Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows

Blanco, E. Rosa de la; Hodson, H. P.; Vázquez, Raúl; Torre, Diego de la

doi:10.1243/095765003322315496

Cited by 19 publications

(13 citation statements)

References 10 publications

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“…As shown in figure 17 at x/C x = 0.5, the passage vortex loss core meets 9 The loss generation rate of term VI is mainly from boundary layers where mean flow velocity gradient is high. Due to its relatively simpler mechanism, the contour of term VI is not given here.…”

Section: Resultsmentioning

confidence: 86%

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

Cui

Tucker

2016

Volume 2B: Turbomachinery

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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.

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Section: Resultsmentioning

confidence: 86%

“…Mean boundary layer velocity profile on the endwall at the inlet compared with the measurements[9].denotes the quantities at the inlet. After scaling, a method based on velocity triangles[10] was used to rotate the velocity vector to ensure the same pressuredistribution at the midspan as the other cases.…”

mentioning

confidence: 99%

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

Cui

Tucker

2016

Volume 2B: Turbomachinery

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“…To assess the accuracy of the CFD, calculations are performed for experimental cascade studies (Hodson and Dominy, 1987;Gregory-Smith et al, 1988;de la Rosa Blanco et al, 2003). Figure 2 compares measured and calculated endwall total pressure loss coefficients; the average error is less than 10%, which is deemed to be acceptable.…”

Section: Meshing and Cfdmentioning

confidence: 99%

“…Hodson and Dominy, 1987), but there are some notable exceptions. For example, de la Rosa Blanco et al (2003) examined two low pressure turbine blades with identical flow angles but different blade thickness. Increasing the size of the turbulent inlet boundary layer, they found that the endwall loss increased for both blades but more rapidly for the thinner blade.…”

Section: Introductionmentioning

confidence: 99%

The sensitivity of turbine cascade endwall loss to inlet boundary layer thickness

Coull

Clark

Vázquez

2019

J. Glob. Power Propuls. Soc.

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The development of hub and casing boundary layers through a turbomachine is difficult to predict, giving rise to uncertainty in the boundary conditions experienced by each blade row. Previous studies in turbine cascades disagree on the sensitivity of endwall loss to such inlet conditions. This paper explores the problem computationally, by examining a large number of turbine cascades and varying the inlet boundary layer thickness. It is demonstrated that the sensitivity of endwall loss to inlet conditions is design dependent, and determined by the component of endwall loss associated with the secondary flow. This Secondary-Flow-Induced loss is characterised by a vorticity factor based on classical secondary flow theory. Designs that produce high levels of secondary vorticity tend to generate more loss and are more sensitive to inlet conditions. This sensitivity is largely driven by the dissipation of Secondary Kinetic Energy (SKE): thickening the inlet boundary layer causes the secondary vorticity at the cascade exit to be more dispersed within the passage, resulting in larger secondary flow structures with higher SKE. The effects are captured using a simple streamfunction model based on classical secondary flow theory, which has potential for preliminary design and sensitivity assessment.

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“…Due to the limitation of accessibility within the blade passage, only measurements downstream of the trailing edge were reported in MacIsaac et al (2012) . 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.…”

Section: Othersmentioning

confidence: 99%

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

Cui

Rao

Tucker

2017

International Journal of Heat and Fluid Flow

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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.

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Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows

Cited by 19 publications

References 10 publications

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

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

The sensitivity of turbine cascade endwall loss to inlet boundary layer thickness

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

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