Numerical Study of Effect of Streamwise End Wall Fences on Secondary Flow Losses in Two Dimensional Turbine Rotor Cascade

The interaction of secondary flow with the main passage flow results in entropy generation; this accounts for considerable losses in turbomachines. Low aspect ratio blades in an axial turbine lead to a high degree of secondary flow losses. A particular interest is the reduction in secondary flow strength at the turbine casing, which adversely affects the turbine performance. This paper presents a selective review of effective techniques for improving the performance of axial turbines by turbine end wall modifications. This encompasses the use of axisymmetric and non-axisymmetric end wall contouring and the use of fences. Specific attention is given to non-axisymmetric end walls and to their effect on secondary flow losses. A baseline three-dimensional steady RANS k-ω SST model, with axisymmetric walls, is validated against experimental measurements from the Institute of Jet Propulsion and Turbomachinery at the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Germany, with comparative solutions generated by ANSYS Fluent and OpenFOAM. The predicted performance of the stator passage with an axisymmetric casing is compared with that from using a contoured casing with a groove designed using the Beta distribution function for guiding the groove shape. The prediction of a reduced total pressure loss coefficient with the application of the contoured casing supports the groove design approach based on the natural path of the secondary flow features. This work also provided an automated workflow process, linking surface definition in MATLAB, meshing in ICEM CFD, and flow solving and post-processing OpenFOAM. This has generated a casing contouring design tool with a good portability to industry, to design and optimize new turbine blade passages.

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Numerical study of the influence of splitter geometry on secondary flow control

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650920962247 ◽

2020 ◽

pp. 095765092096224

Author(s):

Tao Bian ◽

Xin Shen ◽

Jun Feng

Keyword(s):

Flow Control ◽

Secondary Flow ◽

Numerical Study ◽

Guide Vane ◽

Axial Fan ◽

Suction Surface ◽

Flow Losses ◽

Spacing Ratio ◽

Specific Configuration ◽

End Wall

In turbmachinery, splitters are used to control secondary flow and to improve the aerodynamic performance of outlet guide vane (OGV) of axial fan. However, there is few information in the open literature focusing on the effect of the splitter geometry on the secondary flow control. In this work, the numerical investigations were performed for NACA 65-010 profile with different splitters. The spacing ratio of the main blade was 1, the spacing between the splitters and the main blade was 30mm. Three different splitters were compared to investigate the effect of the splitter geometry on secondary flow control. The flow structures near the end-wall, the streamlines on the suction surface of blade and the distribution of the flow losses on the trailing edge of blade was shown and discussed. The results showed the splitters can control the secondary flow and reduce the area of the high flow losses at the junction of end-wall and blade. However, the flow separation of the splitters also causes flow losses in the wake behind the splitters. Therefore, only the specific configuration of splitters can reduce the flow losses of the blade.

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End-Wall Secondary Flow Control Using Engineered Residual Surface Structure

Volume 2B: Turbomachinery ◽

10.1115/gt2016-57347 ◽

2016 ◽

Cited By ~ 2

Author(s):

X. Miao ◽

Q. Zhang ◽

C. Atkin ◽

Z. Sun

Keyword(s):

Flow Control ◽

Surface Structure ◽

Secondary Flow ◽

End Milling ◽

Numerical Study ◽

Small Scale ◽

Duct Flow ◽

Design Guideline ◽

Residual Structure ◽

End Wall

Residual surface roughness is often introduced in the manufacture process with ball-end or fillet-end milling. Instead of paying extra cost to remove these small-scale residual surface structures, there is a potential usage of them as flow control device. This numerical study therefore explores the ability of engineered surface structure in controlling the endwall secondary flow in turbomachinery. The CFD method is validated against the existing experimental data obtained for a 90 degree turning duct flow with a single rib fence placed on the end-wall. The working principle of the engineered surface structure is revealed through detailed analysis on the flow produced by multiple small fences and grooves mimicking the residual surface. The results consistently show that addition of engineered residual structure on flow surface can effectively reduce the magnitude of stream-wise vorticity associated with secondary flow and alleviate its lift-off motion. In the end, a general working mechanism and design guideline for optimizing the residual structure are summarized.

