is designed as a contracted part to increase the ejection velocity and a pocket cavity (PC) is formed at this location. In this research work, the effects of the locations of the PC on the downstream endwall with a symmetrical vane (SV) are investigated and evaluated. The PC is simplified as a triangular groove with a small fillet radius on the pocket edge connecting to the flat surface. The distance ratio (Ld/D) between the PC and the SV is ranging from 1.0 to 3.0 and the case with only the SV is also considered. Heat transfer and flow field characteristics over the tested surfaces are provided. Heat transfer coefficients (HTCs) are measured by steady-state Liquid Crystal Thermography (LCT) with Reynolds number (Re) ranging between 87.6 × 103 and 21.9 × 103. Two kinds of turbulence models are used to close the N-S equations for the present flow field, i.e., the unsteady DES simulation and the steady the k-ω SST model. When the PC is placed upstream of the SV, the higher Nu regions around the SV due to the horse-shoe vortices is significantly decreased compared with the SV only case. With the distance ratio between SV and PC becoming larger, the weakening effect of the PC is greatly reduced and the heat transfer distributions around the SV on the endwall are seen to approach those of the SV only case (Case 0) when the distance ratio is extremely large. The PC changes the pattern of flow impingement on the SV and the ejection flow from the PC is greatly enhanced. The ejection flow interacts with the mainstream flow and the flow separates from the endwall when it is approaching the SV. Then, the higher heat transfer around the SV is weakened.
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| 6. |
- Liu, Jian, et al.
(författare)
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Effects of the pocket cavity on heat transfer and fluid flow of the downstream outlet guide vane at different flow attacking angles
- 2018
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 74:3, s. 1087-1104
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Tidskriftsartikel (refereegranskat)abstract
- A pocket cavity is generated at the junction position of the low pressure turbine (LPT) and the outlet guide vane (OGV) in the rear part of a modern gas turbine jet engine. In the present study, a triangular pocket cavity is placed upstream of an OGV at different distances. The effects of the pocket cavity on heat transfer and fluid flow of the downstream OGV with different flow attack angles are investigated numerically with well validated turbulence models. The flow attack angles are varied as –30°, 0°, and +30° at a constant Reynolds number =160,000. The turbulent flow details are provided by numerical calculations using two turbulence models, the unsteady DES model and the steady k-ω SST model. For different flow attack angles, the high Nusselt number regions around the OGV are changed. The high heat transfer region is really drawn back at a flow attack angle = +30° (Case 2b) compared with Case 2a with a flow attack angle =0°. As the flow attack angle is changed to –30° (Case 2c), the high Nusselt number regions are greatly enlarged not only on the suction side also on the pressure side because of the strengthened flow impingement on the vane surfaces. The pocket cavity weakens the flow impingement on the vane surfaces and the effect is more obvious when the pocket cavity is placed close to the vane. In addition, the heat transfer distribution over the pocket surface is also affected by the location of the vane. When the vane is placed close to the pocket cavity (Case 1), the heat transfer on the pocket edge is increased. In the case with a flow attack angle =0°, the high turbulent kinetic energy region is mainly located near the vane and wake region downstream the vane and recirculating flows can hardly be found.
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| 7. |
- Liu, Jian, et al.
(författare)
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Heat transfer enhancement and turbulent flow in a high aspect ratio channel (4:1) with ribs of various truncation types and arrangements
- 2018
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 123, s. 99-116
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Tidskriftsartikel (refereegranskat)abstract
- Ribs are often employed in internal cooling passages of turbine blades to augment heat transfer with cooling air flowing through the internal ribbed passages. The present work concentrates on truncated ribs to improve thermal performances with continuous ribs in a high aspect ratio channel. With various truncation types and arrangements of truncated ribs, the optimized thermal performance of ribbed channels is attempted for by taking both heat transfer and pressure drop into consideration. Eight different ribbed channels with various truncation types and arrangements are investigated. Liquid Crystal Thermography (LCT) is employed to measure surface temperature and derive heat transfer coefficients over the ribbed surfaces in the tested channels. The turbulent flow details are presented by numerical calculations with an established turbulence model, i.e. the k-ω SST. From the obtained results, it is found that truncated ribs can reduce the pressure loss penalty without reducing the heat transfer enhancement in the tested channels. By changing the configurations to staggered arrangements, the heat transfer can be further enhanced associated with a moderate pressure drop. The truncated ribs generate transverse vortices at the truncation gaps and reduce the recirculating flow behind the ribs. Enhanced flow mixing contributes to the increased heat transfer. By the staggered arrangement, the flow path becomes more complex and the flow mixing is further enhanced. Truncated ribs are promising for applications in the high aspect ratio channel of the turbine blades and the enhancement factor is about 10%.
