Numerical Study of the Flow Past an Axial Turbine Stator Casing and Perspectives for its Management

2017 ◽  
Author(s):  
Hakim T. K. Kadhim ◽  
Aldo Rona ◽  
Hayder M. B. Obaida ◽  
J. Paul Gostelow
Keyword(s):  
Secondary Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Design Tool ◽  
Flow Strength ◽  
Ansys Fluent ◽  
Axial Turbine ◽  
Pressure Loss Coefficient ◽  
Flow Losses ◽  
End Wall

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.

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

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.

A Numerical Study of Secondary Flows in a 1.5 Stage Axial Turbine Guiding the Design of a Non-Axisymmetric Hub

2017 ◽  
Author(s):  
Hayder M. B. Obaida ◽  
Hakim T. K. Kadhim ◽  
Aldo Rona ◽  
Katrin Leschke ◽  
J. Paul Gostelow
Keyword(s):  
Secondary Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Suction Side ◽  
Side Branch ◽  
Secondary Flows ◽  
Design Work ◽  
Axial Turbine ◽  
Turbine Performance

The performance of axial flow turbines is affected by losses from secondary flows that result in entropy generation. Reducing these secondary flow losses improves the turbine performance. This paper investigates the effect of applying a non-axisymmetric contour to the hub of a representative one-and-half stage axial turbine on the turbine performance. An analytical end-wall hub surface definition with a guide groove is used to direct the pressure side branch of the horseshoe vortex away from the blade suction side, so to retard its interaction with the suction side secondary flow and thus decrease the losses. This groove design is a development of the concept outlined in Obaida et al. (2016). A baseline three-dimensional steady RANS k-ω SST model, with axisymmetric walls, is validated against reference experimental measurements from a one-and-half stage turbine at the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen, Germany. The CFD predictions of the non-axisymmetric hub with the guide groove show a decrease in the total pressure loss coefficient. The design work-flow is generated using the Alstom Process and Optimisation Workbench (APOW), which sensibly reduced the designer workload. The implementation of the guide groove has excellent portability to the turbomachinery industry and this makes this method promising for delivering the UK energy agenda through more efficient power turbines.

End-Wall Film Cooling Through Fan-Shaped Holes With Different Area Ratios

2006 ◽  
Vol 129 (2) ◽  
pp. 212-220 ◽  
Author(s):  
Giovanna Barigozzi ◽  
Giuseppe Franchini ◽  
Antonio Perdichizzi
Keyword(s):  
Secondary Flow ◽  
Mass Flow ◽  
Film Cooling ◽  
Three Dimensional ◽  
Wide Band ◽  
Lateral Spreading ◽  
Area Ratio ◽  
Adiabatic Effectiveness ◽  
Flow Effects ◽  
End Wall

The present paper reports on the aerothermal performance of a nozzle vane cascade, with film-cooled end walls. The coolant is injected through four rows of cylindrical holes with conical expanded exits. Two end-wall geometries with different area ratios have been compared. Tests have been carried out at low speed (M=0.2), with coolant to mainstream mass flow ratio varied in the range 0.5–2.5%. Secondary flow assessment has been performed through three-dimensional (3D) aerodynamic measurements, by means of a miniaturized five-hole probe. Adiabatic effectiveness distributions have been determined by using the wide-band thermochromic liquid crystals technique. For both configurations and for all the blowing conditions, the coolant share among the four rows has been determined. The aerothermal performances of the cooled vane have been analyzed on the basis of secondary flow effects and laterally averaged effectiveness distributions; this analysis was carried out for different coolant mass flow ratios. It was found that the smaller area ratio provides better results in terms of 3D losses and secondary flow effects; the reason is that the higher momentum of the coolant flow is going to better reduce the secondary flow development. The increase of the fan-shaped hole area ratio gives rise to a better coolant lateral spreading, but appreciable improvements of the adiabatic effectiveness were detected only in some regions and for large injection rates.

Three-Dimensional Pressure Controlled Vortex Design of a Turbine Stage

2012 ◽  
Author(s):  
Qingfeng Deng ◽  
Qun Zheng ◽  
Guoqiang Yue ◽  
Hai Zhang ◽  
Mingcong Luo
Keyword(s):  
Pressure Gradient ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Pressure Control ◽  
Turbine Stage ◽  
Stream Surface ◽  
Control Approach ◽  
Flow Losses ◽  
Pressure Controlled ◽  
Surface Thickness

A three-dimensional (3D) Pressure Controlled Vortex Design (PCVD) method for turbine stage design is proposed and discussed in this paper. The concept is developed from conventional Controlled Vortex Design (CVD) via pressure control approach and CVD technology. By specifying the static pressure and axial velocity distributions, the spanwise pressure gradient incorporated with pressure gradient in streamwise and azimuthal directions is moderated. Not only can profile loss profit from pressure control approach, but also secondary flow can be managed. The reasons for CVD are derived from stream surface thickness and stream surface twist. Through modifying stream surface thickness and inducing large stream surface twist, the secondary flow migrations are controlled properly and orderly. The relations of pressure control approach and CVD technology complement one another and finally lead to a well-posed flow pattern in turbine stage. The first stage redesign of a well-designed low pressure turbine demonstrates this technique application. A significant reduction of secondary flow losses and a corresponding increase of stage efficiency have achieved.

