| 1. |
- Du, Kun, et al.
(author)
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Effect of non-axisymmetric endwall contouring and swirling inlet flow on film cooling performance of turbine endwall
- 2024
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In: International Journal of Heat and Mass Transfer. - 0017-9310. ; 229
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Journal article (peer-reviewed)abstract
- Non-axisymmetric endwall contouring (NEC) is one of the verified approaches to suppress secondary flows and improve aerodynamic performance. However, the design of NEC brings significant challenges to the design of endwall cooling structures. Herein, a pressure-sensitive paint experimental approach was used to obtain the film cooling effectiveness of the NEC endwall with a purge slot in this study. Three NEC types were adopted: NEC (COS), NEC (SIN), and NEC (−SIN). In addition, lean premixed combustion technology was used to achieve lower levels of NOx emissions. The turbine inlet was characterized by high turbulence and strong swirling. The effects of different swirling angles (±10, ±20, and ±30°) and densities were further explored. Due to the NEC profiling changing the secondary flow near the endwall area, coolant from the purge slot was better attached to the slot exit position, leading to a significant increase in the size of the high-cooling-efficiency region. With the mass flow ratio (MFR) varying from 0.5 to 2%, the film cooling effectiveness of the flat and NEC endwalls had similar variation characteristics. When the MFR = 0.5%, the area-averaged cooling efficiencies of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could be improved by 2, 12.5, and 20%, respectively. Positive swirling and smaller negative swirling inflow could improve the film cooling effectiveness inside the channel. The case of SA = +20° had the best improvement, where the film cooling effectiveness of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could reach up to 29, 35, 36, and 34%, respectively. The NEC (−SIN) endwall was less sensitive to the effects of the swirling inflow.
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| 2. |
- Du, Kun, et al.
(author)
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Effects of Ribbed-Cavity Tip on the Blade Tip Aerothermal Performance in a High Pressure Turbine Stage
- 2023
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In: Journal of Thermal Science. - : Springer Science and Business Media LLC. - 1003-2169 .- 1993-033X. ; 32:2, s. 800-811
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Journal article (peer-reviewed)abstract
- For unshrouded blade tip, the high-temperature gas flows through the tip clearance by force of the lateral pressure difference. Thereby, the blade tip endures increasing thermal load. Furthermore, the conventional blade tip treatment cannot continuously provide protection for the deteriorating service environment. In the present study, aerothermal characteristics of the squealer blade tip with staggered ribs, partial squealer rim and different partial squealer rim thickness were investigated to explore the influences of ribbed-cavity tip on the tip heat transfer, leakage flow and turbine stage efficiency. The numerical results indicate that the ribbed-cavity tips are beneficial for the reduction of the blade tip thermal load and leakage flow. Among the present six blade tip designs, the minimal area-averaged heat transfer coefficient is obtained by the case with the staggered ribs and a deeper squealer rim, which is reduced by 31.41% relative to the squealer tip. Plus, the blade tip modification closer to leading edge or tip mid-chord region performs better than trailing edge in reducing the tip leakage flow.
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| 3. |
- Du, Kun, et al.
(author)
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Effects of the multicavity tip coolant injection on the blade tip and the over tip casing aerothermal performance in a high-pressure turbine cascade
- 2023
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In: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 84:4, s. 340-354
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Journal article (peer-reviewed)abstract
- In high performance gas turbine engines, the over tip leakage flow driven by the lateral pressure gradient is inevitably induced inside the blade tip gap in the high-pressure stage turbine due to the freestanding airfoil design methodology. To obtain an increasing level of thermal efficiency, the turbine inlet temperature is gradually increased in terms of the Brayton cycle. Hence, the blade tip and the over tip casing are subjected to high thermal load. In real turbine blade, cavity tips are widely used to decrease the over tip leakage flow and the thermal load on the blade tip and over tip casing. In the present study, the numerical simulations were conducted to investigate the effects of the multicavity coolant injection on the blade tip and the over tip casing aerothermal performance. Three-dimensional (3-D) Reynolds-averaged Navier–Stokes (RANS) equations and standard (Formula presented.) turbulence model were solved together in the simulations. The results indicate the ribs inside the tip cavity alter the distribution of film cooling efficiency by changing flow structure within the tip gap. Most of the coolant is limited in each little cavity owing to the blockage of ribs. Here, the swirling action of each cavity vortex results in the coolant providing a wider film cooling coverage. Therefore, the increase in film cooling effectiveness on the blade tip surface is more efficient than that of over-tip casing. The blade with four tip cavities film cooling (4CFC) obtains the largest area-averaged film cooling effectiveness, which is augmented by 14.3% in comparison with the case with a single tip cavity film cooling (1CFC).