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The Influence of Non-Axisymmetric End Wall in a High-Load Compressor Stage With Tandem Stator

Volume 2A: Turbomachinery ◽

10.1115/gt2019-90334 ◽

2019 ◽

Author(s):

Xiangjun Li ◽

Wuli Chu

Keyword(s):

Optimization Design ◽

Numerical Study ◽

Suction Side ◽

High Load ◽

Recirculation Region ◽

Wall Region ◽

Two Dimensional ◽

Corner Separation ◽

Positive Effects ◽

End Wall

Abstract The application of tandem blade in compressors has been study for decades. According to the open literature, using tandem blade can effectively extend the working range of the compressor under high incidence. Many earlier researches focused on the two-dimensional influence of tandem blade, and revealed that a proper arrangement on the positions of the front and the rear blade would allow the boundary layer on the suction side to develop in a more favourable way to control the two-dimensional separation. However, because of the serious corner separation and higher loss in the end wall region of high-load compressors. Some recent researches started to focus on the three-dimensional flow for further understanding the effect of the tandem setup. As an effective way to influence the end wall flow, the profiled end wall can be applied to both turbines and compressors to reduce the end wall loss. However, the co-work of tandem blade and profiled end wall was seldom reported. In this paper, a numerical research was carried out based on a single-stage high-load compressor with a tandem stator. After a numerical study for the hub separation. A series of optimization design were carried out for the hub end wall of the rotor, stator and the stage to improve the overall efficiency. The discussion revealed the positive effects of the optimum profiled end wall on the tandem stator were on one hand to limit the extension of the recirculation region of the front passage and on another hand to suppress the suction side corner separation in the rear passage. The efficiency of the upstream rotor was also reduced in small value because the variation of the through flow. After that, the indirect influence of the rotor profiled end wall on the stator and the stage profiling case were also analysed. The optimum stage hub profiling did not equal to the simple combination of the optimum stator and the rotor hub end wall. It is found that in the stage profiling case, the variation of loss in stator and rotor are very well adjusted and balanced by the optimization algorithm. The improvement of efficiency therefore achieved the highest value.

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Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear LP Turbine Cascade

10.1115/gtindia2021-76008 ◽

2021 ◽

Author(s):

Anand P. Darji ◽

Beena D. Baloni ◽

Chetan S. Mistry

Keyword(s):

Flow Field ◽

Secondary Flow ◽

Turbulence Model ◽

Turbulence Intensity ◽

Numerical Study ◽

Turbine Cascade ◽

Wall Flow ◽

End Wall ◽

Inflow Conditions ◽

Secondary Flow Field

Abstract End wall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modify the blade loading and overall performance in terms of stable operating range. Present study aimed to determine the end wall flow streams in a low speed low pressure linear turbine cascade vane using numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at end wall. Location of generation of horseshoe vortex streams and subsequent vortex patterns are identified in the section. The selection of suitable turbulence model among SST (Shear Stress Transport) k–ω and SST γ–θ to identify end wall flow streams is studied in prior in the section. The steady state numerical study is performed using Reynolds Averaged Navier-Stoke’s Equations closed by SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in later section. The second section includes effect of flow incidence and turbulence intensity on the end wall secondary flow field. Inflow incidences considered for the study are −20°, −10°, 0° (design incidence), +10° and +20°. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an end wall and found the change in behavior with an inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

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Entropy Generation in a 2-D Cascade at Different Angles of Attack: A Numerical Study

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/97-gt-097 ◽

1997 ◽

Cited By ~ 1

Author(s):

Gianni Natalini ◽

Enrico Sciubba

Keyword(s):

