Anisotropic Eddy Viscosity in the Secondary Flow of a Low-Speed Linear Turbine Cascade

2011 ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander
Keyword(s):  
Turbulent Flow ◽  
Secondary Flow ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Leading Edge ◽  
Boussinesq Approximation ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Low Speed ◽  
Sst Turbulence Model

The final losses within a turbulent flow are realized when eddies completely dissipate to internal energy through viscous interactions. The accurate prediction of the turbulence dissipation, and therefore the losses, requires turbulence models which represent, as accurately as possible, the true flow physics. Eddy viscosity turbulence models, commonly used for design level computations, are based on the Boussinesq approximation and inherently assume the eddy viscosity field is isotropic. The current paper compares the computational predictions of the flow downstream of a low-speed linear turbine cascade to the experimentally measured results. Steady-state computational simulations were performed using ANSYS CFX v12.0 and employed the shear stress transport (SST) turbulence model with the γ-Reθ transition model. The experimental data includes measurements of the mean and turbulent flow quantities. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Data is presented for two axial locations: 120% and 140% of the axial chord (Cx) downstream of the leading edge. The computed loss distribution and total bladerow losses are compared to the experimental measurements. Differences are noted and a discussion of the flow structures provides insights into the origin of the differences. Contours of the shear eddy viscosity are presented for each axial plane. The secondary flow appears highly anisotropic, demonstrating a fundamental difference between the computed and measured results. This raises questions as to the validity of using two-equation turbulence models, which are based on the Boussinesq approximation, for secondary flow predictions.

Effects of an Upstream Cavity on the Secondary Flow in a Transonic Turbine Cascade

2010 ◽  
Author(s):  
H. M. Abo El Ella ◽  
S. A. Sjolander ◽  
T. J. Praisner
Keyword(s):  
Mach Number ◽  
Secondary Flow ◽  
Ultra Violet ◽  
Leading Edge ◽  
Reactive Dye ◽  
Surface Flow ◽  
Flow Structures ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Blow Down

This paper examines experimentally the effects of an upstream cavity on the flow structures and secondary losses in a transonic linear turbine cascade. The cavity approximates the endwall geometry resulting from the platform overlap at the interface between stationary and rotating turbine blade rows. Previous investigations of the effects of upstream cavity geometries have been conducted mainly at low-speed conditions. The present work aims to extend such research into the transonic regime with a more engine representative upstream platform geometry. The investigations were carried out in a blow-down type wind tunnel. The cavity is located at 30% of axial-chord from the leading edge, extends 17% of axial-chord in depth, and is followed by a smooth ramp to return the endwall to its nominal height. Two cascades are examined for the same blade geometry: the baseline cascade with a flat endwall and the cascade with the cavity endwall. Measurements were made at the design incidence and the outlet design Mach number of 0.80. At this condition, the Reynolds number based on outlet velocity is about 600,000. Off-design outlet Mach numbers of 0.69, and 0.89 were also investigated. Flowfield measurements were carried out at 40% axial-chord downstream of the trailing edge, using a seven-hole pressure probe, to quantify losses and identify the flow structures. Additionally, surface flow visualization using an ultra-violet reactive dye was employed at the design Mach number, on the endwall and blade surfaces, to help in the interpretation of the flow physics. The experimental results also include blade-loading distributions, and the probe measurements were processed to obtain total-pressure loss coefficients, and stream-wise vorticity distributions. It was found that the presence of the upstream cavity noticeably altered the structure and the strength of the secondary flow. Some effect on the secondary losses was also evident, with the cavity having a larger effect at the higher Mach number.