Numerical Study of the Winter-Kennedy Method—A Sensitivity Analysis

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Binaya Baidar ◽  
Jonathan Nicolle ◽  
Chirag Trivedi ◽  
Michel J. Cervantes
Keyword(s):  
Boundary Conditions ◽  
Secondary Flow ◽  
Numerical Study ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Local Flow ◽  
Spiral Case ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Changes

The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ=30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

Experimental and Numerical Investigation Into the Unsteady Interaction of Labyrinth Seal Leakage Flow and Main Flow in a 1.5-Stage Axial Turbine

2004 ◽  
Author(s):  
A. Giboni ◽  
K. Wolter ◽  
J. R. Menter ◽  
H. Pfost
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Navier Stokes ◽  
Experimental Program ◽  
Leakage Flow ◽  
Axial Turbine ◽  
Flow Phenomena ◽  
Grid Points

This paper presents the results of experimental and numerical investigations into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the time dependent interaction between the leakage flow and the main flow. The experimental program consists of time accurate measurements of the three-dimensional properties of the main flow. The region of the entering leakage flow downstream of the rotor trailing edge was of special interest. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at the design operating point of the turbine. The measurement planes behind the three blade rows extend over one pitch from the shroud to the casing. The complex three-dimensional flow field is mapped in great detail by 1,008 points per measurement plane. The time-accurate experimental data of the three measurement planes was compared with the results of unsteady, numerical simulations of the turbine flow. The 3D-Navier-Stokes Solver CFX-TASCflow was used. The experimental and numerical results correspond well and allow detailed analysis of the mixing process. As demonstrated in this paper, the leakage flow causes strong fluctuations of the secondary flow behind the rotor and the second stator. Above all, the high number of numerical grid points reveals both the secondary flow phenomena and the vortex structures of the mixing zone. The time-dependence of both position and intensity of the vortices is shown. The development of the important leakage vortex is illustrated and explained. The paper shows that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimization process of turbomachinery.

scholarly journals Secondary Flow Effects and Mixing of the Wake Behind a Turbine Stator

1982 ◽  
Author(s):  
A. Binder ◽  
R. Romey
Keyword(s):  
Secondary Flow ◽  
Flow Direction ◽  
Three Dimensional ◽  
Detailed Knowledge ◽  
Pressure Loss Coefficient ◽  
Turbine Stator ◽  
Dimensional Measurements ◽  
Order Of Magnitude ◽  
Flow Effects ◽  
Secondary Vortices

In highly loaded turbines with large hub/tip ratios there is a marked increase in secondary flow effects. The optimization of the turbine flow requires detailed knowledge both of three-dimensional cascade flow and of the wake impinging on the downstream rows of airfoils. Therefore, in the DFVLR, thorough investigations of a single-stage turbine with cold air flow were performed. The stator of this turbine was designed for transonic flow and has a hub/tip ratio of 0.756 and an aspect ratio of 0.56. First, measurements were taken without the rotor in several sections behind the turbine stator with special regard to the mixing of the wakes and secondary vortices. Distributions of total pressure loss coefficient and flow direction give the order of magnitude of the mixing losses. Also, position, intensity, structure, and development of secondary vortices are shown. Some complementary measurements were carried out using five-hole probes. They confirm the above described results from two-dimensional measurements.

Interaction of Labyrinth Seal Leakage Flow and Main Flow in an Axial Turbine

2003 ◽  
Author(s):  
A. Giboni ◽  
J. R. Menter ◽  
P. Peters ◽  
K. Wolter ◽  
H. Pfost ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Experimental Program ◽  
Leakage Flow ◽  
Axial Turbine ◽  
Measurement Plane ◽  
Flow Phenomena ◽  
Operating Points

This paper presents the results of an experimental investigation into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the interaction between the leakage flow and the main flow. The experimental program consists of measurements of the three-dimensional properties of the main flow downstream of the rotor trailing edge after the re-injection of the leakage flow. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at different operating points of the turbine. The measurement plane behind the rotor extends over one pitch from the shroud to the casing, with the complex three-dimensional flow field being mapped in great detail by 1,008 measurement points. As demonstrated in this paper, the entering leakage flow not only introduces mixing losses but also predominates the secondary flow behind the rotor and the second stator. The experimental data show that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimisation process of turbomachinery. The high number of measurement points allows detailed analysis of the secondary flow phenomena and of the vortex structures. The time-dependence of the position and the intensity of the vortices is shown and the influence of the turbine’s operating point is presented.

End-Wall Secondary Flow Control Using Engineered Residual Surface Structure

2016 ◽  
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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