Effects of periodic wakes on the endwall secondary flow in high-lift low-pressure turbine cascades at low Reynolds numbers

2017 ◽  
Vol 233 (1) ◽  
pp. 354-368 ◽  
Author(s):  
Xiao Qu ◽  
Yanfeng Zhang ◽  
Xingen Lu ◽  
Ge Han ◽  
Ziliang Li ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
High Reynolds

Periodic wakes affect not only the surface boundary layer characteristics of low-pressure turbine blades and profile losses but also the vortex structures of the secondary flow and the corresponding losses. Thus, understanding the physical mechanisms of unsteady interactions and the potential to eliminate secondary losses is becoming increasingly important for improving the performance of high-lift low-pressure turbines. However, few studies have focused on the unsteady interaction mechanism between periodic wakes and endwall secondary flow in low-pressure turbines. This paper verified the accuracy of computational fluid dynamics by comparing experimental results and those of the numerical predictions by taking a high-lift low-pressure turbine cascade as the research object. Discussion was focused on the interaction mechanisms between the upstream wakes and secondary flow within the high-lift low-pressure turbine. The results indicated that upstream wakes have both positive and negative effects on the endwall flow, where the periodic wakes can decrease significantly the size of the separation bubble, prevent the formation of secondary vorticity structures at relatively high Reynolds numbers (100,000 and 150,000), and reduce the cross-passage pressure gradient of cascade. In addition, periodic wakes can improve the cascade incidence characteristic in terms of reducing the overturning and underturning of the secondary flow at downstream of the cascade all of which are beneficial for decreasing the endwall secondary losses, whereas more endwall boundary layer is involved in the main flow passage due to the wake transport, resulting in increased strength of the secondary flow at low Reynolds number of 25,000 and 50,000. Compared with the results without wakes, the total pressure loss for unsteady condition at the cascade exit decreases by 2.7% and 6.1% at high Reynolds number of 100,000 and 150,000, respectively. However, the secondary loss at unsteady flow conditions increases at low Reynolds number of 25,000 and 50,000.

The Influence of Mach Number on the Boundary Layer Development of High-Lift Low Pressure Turbine in Low Reynolds Number

2020 ◽  
Author(s):  
Wenhua Duan ◽  
Jian Liu ◽  
Weiyang Qiao
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Turbine Blade ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Layer Development

Abstract A numerical analysis of the effect of Mach number on the boundary layer development and aerodynamic performance of a high-lift, after loaded low pressure turbine blade is presented in this paper. The turbine blade is designed for the GTF engine and works in a low Reynolds number, high Mach number environment. Three different isentropic exit Mach numbers (0.14, 0.87 and 1.17) are simulated by large eddy simulation method, while the Reynolds number based on the axial chord length of the blade and the exit flow velocity is kept the same (1 × 105). The condition Mais,2 = 0.14 represents the lowspeeed wind tunnel environment which is usually used in the low pressure turbine investigation. The condition Mais,2 = 0.87 represents the design point of the turbine blade. The condition Mais,2 = 1.17 represents the severe environment when the shock wave shows up. A comparison of the boundary layer development is made and the total pressure loss results from the boundary layer is discussed.

Unsteady Loss Production Mechanisms in Low Reynolds Number, High Lift, Low Pressure Turbine Profiles

2007 ◽  
Author(s):  
Benigno J. Lazaro ◽  
Ezequiel Gonzalez ◽  
Raul Vazquez
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Suction Side ◽  
Low Pressure ◽  
Momentum Thickness ◽  
High Lift ◽  
Recirculation Bubble ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
Production Mechanisms

The loss production mechanisms that occur in modern high lift, low pressure turbine profiles operating at low Reynolds numbers and subjected to periodic incoming wakes generated by an upstream located, moving bars mechanism, have been experimentally investigated. In particular, laser-Doppler and hot-wire anemometry have been used to obtain spatially and temporally resolved characterizations of the suction side boundary layer structure at the profile trailing edge. Phase measurements locked to the motion of the upstream moving bars have been used to analyze the effect of the incoming wakes on the suction side boundary layer response, which accounts for most of the profile loss generation. It is observed that the incoming wakes produce a temporal modulation of the boundary layer momentum thickness. This modulation appears to be connected to shedding of rotational flow from the recirculation bubble that develops in the suction side of high lift, low pressure turbine profiles. Furthermore, the momentum thickness reduction and subsequent increase that occurs after the wake passage appears to be related to the unsteady process leading to the recovery of the suction side recirculation bubble. The effect of the wake passage frequency and back surface adverse pressure gradient on the above described mechanisms is also investigated. Conclusions obtained can help understanding the unsteady response of modern low pressure turbine profiles operating in the low Reynolds number regime.

Unsteady flow mechanism of the integrated aggressive inter-turbine duct in low Reynolds number condition

2020 ◽  
Vol 234 (9) ◽  
pp. 1507-1517
Author(s):  
Hongrui Liu ◽  
Jun Liu ◽  
Qiang Du ◽  
Guang Liu ◽  
Pei Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Low Reynolds

Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.

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