Measurements of Losses and Reynolds Stresses in the Secondary Flow Downstream of a Low-Speed Linear Turbine Cascade

2010 ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander ◽  
T. J. Praisner
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Hole Pressure ◽  
The Mean

Experimental measurements of the mean and turbulent flow field were preformed downstream of a low-speed linear turbine cascade. The influence of turbulence on the production of secondary losses is examined. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Each probe was traversed downstream of the cascade along planes positioned at three axial locations: 100%, 120% and 140% of the axial chord (Cx) downstream of the leading edge. The seven-hole pressure probe was used to determine the local total and static pressure as well as the three mean velocity components. The rotatable x-type hotwire probe, in addition to the mean velocity components, provided the local Reynolds stresses and the turbulent kinetic energy. The axial development of the secondary losses is examined in relation to the rate at which mean kinetic energy is transferred to turbulent kinetic energy. In general, losses are generated as a result of the mean flow dissipating kinetic energy through the action of viscosity. The production of turbulence can be considered a preliminary step in this process. The measured total pressure contours from the three axial locations (1.00, 1.20 and 1.40Cx) demonstrate the development of the secondary losses. The peak loss core in each plane consists mainly of low momentum fluid that originates from the inlet endwall boundary layer. There are, however, additional losses generated as the flow mixes with downstream distance. These losses have been found to relate to the turbulent Reynolds stresses. An examination of the turbulent deformation work term demonstrates a mechanism of loss generation in the secondary flow region. The importance of the Reynolds shear stress to this process is explored in detail.

Effects of an Upstream Cavity on the Secondary Flow in a Transonic Turbine Cascade

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
H. M. Abo El Ella ◽  
S. A. Sjolander ◽  
T. J. Praisner
Keyword(s):  
Mach Number ◽  
Secondary Flow ◽  
Ultra Violet ◽  
Leading Edge ◽  
Surface Flow ◽  
Flow Structures ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Streamwise Vorticity ◽  
Blow Down

This paper examines experimentally the effects of an upstream cavity on the flow structures and secondary losses in a transonic linear turbine cascade. The cavity approximates the endwall geometry resulting from the platform overlap at the interface between stationary and rotating turbine blade rows. Previous investigations of the effects of upstream cavity geometries have been conducted mainly at low-speed conditions. The present work aims to extend such research into the transonic regime with a more engine representative upstream platform geometry. The investigations were carried out in a blow-down type wind tunnel. The cavity is located at 30 % of axial chord from the leading edge, extends 17 % of axial-chord in depth, and is followed by a smooth ramp to return the endwall to its nominal height. Two cascades are examined for the same blade geometry: the baseline cascade with a flat endwall and the cascade with the cavity endwall. Measurements were made at the design incidence and the outlet design Mach number of 0.80. At this condition, the Reynolds number based on outlet velocity is about 600,000. Off-design outlet Mach numbers of 0.69, and 0.89 were also investigated. Flowfield measurements were carried out at 40 % axial-chord downstream of the trailing edge, using a seven-hole pressure probe, to quantify losses and identify the flow structures. Additionally, surface flow visualization using an ultra-violet reactive dye was employed at the design Mach number, on the endwall and blade surfaces, to help in the interpretation of the flow physics. The experimental results also include blade-loading distributions, and the probe measurements were processed to obtain total-pressure loss coefficients, and streamwise vorticity distributions. It was found that the presence of the upstream cavity noticeably altered the structure and the strength of the secondary flow. Some effect on the secondary losses was also evident, with the cavity having a larger effect at the higher Mach number.

Measurements of Losses and Reynolds Stresses in the Secondary Flow Downstream of a Low-Speed Linear Turbine Cascade

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander ◽  
T. J. Praisner
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Hole Pressure ◽  
The Mean

Experimental measurements of the mean and turbulent flow field were preformed downstream of a low-speed linear turbine cascade. The influence of turbulence on the production of secondary losses is examined. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Each probe was traversed downstream of the cascade along planes positioned at three axial locations: 100%, 120%, and 140% of the axial chord (Cx) downstream of the leading edge. The seven-hole pressure probe was used to determine the local total and static pressure as well as the three mean velocity components. The rotatable x-type hotwire probe, in addition to the mean velocity components, provided the local Reynolds stresses and the turbulent kinetic energy. The axial development of the secondary losses is examined in relation to the rate at which mean kinetic energy is transferred to turbulent kinetic energy. In general, losses are generated as a result of the mean flow dissipating kinetic energy through the action of viscosity. The production of turbulence can be considered a preliminary step in this process. The measured total pressure contours from the three axial locations (1.00, 1.20, and 1.40Cx) demonstrate the development of the secondary losses. The peak loss core in each plane consists mainly of low momentum fluid that originates from the inlet endwall boundary layer. There are, however, additional losses generated as the flow mixes with downstream distance. These losses have been found to relate to the turbulent Reynolds stresses. An examination of the turbulent deformation work term demonstrates a mechanism of loss generation in the secondary flow region. The importance of the Reynolds shear stresses to this process is explored in detail.

