Aero-thermal performance improvements of unshrouded turbines through management of tip leakage and injection flows

Gao, Jie; Zheng, Qun; Zhang, Zhengyi; Jiang, Yuting

doi:10.1016/j.energy.2014.03.060

Cited by 19 publications

(6 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Overall, the PTI design has the weakest outlet total pressure loss control that is because the injection mass flow rate is small. Based on the previous research results about the effects of tip injection, 26 it is favorable for the leakage flow control to increase the injection mass flow rate to a suitable value, and then to further reduce the vane-end leakage losses. Therefore, the cross-section of the vane injection channel should be large, and this requirement can be fulfilled by the multiple channel arrangements instead of a single injection channel.…”

Section: Resultsmentioning

confidence: 99%

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Gao

Wei

Liu

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part C:

Self Cite

View full text Add to dashboard Cite

Variable geometry turbine exists in small mobile gas turbines or some marine gas turbines to enhance the part-load performance. However, there are efficiency penalties associated with the vane partial gap, which is needed for the movement of variable vanes. This paper investigates the vane-end clearance leakage flow for a flat tip, a cavity tip, a winglet tip, a tip with passive injection, and a cavity-winglet tip to assess the possibility of minimizing vane-end clearance losses in a variable geometry turbine cascade. First, calculations were done at the test rig conditions for comparison with measured data, and they were used for validation of computational fluid dynamics model. Then, numerical calculations were done for turbine typical conditions. Specific flow structures of the various clearance designs of variable vanes are described, and then the effects of vane turning, including exit Mach numbers of 0.34, 0.44, and 0.54 as well as turning angles of –6°, 0°, and 6° on total pressure losses and outflow yaw angle for different vane tips are shown. In addition, the sensitivity of aerodynamic losses to vane tip gap height is evaluated. Results show that the strong interactions near the tip endwall region change the near-tip loading distribution significantly. With winglet and cavity-winglet tip designs, the loading distribution becomes very similar to the typical fixed vane, and the total loading is reduced, thus reducing the vane-end losses. Among the different vane tips presented, the cavity-winglet tip achieves the best aerodynamic performance, and the cavity tip has the lowest sensitivity to vane tip gap height. Overall, the cavity-winglet tip is found to be the best choice for variable vanes. The research results can provide useful reference for the vane design in a real high endwall-angle variable geometry turbine.

show abstract

Section: Resultsmentioning

confidence: 99%

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Gao

Wei

Liu

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part C:

Self Cite

View full text Add to dashboard Cite

show abstract

“…It also improves the under-turning of leakage flow, as presented in Refs. [30,31]. So tip leakage vortex gets smaller and loss in turbine passage is reduced [10,32].…”

Section: Introductionmentioning

confidence: 99%

Impact of Cooling Injection on Shock Wave Over a Flat Tip in High Pressure Turbine

Zeng

Jiang

et al. 2021

Journal of Turbomachinery

View full text Add to dashboard Cite

Cooling design of highly-loaded turbine blade tips is challenged by the scarcity of experimental data and the lack of physical understanding in cooling and over-tip leakage (OTL) interaction under transonic conditions. To address these issues, this paper carried out transient thermal measurements through infrared thermography on a transonic flat tip with and without cooling injection. Experimental data of Nusselt number and cooling effectiveness were obtained and compared with computational fluid dynamics results for numerical validation. Both experimental data and simulation results show that cooling injection drastically augments tip Nusselt number near pressure side which is upstream of ejection, and in areas around coolant holes. Moreover, a strikingly low Nusselt number stripe is observed downstream of cooling injection from one of the holes in aft portion of blade. The strip is directed transverse to local OTL streamline flowing from pressure to suction side and sprawls to adjacent coolant wakes. Further numerical analyses concluded that cooling injection changes tip aerodynamics and overtip shock wave structure fundamentally. Oblique shock waves across uncooled flat tip are replaced by a confined shock train downstream of cooling injection and between cooling holes, which is constituted by two shocks normal to local OTL flow coming from pressure side. Across the first shock, density and pressure increases abruptly, contributing to thickening of tip boundary layer and the plummet of skin friction on tip surface, which is responsible for the sharp decline of tip Nusselt number and therefore, formation of low heat transfer stripe downstream cooling injection.

show abstract

“…In addition, the two flow control methods were combined in order to a more effective improvement in the tip leakage flow. 16,17…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the two flow control methods were combined in order to a more effective improvement in the tip leakage flow. 16,17 Among them, the blade tip injection and casing injection both utilize the actuating effects of air injections by the dust-exhaust hole or the cooling hole in a turbine, and are considered to have a good engineering application value. 18 Compared with the blade tip injection, the casing injection can be a fresh effort in the active flow control of tip leakage flow in a turbine and has been verified to have the potential of improving the flow performance near the blade tip of turbine.…”

Section: Introductionmentioning

confidence: 99%

Effects of a sweeping jet actuator on aerodynamic performance in a linear turbine cascade with tip clearance

Chen

Meng

et al. 2019

Proceedings of the Institution of Mechanical Engineers, Part G:

View full text Add to dashboard Cite

Sweeping jet actuator as a fresh attempt has been applied in controlling flow separations and improving aerodynamic performances in a linear turbine cascade with tip clearance. In the present study, the oscillating jet process of sweeping jet actuator in the tip clearance was illustrated and a potential advantage from a system integration perspective was validated by an unsteady numerical study. The excitation frequencies and excitation modes were also investigated for achieving the further understanding of the mechanism of sweeping jet actuator for controlling flow separations. By using sweeping jet actuator, the flow separation near the upper endwall was delayed and the flow loss at the outlet of the cascade was reduced. For the optimal case, the time-averaged total pressure loss decreased by about 11.7% with the jet flow rate of only 0.35% of the inlet flow rate. In addition, it was found that there exists an optimum frequency to achieve the optimum controlling effects on the flow separations. Because of the blockage of tip leakage flow at the local gap by the high-momentum fluid from sweeping jet actuator, the controlling effects on the tip leakage vortex loss were better than that on the passage vortex loss. Through the use of four excitation modes in this study, the total pressure losses at the outlet were all reduced in different degrees. Under the present boundary conditions and working parameters, the unsteady controlling mode of sweeping jet actuator was found to perform much better than the other steady modes.

show abstract

Aero-thermal performance improvements of unshrouded turbines through management of tip leakage and injection flows

Cited by 19 publications

References 17 publications

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Impact of Cooling Injection on Shock Wave Over a Flat Tip in High Pressure Turbine

Effects of a sweeping jet actuator on aerodynamic performance in a linear turbine cascade with tip clearance

Contact Info

Product

Resources

About