Roughness effects on flow losses of a high-lift low-pressure turbine cascade

Xian Zeng,Jiahuan Cui,Jiaqi Luo

doi:10.1063/5.0075604

Xian Zeng, Jiahuan Cui + Show 1 more

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https://doi.org/10.1063/5.0075604

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Abstract

Laminar separation induced flow transition has been regarded as one main source of flow losses of low-pressure turbines (LPTs). The realistic roughness favors the reduction of flow losses as the separation bubble reduces and even disappears. In this paper, a detailed grid-independent study is first presented to verify and validate the numerical solutions by solving Reynolds-averaged Navier–Stokes and shear stress transport γ-Reθ̃ transition model equations for a typical high-lift LPT. The roughness elements with different heights (Ra) are uniformly imposed on the whole suction side. The effects of Ra on the flow separation and transition and, thus, flow losses are studied. The results demonstrate that there is one critical Ra value, below which the flow losses decrease, while above which the flow losses increase as Ra increases. The roughness allocations by imposing roughness elements on different blade portions of the suction side are also studied. The sensitivities of flow loss reduction to roughness allocation are evaluated and illustrated. Moreover, the effects of Reynolds numbers (Re) are investigated. As Re decreases, the critical Ra value increases and a more roughened blade is favorable for flow loss reduction. This study paves the way for finding a practicable flow control method reducing the flow losses by optimally allocating roughness on the blade of high-lift LPTs.

Highlights

The low pressure turbine (LPT), as the heaviest component in aero engines, takes up to one third of the total weight of the core engine
The variations in the kinetic energy loss coefficient (KELC) vs k+ are consistent with the current roughness impact theory,14 which says that the performance impact of roughness is not a single function of k+ but depends on the value of k+
The results demonstrate once more that the increased roughness intensifies the turbulent flow when k+ is within the full turbulent regime

Summary

Introduction

The low pressure turbine (LPT), as the heaviest component in aero engines, takes up to one third of the total weight of the core engine. High-lift blade design is one well-recognized method to reduce the weight, manufacturing cost, and fuel consumption of the engine.. High-lift blade design is one well-recognized method to reduce the weight, manufacturing cost, and fuel consumption of the engine.1 This design increases the aerodynamic load of each blade, leading to stronger adverse pressure gradients in the expansion section of LPTs. Under the condition of low Reynolds numbers (Re), the boundary layers are more sensitive to the pressure gradient.. Under the condition of low Reynolds numbers (Re), the boundary layers are more sensitive to the pressure gradient.2 This stronger adverse pressure gradient will increase the possibility of flow separation and transition in the boundary layer, resulting in higher profile loss. Since Stieger and Zhang had studied the flow control in LPTs, research on the influence of vortex generator jets and unsteady wakes on the boundary layer separation and transition has been rapidly carried out

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