scholarly journals Incidence Angle and Pitch-Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1992 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 degrees, and for three pitch-chord ratios: s/c = 0.58,0.73,0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five hole probe in a plane located at 50% of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots show in detail how much the secondary flow field is modified both by incidence and cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch averaged loss and of the deviation angle, when incidence or pitch-chord ratio is varied.

Aerodynamics of Cooling Jets Introduced in the Secondary Flow of a Low-Speed Turbine Cascade

1990 ◽  
Vol 112 (3) ◽  
pp. 539-546 ◽  
Author(s):  
F. Bario ◽  
F. Leboeuf ◽  
A. Onvani ◽  
A. Seddini
Keyword(s):  
Secondary Flow ◽  
Side Wall ◽  
Velocity Fields ◽  
Measuring Apparatus ◽  
Flow Ratio ◽  
Turbine Cascade ◽  
Hot Wire ◽  
Local Pressure ◽  
Low Speed ◽  
Jet Behavior

The aerodynamic behavior of cold discrete jets in a cold secondary flow is investigated. Configurations including single jets and rows of jets are studied. These jets are introduced through the side wall of a low-speed nozzle turbine cascade. The experimental setup and the jet behavior are fully described. The effects of location with respect to the blades, mass flow ratio, yaw, and incidence angles on the aerodynamics of single jets are investigated. The influence of neighboring jets is detailed in the case of multiple jet configurations. The interaction with the secondary flow is presented. The local pressure and velocity fields, trajectories, and visualizations are discussed. The measuring apparatus includes a five-hole probe and a hot wire for intermittency measurements.

Numerical Investigation on a High Endwall Angle Turbine With Swept-Curved Vanes

2018 ◽  
Author(s):  
Fusheng Meng ◽  
Jie Gao ◽  
Weiliang Fu ◽  
Xuezheng Liu ◽  
Qun Zheng
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Heat Load ◽  
Leading Edge ◽  
Field Calculation ◽  
Prediction Ability ◽  
Expansion Turbine ◽  
Sst Turbulence Model ◽  
Flow Loss ◽  
Lp Turbine

In a high endwall angle turbine, large meridional expansion can cause the strong secondary flow at the endwall, which results in a larger endwall flow loss than the small meridional expansion turbine. The endwall heat transfer is strongly affected by secondary flow effect. In order to optimize the endwall flow to reduce the flow loss and optimize the distribution of heat load, the swept-curved method was used in this study. The swept-curved method was investigated on a transonic second stator (S2) with large meridional expansion in a Low-Pressure (LP) Turbine. Validation studies were performed to investigate the aerodynamic and the heat transfer prediction ability of shear stress transport (SST) turbulence model. The influence of different shapes of the stacking line, including forward-swept, backward-swept, positive-curved and negative-curved, were investigated through numerical simulation. The parameterized control of swept-curved height and angle were adopted to optimize the performance of the aerodynamic and heat transfer. 3D flow field calculation captured the relatively accurate flow structures in the parts of endwall and near endwall. Heat transfer behaviors were explored by means of isothermal wall temperature and Nusselt number (Nu) distribution. The results show that the maximal heat transfer coefficient at the leading edge, for the formation of horseshoe vortexes that cause the high velocity towards the endwall. The swept vane can improve the static pressure and heat load distribution at the endwall region, which decreases the area-averaged shroud heat flux by 2.6 percent and the loss coefficient 1.3 percent.