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| 8. |
- Liu, Jian, et al.
(författare)
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Heat transfer enhancement and turbulent flow in a rectangular channel using perforated ribs with inclined holes
- 2019
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Ingår i: Journal of Heat Transfer. - : ASME International. - 0022-1481 .- 1528-8943. ; 141:4
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Tidskriftsartikel (refereegranskat)abstract
- In internal cooling passages in a turbine blade, rib structures are widely applied to augment convective heat transfer by the coolant passing through over the ribbed surfaces. This study concentrates on perforated 90 deg ribs with inclined holes in a cooling duct with rectangular cross section, aiming at improving the perforated holes with additional secondary flows caused by inclined hole arrangements. Two sets of perforated ribs are used in the experiments with the inclined angle of the holes changing from 0 deg to 45 deg and the cross section are, respectively, circular and square. Steady-state liquid crystal thermography (LCT) is applied to measure the ribbed surface temperature and obtain corresponding convective heat transfer coefficients (HTCs). Two turbulence models, i.e., the k-ω shear stress transportation (SST) model and the detached eddy simulation (DES) model, are used in the numerical studies to simulate the flow fields. All the inclined cases have slightly larger overall averaged Nusselt number (Nu) than with straight cases. The enhancement ratio is approximately 1.85-4.94%. The averaged Nu in the half portion against the inclined direction is enlarged for the inclined hole cases. The inclined hole cases usually have smaller averaged Nu in the half portion along the inclined direction. For the straight hole case and small inclined angle case, the penetrated flows mix with the mainstream flows at the perforated regions. When the inclined angle is larger, the penetrated flows are pushed to the inclined direction and mixing with the approaching flows occurs just at the side of the inclined direction.
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| 9. |
- Liu, Jian, et al.
(författare)
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Investigation of heat transfer and fluid flow over pocket cavity in the rear part of gas turbine
- 2016
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Ingår i: Heat Transfer and Thermal Engineering. - 9780791850626 ; 8
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Konferensbidrag (refereegranskat)abstract
- The pocket cavity is generated at the transition part between the low pressure turbine (LPT) and outlet guide vane (OGV) in a gas turbine engine. Because the important connection with OGV, the heat transfer and fluid flow need to be investigated and analyzed. In the present work, a simplified triangular pocket cavity is built and heat transfer and fluid flow are investigated experimentally and numerically. Liquid Crystal Thermography (LCT) is employed to measure the heat transfer over the pocket surface with Reynolds number ranging from 54,054 to 135,135. In addition, two fillets with different radii are designed to investigate the flow structures over the pocket surface. The turbulent flow details are provided by numerically calculations based on the commercial software Fluent 15.0 with a validated turbulence model. Based on the results, the highest heat transfer value is located in the downstream boundary of the pocket cavity where the strongest flow impingement happens. The smaller fillet radius presents a higher heat transfer peak value and also induces stronger recirculating flow inside the pocket cavity. Considering the design requirement in the rear part of a gas turbine, i.e., to decrease the heat transfer peak value, a larger fillet radius is recommended for practical design. The heat transfer and flow details also provide a reliable reference for gas turbine engine design.
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| 10. |
- Wang, Jingyu, et al.
(författare)
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A network model and numerical simulations of flow distributions in packed bed reactors with different packing structures
- 2020
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 172
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Tidskriftsartikel (refereegranskat)abstract
- Due to the high specific surface area, packed bed reactors are widely used in real engineering applications. The flow distribution, which is highly dependent on the packing structure, can be vital for the heat/mass transfer and reaction performances. This makes the study of the flow distribution in packed beds quite important. In the present paper, an equivalent network model based on the Voronoi tessellation is proposed to predict the flow field. In addition, a relationship between the hydraulic resistance and the pore structure is introduced. Besides, the influence of the packing structure on the flow distribution is discussed. Numerical simulations using ANSYS FLUENT are also carried out to check the reliability of the network model. It is found that firstly, the proposed correlation of hydraulic resistance can capture the flow characteristics with high accuracy and the flow distributions predicted by the network model fit well with the simulation results for 2-D ordered packing structures with mono-sized and dual-sized particles and disordered packing structures with mono-sized particles. Secondly, it is revealed that, the packing form and the pore dimension have a significant effect on the flow distribution. Thirdly, the flow rate in a certain channel is dependent on the hydraulic resistances of the adjacent channels rather than just on itself.
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