Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls—Part II: Time-Resolved Flow Physics

Schüpbach, Peter; Abhari, Reza S.; Rose, Martin G.; Germain, T.; Raab, I.; Gier, Jochen

doi:10.1115/1.3103926

Cited by 29 publications

(9 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Schuepbach et al [16] confirmed these efficiency improvements by a time-resolved experimental and numerical investigation of the flow physics, which highlighted the presence of reduced blade trailing edge shed vorticity in the contoured wall passage.…”

Section: Introductionmentioning

confidence: 84%

Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

Kadhim

Rona

Gostelow

et al. 2018

International Journal of Mechanical Sciences

View full text Add to dashboard Cite

The interaction of secondary flows with the main passage flow in turbomachines results in entropy generation and in aerodynamic loss. This loss source is most relevant to low aspect ratio blades. One approach for reducing this flow energy loss is by end-wall contouring. However, limited work has been reported on using non-axisymmetric end-walls at the stator casing and on its interaction with the tip leakage flow. In this paper, a non-axisymmetric end-wall design method for the stator casing is implemented through a novel surface definition, towards mitigating secondary flow losses. This design is tested on a three-dimensional axial turbine RANS model built in OpenFOAM Extend 3.2, with − SST turbulence closure. Flow analysis confirm the foundations of the new surface definition approach, which is implemented using Alstom Process and Optimization Workbench (APOW) software. Computer-based optimization of the surface topology is demonstrated towards automating the design process of axial turbines in an industrial design workflow. The design is optimized using the total pressure loss across the first stator and across the full stage, as the target function. Numerical predictions of the 1.5 stage axial turbine show the positive impact of the optimized casing design on the efficiency that increases by 0.69% against the benchmark axisymmetric stage from RTWH Aachen, which is validated against experiment. The new non-axisymmetric casing is also beneficial at off-design condition. The effective mitigation of the secondary flows is predicted to give a 0.73% efficiency gain off-design.

show abstract

Section: Introductionmentioning

confidence: 84%

Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

Kadhim

Rona

Gostelow

et al. 2018

International Journal of Mechanical Sciences

View full text Add to dashboard Cite

show abstract

“…Experimental validation by Hartland et al [11] found a 30% reduction in aerodynamic losses for the contoured wall relative to a flat wall. Endwall contouring in the studies of Germain et al [12] and Schuepbach et al [13] produced an overall stage efficiency improvement of 1.0% 6 0.4% in a 1-1/2 stage turbine, which was largely attributed to reductions in the stator time-averaged and unsteady losses. Praisner et al [14] designed a nonaxisymmetric endwall contour based on secondary loss reduction metrics for the airfoil in this study.…”

Section: Relevant Past Studiesmentioning

confidence: 95%

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

Lynch

Thole

2015

Volume 5B: Heat Transfer

View full text Add to dashboard Cite

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter. Friction coefficients obtained with the oil film interferometry method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

show abstract

“…16 and Schüpbach et al. 17 designed NAEP for a turbine by using an automatic numerical optimization method, which resulted in reduced secondary flow and an improvement of stage efficiency by 1% ± 0.4%. Poehler et al.…”

Section: Introductionmentioning

confidence: 99%

Flow physics of highly loaded tandem compressor cascade with non-axisymmetric endwall profiling

Cao

Guo

Song

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part A:

View full text Add to dashboard Cite

Tandem configuration is an effective methodology to reduce flow separation on compressor blade suction surface and to improve blade loading. However, in modern highly loaded cases, corner separation remains as its single blade counterpart. In this study, non-axisymmetric endwall profiling (NAEP) was utilized in a highly loaded tandem cascade (diffusion factor D = 0.69), aiming at reducing its severe corner separation and revealing the unique flow mechanism while NAEP is utilized in tandem cascade. NAEP was designed in both forward (F) blade and rare (R) blade separately, and was investigated numerically in tandem environment. Results show that, NAEP in F blade passage can effectively eliminate the corner separation and reduce loss generation, whereas NAEP in R blade passage has no positive effect on corner separation and even promotes loss production. The optimal NAEP approximately removes the corner separation completely, with loss coefficient reducing by as much as 37.8%. The optimal NAEP for the tandem cascade features optimal axial location at the origin of corner separation. There is an optimal NAEP height (0.02 of blade height), under which NAEP can achieve pretty good control effect while the peak of NAEP varies in a large axial location range. In the tandem configuration, it is found that NAEP transfers blade loading from R blade to F blade; the static pressure increases significantly for the entire cascade, but the static pressure distribution of F blade does not exhibit as the design intent of NAEP. In addition, it is interesting to find that the flow turning near endwall reduces after endwall profiling, which is unique in tandem cascade and is contrast to the view on conventional configuration. On the contrary, NAEP in R blade has no influence on the corner separation of the tandem cascade; due to the decrement of cross-passage pressure gradient for R blade, the flow overturning near endwall reduces.

show abstract

Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls—Part II: Time-Resolved Flow Physics

Cited by 29 publications

References 21 publications

Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

Optimization of the non-axisymmetric stator casing of a 1.5 stage axial turbine

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

Flow physics of highly loaded tandem compressor cascade with non-axisymmetric endwall profiling

Contact Info

Product

Resources

About