Comparative Studies of Turbulence Models Application in Thermal Hydraulic Analysis of Nuclear Reactor Core

2010 ◽  
Author(s):  
Heyi Zeng ◽  
Yun Guo
Keyword(s):  
Fluid Dynamics ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Nuclear Reactor ◽  
Nuclear Reactors ◽  
Reactor Core ◽  
Turbulence Models ◽  
Flow Phenomena ◽  
Nuclear Reactor Core ◽  
Complicated Geometry

Rod bundles are essential elements of pressurized water nuclear reactors. They consist of tightly packed arrays of rods, which contain the nuclear fuel and are surrounded by flowing liquid coolant. Flow phenomena in the subchannels bounded by adjacent rods are quite complex and exhibit patterns not present in pipe flows. Development of nuclear reactors and of fuel assemblies requires fluid dynamics analysis activities. The detailed prediction of velocity and temperature distributions inside a rod bundle is one of the main objectives of the current research in reactor thermal hydraulics. Computational fluid dynamics (CFD) simulation is of great interest for the design and safety analysis of nuclear reactors since it has recently achieved considerable advancements. In the present studies, numerical simulation were performed on developed turbulent flow through core subchannels with configurations of triangle and square lattice, and impact of different turbulence models built-in software package FLUENT upon simulation results of velocity distribution and hydraulic characteristics in channels with complicated geometry were compared and analyzed. Results show that simulation result greatly depends on turbulence models. Due to the complicated geometric construction, the complicated three-dimensional turbulent flow shows highly anisotropic characteristics. Turbulence models assuming isotropic turbulent viscosity failed to predict secondary flow phenomena during turbulent flow in fuel assembly channel. By solving Reynolds stresses transport equations, more elaborate Reynolds stress model (RSM) can catch secondary flow accurately. The present studies have provided valuable references and guidelines for further investigation on convective heat transfer simulation in complicated geometry and thermalhydrulic analysis of nuclear reactor core.

Computational Study of a Transonic Turbine Cascade: Validation and Comparison of Griding Approaches and Challenges

2014 ◽  
Author(s):  
H. M. Abo El Ella ◽  
M. Kibsey ◽  
S. A. Sjolander
Keyword(s):  
Computational Study ◽  
Leading Edge ◽  
Pressure Probe ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Streamwise Vorticity ◽  
Blow Down ◽  
Flow Physics ◽  
Transonic Turbine ◽  
Unstructured Meshing

This paper presents a computational study, with some experimental validation, of a low-turning transonic turbine cascade. A comparison is presented between the time-consuming and difficult to generate hexa-structured meshing approach, and the mostly automated tetra-unstructured meshing approach. The paper compares the predicted flow physics and losses, with discussion of the challenges in griding and convergence between both approaches. Computations were carried out using a commercial RANS solver (ANSYS CFX 12) using the Shear Stress Transport turbulence model, and the Gamma-Theta transition model. The computational domain encompassed a half blade span, and one blade pitch with periodic boundary conditions; griding for both approaches was done using ANSYS ICEM CFD. Computational results from both griding approaches were compared to corresponding experimental data. The outlet Mach number was 0.90. The experiment was carried out using a linear cascade in a blow-down type wind tunnel. Downstream seven-hole pressure probe measurements at 1.8 axial chord lengths from the leading edge provided loss, streamwise vorticity, and secondary kinetic energy distributions and integrated coefficient values. It was found that both griding approaches predicted similar downstream endwall flow structures to those observed in the experiment. The tetra-unstructured mesh solution predicted higher losses, but both predicted lower losses than the experiment. Overall results suggest that for capturing of the basic flow physics, both approaches suffice, with the tetra-unstructured being the much easier approach, but with limitations on the level of grid refinement. For more accurate capturing of the flow physics, the time-consuming and difficult to generate hexa-structured meshing approach can be justified.

Incidence Angle and Pitch–Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1993 ◽  
Vol 115 (3) ◽  
pp. 383-391 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 deg, and for three pitch-chord ratios: s/c = 0.58, 0.73, 0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five-hole probe in a plane located at 50 percent of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots, show in detail how much the secondary flow field is modified both by incidence and by cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch-averaged loss and of the deviation angle, when incidence or pitch–chord ratio is varied.

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