Gas Turbine ◽

Entropy Generation ◽

Stokes Equations ◽

Numerical Study ◽

Angle Of Attack ◽

Turbine Rotor ◽

Loss Coefficient ◽

Entropy Generation Rate ◽

Two Dimensional ◽

Design Point

This paper presents the results of an entropy generation calculation made on a representative gas turbine rotor blade; in particular, the numerical study has dealt with the different flowfields which are encountered when the angle of attack is varied in a two-dimensional cascade on axial, internally cooled gas turbine rotor. The analysis takes into consideration a two-dimensional cascade at medium Reynolds number (Rechord = 225000), sub-sonic Mach number (Main = 0.27), and steady state. The full Navier-Stokes equations of motion for a turbulent compressible viscous flow, together with the appropriate energy equation, are solved via a standard finite elements code with a k-ε closure, so that complete velocity- and temperature fields are obtained (including boundary-layer effects, via proper wall functions). These fields are then used to compute the entropy generation rates corresponding to the viscous- (Ṡv) and thermal (Ṡr) dissipation. Several configurations have been numerically tested, the reference one being at design conditions, and the remaining being obtained from it by varying the angle of attack α (defined as the angle, measured ccw, between the relative velocity vector W1 and the tangent to the blade chord at impingement point), to simulate volume flowrate variations. A commercial finite-element code (FIDAP, by FDI Inc.) has been modified to allow for the calculation of the local values of the entropy generation rates, the thermal- and viscous portions of which have been computed separately. The results at design point are shown to agree well with the available cascade performance data. The entropy generations rates are then used to compute the so-called entropy loss coefficient (a better name for which would be that of irreversibility coefficient, ζ, defined as:ζ=T0Δsh1s-h2iwhere T0 is the reference ambient temperature, Δs is the total local entropy generation rate (sum of the viscous- and thermal components), and h1i and h2i are the stagnation enthalpy upstream of the rotor and the ideal exit enthalpy respectively. The results are shown under the form of cp - and ζ graphs computed for different angles of attack α (from −4.4 to +7.6 degrees), and are representative of realistic situations which could arise in actual gas turbine rotors. The loss coefficient ζ is shown to attain a minimum value at design point. Integral values for the entropy generation rates are also computed, and total entropy losses are thus computed for the various configurations. Maps of the viscous- and thermal entropy generation rates are shown for each angle of attack, where of interest.

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Growth of Secondary Flow Losses Downstream of a Turbine Blade Cascade

Volume 1: Aircraft Engine; Turbomachinery ◽

10.1115/85-igt-35 ◽

1985 ◽

Author(s):

L. D. Chen ◽

S. L. Dixon

Keyword(s):

Boundary Layer ◽

Secondary Flow ◽

Total Pressure ◽

Turbine Cascade ◽

Pressure Losses ◽

Flow Losses ◽

Blade Cascade ◽

Flow Loss ◽

Loss Coefficients ◽

End Wall

End wall total pressure losses downstream of a low-speed turbine cascade have been measured at several planes in order to determine the changes in secondary flow loss coefficients and the growth of the mixing loss with distance downstream. The results obtained are compared with various published secondary flow loss correlations in an attempt to explain some of the anomalies which presently exist. The paper includes some new correlations including one for the important gross secondary loss coefficient YSG with loading and aspect ratio parameters as well as the upstream boundary layer parameters.

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Comparison of 2D and 3D Airfoils in Combination With Non Axisymmetric End Wall Contouring: Part 2 — Numerical Investigations

Volume 2B: Turbomachinery ◽

10.1115/gt2016-56914 ◽

2016 ◽

Cited By ~ 1

Author(s):

Oliver Curkovic ◽

Tobias W. Zimmermann ◽

Manfred Wirsum ◽

Andrew Fowler ◽

Kush Patel

Keyword(s):

Secondary Flow ◽

Gas Turbines ◽

Potential Method ◽

Labyrinth Seals ◽

Flow Losses ◽

Positive Effects ◽

Flow Phenomena ◽

2D And 3D ◽

End Wall ◽

The Impact

Secondary flow phenomena have a considerable part in the efficiency loss in turbomachinery. A potential method to reduce these secondary flow losses is tangential end wall contouring inside the blade passages. The present paper is the second of two papers which investigate the impact of tangential end wall contouring on 2D and 3D airfoils compared to a baseline configuration. The first paper summarizes the experimental investigation on a 2-stage air driven turbine test rig located at the Institute of Power Plant Technology, Steam and Gas Turbines RWTH Aachen University. To enhance the impact of the tangential end wall contours (TEWC) on the near wall flow, the rotor cavities are sealed by means of combined brush- and labyrinth seals. The stator cavities are sealed by labyrinth seals, only. This paper investigates the flow phenomena using CFD with the commercial software package ANSYS 15.0©. The brush seals are modeled by using the porous body approach and are calibrated using pressure drop measurements across the first rotor cavity. The experimental data will be presented and is used to validate the numerical model. For this, circumferential plots for the measurement planes are shown. In addition a detailed description of the changes in vortex formations as well as blade loading will be given for the various configurations. Finally a discussion of the impact on the turbine’s efficiency is given. It has been found, that for steady CFD simulations the use of stage interfaces suppresses the positive effects of the tangential end wall contour onto the downstream blade row.

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