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| 4. |
- Du, Kun, et al.
(author)
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Investigation of a nozzle guide vane cooling characteristic under one engine inoperative conditions
- 2024
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In: International Journal of Heat and Fluid Flow. - 0142-727X. ; 106
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Journal article (peer-reviewed)abstract
- The film cooling characteristics of turboshaft engine vanes were studied under one engine inoperative (OEI) conditions. Variations in the operating conditions caused tremendous changes in Reynolds number (Reg), turbulence intensity (Tu) and swirling inflow of the mainstream. Therefore, pressure-sensitive paint (PSP), as a promising measuring technique, was adopted for analyzing the impacts of Reg and Tu on the vane film cooling effectiveness. Furthermore, numerical methods were utilized to explore the film cooling effectiveness of vanes with two different hole shapes under various swirling inflow conditions. The results indicated that enhancement in either Tu or the swirling inflow decreased the film cooling effectiveness. However, Reg had little effect on the film cooling performance within the studied range. The area-averaged film cooling effectiveness decreased by 5.6% when Tu increased from 15% to 30%. In addition, the vane film cooling performance was greatly impacted by swirling inflow. The film cooling effectiveness exhibited continuous decreases as the swirling angle (SA) increased, especially for the vane with shaped holes; its maximum area-averaged film cooling effectiveness reduction was 28.9%. Overall, OEI conditions mainly altered the Tu and swirling inflow, thus changing the aerothermal performance, while Reg remained relatively unchanged in this research. The present research aimed to contribute to designing the turbine cooling under OEI conditions.
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| 5. |
- Du, Kun, et al.
(author)
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Non-axisymmetric Endwall film cooling characteristics considering the influences of cylindrical holes and laidback fan-shaped holes
- 2024
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In: International Journal of Heat and Mass Transfer. - 0017-9310. ; 225
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Journal article (peer-reviewed)abstract
- Flow fields near the turbine vane endwall are complicated due to the endwall cross flows. The use of a non-axisymmetric endwall is regarded as an efficient technique to reduce the lateral pressure difference, decreasing the endwall cross flow. Numerical analysis was performed to determine how the non-axisymmetric endwall affected the vortex structure and heat transfer level. The cooling performance was investigated with cylindrical and laidback fan-shaped holes (7–7–7), which were arranged in rows aligned in the axial direction. The results showed that the non-axisymmetric endwall could significantly reduce the circumferential pressure difference and suppress the growth of the passage vortex, and the area-averaged heat transfer coefficient was reduced by 3.34%. The outlet area of the film hole was altered by the non-axisymmetric endwall, and the over-cooled regions may have appeared as a result of the excessive area increase. The influence of the non-axisymmetric endwall was concentrated at 0.4 < Z/Cax < 1.0 for the cylindrical hole. With the increase in M, the film cooling effectiveness of the non-axisymmetric endwall attained a higher level than that of the flat endwall. For the laidback fan-shaped hole, the effect of the non-axisymmetric endwall was confined within 0.25 < Z/Cax < 1.0. The half-period trigonometric function of the non-axisymmetric endwall (HTFN) achieved the optimal cooling performance for three blowing ratios. However, the periodic trigonometric function of the non-axisymmetric endwall (PTFN) only outperformed the flat endwall when M= 1.5.
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| 6. |
- Du, Kun, et al.
(author)
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Numerical Investigation on Flow and Cooling Characteristics of a Micro-Ribbed Vane Endwall
- 2023
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In: Journal of Thermal Science. - : Springer Science and Business Media LLC. - 1003-2169 .- 1993-033X. ; 32:2, s. 786-799
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Journal article (peer-reviewed)abstract
- The secondary flow originated from the inherent pressure gradient inside the vane cascade has a strong impact on the endwall cooling performance as the crossflow sweeps the upstream coolant jet towards the suction side, resulting in intensifying thermal load near the pressure side endwall. Hence a novel ribbed-endwall is introduced to suppress passage crossflow. The effects of the mass flow ratio and the rib layout were examined using numerical simulations by solving the three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) k-ω turbulence model. The results indicate that the ribs effectively prevent the coolant migrating from the pressure side to the suction side, helping the coolant jet to spread along the lateral orientation. Therefore, the endwall adiabatic film cooling effectiveness is substantially improved. The maximum cooling effectiveness is achieved for the case with three-ribs when the height of the rib equals one hole diameter among all cases. The area-averaged adiabatic cooling effectiveness is enhanced by 31.6% relative to the flat endwall when the mass flow ratio of coolant to mainstream equals to 0.52%. More importantly, the ribbed-endwall obtains a relatively lower level of aerodynamic loss owing to the reduced lateral migration inside the vane cascade.
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