Effect of Endwall Boundary Layer Thickness on Losses in a LPT Cascade With Unsteady Wakes

Volume 2B: Turbomachinery

2016

The secondary flow increases the loss and changes the flow incidence in the downstream blade row. To prevent hot gases from entering disk cavities, purge flows are injected into the mainstream in a real aero-engine. The interaction between purge flows and the mainstream usually induces aerodynamic losses.The endwall loss is also affected by shedding wakes and secondary flow from upstream rows. Using a series of eddy-resolving simulations, this paper aims to improve the understanding of the interaction between purge flows, incoming secondary flows along with shedding wakes and mainstream flows on the endwall within a stator passage.It is found that for a blade with an aspect ratio of 2.2, a purge flow with a 1% leakage rate increases loss generation within the blade passage by around 10%. The incoming wakes and secondary flows increase the loss generation further by around 20%. The purge flow pushes the passage vortex further away from the endwall and increases the exit flow angle deviation. However, the maximum exit flow angle deviation is reduced after introducing incoming wakes and secondary flows. The loss generation rate is calculated using the mean flow kinetic energy equation. Two regions with high loss generation rate are identified within the blade passage: the corner region and the region where passage vortex interacts with the boundary layer on the suction surface.Loss generation rate increases dramatically after the separated boundary layer transitions. Since the endwall flow energizes the boundary layer and triggers TURBO-16-1142 Cui 2 earlier transition on the suction surface, the loss generation rate close to the endwall at the trailing edge is suppressed.

Section: Resultsmentioning

confidence: 97%

Numerical Study of Purge and Secondary Flows in a Low Pressure Turbine

Volume 2B: Turbomachinery

2016

“…Effect of inflow conditions : de la Blanco et al (2003) reported that the state of the incoming endwall boundary layer plays an important role in endwall loss generation. By simulating the wakes using upstream moving bars, Steurer et al (2014) studied the effects of incoming wakes on the secondary flow. The effect of secondary flow from the upstream blade row was not considered in this study.…”

Section: Othersmentioning

confidence: 99%

Numerical investigation of secondary flows in a high-lift low pressure turbine

Rao

International Journal of Heat and Fluid Flow

2017

a b s t r a c tIn turbomachines, secondary flows (or endwall flows) typically originate at the junction between endwalls and the blade surface. Within the blade passage, the strength of the secondary flows is amplified by the crossflow from the pressure to the suction surface of the blade. The enhanced mixing due to secondary flows induce additional losses into the system. This decreases the overall work output and also changes the flow incidence onto the downstream blade rows. Using a series of high-fidelity eddy resolving simulations, the current study attempts to provide an improved understanding for the complex flow physics over the endwalls of a high-lift Low Pressure Turbine (LPT) blade. The effect of three different inflow conditions has been studied. These include a laminar boundary layer (LBL), a turbulent boundary layer (TBL) and wakes with secondary flow (W&S) from an upstream blade row. For the simulations with TBL and W&S, precursor eddy resolving simulations were used to prescribe realistic inflows. The loss generation mechanisms were subsequently studied both at the endwall and the midspan, which includes evaluating the mass-averaged total pressure loss coefficient ( Y p ) and the loss generation rate.When compared to LBL, additional disturbances from an incoming TBL and wakes with secondary flows enhanced the mixing within the blade passage resulting in a substantial increase in the total pressure loss. Prior to flow transition, incoming wakes with secondary flows increased the local loss generation rate at both the endwall and the midspan in the front portion of the blade passage ( x / C x < 0.84). In contrast, in the aft portion of the passage ( x / C x > 0.8), the incoming wakes effectively suppressed the separation bubble at the midspan thereby decreasing the local loss generation rate. It is also demonstrated that the wakes shed from the trailing edge at the mid-span mix out rapidly when compared to the passage vortex at the endwall.

“…The objectives of these studies can be broadly classified into understanding the: a) endwall flow features, b) loss generation mechanisms and c) effect of inflow conditions. A brief 15 review of the relevant literature is given below:…”

Section: Introductionmentioning

confidence: 99%

“…Effect of inflow conditions: Blanco et al [14] reported that the state of the in-40 coming endwall boundary layer plays an important role in endwall loss generation. By simulating the wakes using upstream moving bars, Steurer [15] studied the effects of incoming wakes on the secondary flow. The effect of secondary flow from the upstream blade row was not considered in this study.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Numerical investigation of secondary flows in a high-lift low pressure turbine

Rao

Proceeding of THMT-15. Proceedings of the Eighth International Symposium on Turbulence Heat and Mass Transfer

2015

In turbomachines, secondary flows (or endwall flows) typically originate at the junction between endwalls and the blade surface. Within the blade passage, the strength of the secondary flows is amplified by the crossflow from the pressure to the suction surface of the blade. The enhanced mixing due to secondary flows induce additional losses into the system. This decreases the overall work output and also changes the flow incidence onto the downstream blade rows. Using a series of high-fidelity eddy resolving simulations, the current study attempts to provide an improved understanding for the complex flow physics over the endwalls of a high-lift Low Pressure Turbine (LPT) blade. The effect of three different inflow conditions has been studied. These include a laminar boundary layer (LBL), a turbulent boundary layer (TBL) and wakes with secondary flow (W&S) from an upstream blade row. For the simulations with TBL and W&S, precursor eddy resolving simulations were used to prescribe realistic inflows. The loss generation mechanisms were subsequently studied both at the endwall and the midspan, which includes evaluating the mass-averaged total pressure loss coefficient (Y p ) and the loss generation rate.When compared to LBL, additional disturbances from an incoming TBL and wakes with secondary flows enhanced the mixing within the blade passage resulting in a substantial increase in the total pressure loss. Prior to flow transition, incoming wakes with secondary flows increased the local loss generation rate at both the endwall and the midspan in the front portion of the blade passage (x/C x < 0.84). In contrast, in the * Corresponding author aft portion of the passage (x/C x > 0.8), the incoming wakes effectively suppressed the separation bubble at the midspan thereby decreasing the local loss generation rate.It is also demonstrated that the wakes shed from the trailing edge at the mid-span mix out rapidly when compared to the passage vortex at the endwall.