Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling

Ingram, Grant; Gregory-Smith, D. G.; Harvey, N. W.

doi:10.1115/1.1812321

Cited by 30 publications

(11 citation statements)

References 11 publications

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“…Durham cascade has been used extensively in the past for studying secondary flow loss generation and optimization of enwall geometry for loss reduction, and also as a standard test case for validating turbomachinery CFD methods [29][30][31][32]. At the experimental conditions with a Reynolds number of 4x10 5 , the flow in the blade passage is shown to be transitional subject to a bubble type separation on suction surface [30].…”

Section: Durham Turbine Cascade and Rans Turbulent Flow Solutionsmentioning

confidence: 99%

Implicit Discontinuous Galerkin Solution on Unstructured Mesh for Turbine Blade Secondary Flow

Yao

2019

Journal of Turbomachinery

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To enhance solution accuracy with high-order methods, an implicit solver using the discontinuous Galerkin (DG) discretization on unstructured mesh has been developed. The DG scheme is favored chiefly due to its distinctive feature of achieving a higher-order accuracy by simple internal sub-divisions of a given mesh cell. It can thus relieve the burden of mesh generation for local refinement. The developed method has been assessed in several test cases. First, an examination on the mesh-dependency with different DG orders for discretization has demonstrated the expected mesh convergence order of accuracy correlation. The flow around a cylinder solved with up to the fifth-order accuracy demonstrates the need for a high-order geometrical representation corresponding to the high-order flow field discretization. A calculated turbulent flat plate boundary layer demonstrates the capability of the high-order DG in capturing the laminar sub-layer for a given coarse mesh (y + >20) without a wall function, in a clear contrast to a conventional second-order scheme. The focal test case of the present work is a high-pressure (HP) turbine cascade with the flow losses being strongly influenced by both the laminar separation induced transition on the blade suction surface and the secondary flow development in the endwall region. Fully turbulent RANS solutions consistently overpredict the losses, which can be significantly reduced by an empirically specified transition at a mid-chord point. Of particular interest is a contrasting behavior of pure laminar flow solutions. A steady laminar flow solution is difficult to converge, and even when converging, tends to give an unrealistically large separation. On the other hand when the laminar solution is run in a time-accurate unsteady mode, a qualitatively different flow pattern emerges. The separated shear layer is then shown to lead to coherently shed unsteady vortices with a net entrainment from the main stream to the near-wall region. The resultant time-averaged near-wall flow then effectively becomes a reattached boundary layer. Both overall and distributed losses computed from unsteady laminar solutions are shown to be consistently much better than the fully turbulent RANS solutions. It is remarkable and quite unexpected that for such a seemingly complex 3D flow problem, the straightforward unsteady laminar solutions with no empirical input seem to be comparable with (or slightly better than) the tripped RANS with empirical input.

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Section: Durham Turbine Cascade and Rans Turbulent Flow Solutionsmentioning

confidence: 99%

Implicit Discontinuous Galerkin Solution on Unstructured Mesh for Turbine Blade Secondary Flow

Yao

2019

Journal of Turbomachinery

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“…The vortex was not significantly weakened, but its migration across the passage towards the suction surface was partially blocked. Similar research on end wall profiling was carried out by Gregory-Smith et al [4] , Ingram et al [5,6] . Weiss and Fottner [7] have done experiments on the influence of load distribution on secondary flows in a straight turbine cascade.…”

Section: Introductionmentioning

confidence: 77%

Effect of streamwise fences on secondary flows and losses in a two-dimensional turbine rotor cascade

2006

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To control secondary flows, streamwise fences were attached to end wall of a linear turbine rotor cascade. The cascade had 8 blades of 400 mm long and 175 mm chord. The blades deflected the flow by 120°. The fences were made out of 0.7 mm thick brass sheet and the heights of the fences were 14 mm, 18 mm respectively. The curvature of the fences was the same as that of the blade camber line. The fences were fixed normal to the end wall and at half pitch away from the blades. The experimental program consists of total pressure, static pressure measurements at the inlet and outlet of the cascade, by using five-hole probe. In addition, static pressure on the blade suction surface and pressure surface was also obtained. Fences are effective in preventing the movement of the pressure side leg of the horseshoe vortex. Consequently the accumulation of low energy fluid on the suction surface is minimised. End wall losses are reduced by the fences due to weakening of the end wall cross flow.

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“…However, the lack of correlation between secondary kinetic energy and total loss is reported by Denton and Pullan (2012) . Ingram et al (2005) also demonstrated that a blade designed with a reduced level of secondary kinetic energy can still increase loss. The relation between loss generation rate and Reynolds stresses has been experimentally investigated by MacIsaac et al (2012) .…”

Section: Othersmentioning

confidence: 93%

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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Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling

Cited by 30 publications

References 11 publications

Implicit Discontinuous Galerkin Solution on Unstructured Mesh for Turbine Blade Secondary Flow

Implicit Discontinuous Galerkin Solution on Unstructured Mesh for Turbine Blade Secondary Flow

Effect of streamwise fences on secondary flows and losses in a two-dimensional turbine rotor cascade

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

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