Effect of Wakes and Secondary Flow on Re-attachment of Turbine Exit Annular Diffuser Flow

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
David Kluß ◽  
Horst Stoff ◽  
Alexander Wiedermann
Keyword(s):  
New York ◽  
Secondary Flow ◽  
Internal Flow ◽  
Free Jet ◽  
Diffuser Flow ◽  
Ansys Cfx ◽  
Flow Phenomena ◽  
Annular Diffuser ◽  
Commercial Solver ◽  
Turbine Exhaust

In this paper numerical results of wake and secondary flow interaction in diffuser flow fields are discussed. The wake and secondary flow are generated by a rotating wheel equipped with 30 cylindrical spokes with a diameter of 10 mm as a first approach to the turbine exit flow environment. The apex angle of the diffuser is chosen such that the flow is strongly separated according to the well-known performance charts of Sovran and Klomp (1967, “Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross-Section,” in Fluid Mechanics of Internal Flow, Elsevier, New York, pp. 272–319). This configuration has been tested in an experimental test rig at the Leibniz University Hannover (Sieker and Seume 2007, “Influence of Rotating Wakes on Separation in Turbine Exhaust Diffusers,” Paper No. ISAIF8-54). According to these experiments, the flow in the diffuser separates as free jet for low rotational speeds of the spoke-wheel, as expected by theory. However, if the 30 spokes of the upstream wheel rotate beyond the value of 500 rpm the measurements indicate that the flow remains attached to the outer diffuser wall. It will be shown by the present numerical analysis with the commercial solver ANSYS CFX-10.0 that only an unsteady approach using the elaborate scale adaptive simulation with the shear stress transport turbulence model is capable of predicting the stabilizing effect of the rotating wheel to the diffuser flow at larger rotational speeds. The favorable comparison with the experimental data suggests that the mixing effect of wakes and secondary flow pattern is responsible for the reattachment. As a result of our studies, it can be stated that the considerably higher numerical costs associated with unsteady calculations must be accepted in order to increase the understanding of the physical flow phenomena in turbine exit flow and its interaction with the downstream diffuser.

Effect of Wakes and Secondary Flow on Re-Attachment of Turbine Exit Annular Diffuser Flow

2008 ◽  
Author(s):  
David Kluß ◽  
Alexander Wiedermann ◽  
Horst Stoff
Keyword(s):  
Secondary Flow ◽  
Apex Angle ◽  
Test Rig ◽  
Free Jet ◽  
Diffuser Flow ◽  
Ansys Cfx ◽  
Flow Phenomena ◽  
Annular Diffuser ◽  
Sst Turbulence Model ◽  
Commercial Solver

In this paper numerical results of wake and secondary flow interaction in diffuser flow fields are discussed. The wake and secondary flow are generated by a rotating wheel equipped with 30 cylindrical spokes with a diameter of 10 mm as a first approach to the turbine exit flow environment. The apex angle of the diffuser is chosen such that the flow is strongly separated according to the well-known performance charts of Sovran and Klomp [1]. This configuration has been tested in an experimental test rig at the Leibniz University Hannover [2]. According to these experiments, the flow in the diffuser separates as free jet for low rotational speeds of the spoke-wheel as expected by theory. However, if the 30 spokes of the upstream wheel rotate beyond the value of 500 rpm the measurements indicate that the flow remains attached to the outer diffuser wall. It will be shown by the present numerical analysis with the commercial solver ANSYS CFX-10.0 that only an unsteady approach using the elaborate SAS-SST turbulence model is capable of predicting the stabilizing effect of the rotating wheel to the diffuser flow at larger rotational speeds. The favourable comparison with the experimental data suggests that the mixing effect of wakes and secondary flow pattern is responsible for the reattachment. As a result of our studies it can be stated that the considerably higher numerical costs associated with unsteady calculations must be accepted in order to increase the understanding of the physical flow phenomena in turbine exit flow and its interaction with the downstream diffuser.

New Methods for Secondary Flow Phenomena Visualization and Analysis

2019 ◽  
Author(s):  
Mattia Straccia ◽  
Rodolfo Hofmann ◽  
Volker Gümmer
Keyword(s):  
Secondary Flow ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Secondary Flows ◽  
Tip Leakage ◽  
Ansys Cfx ◽  
Flow Phenomena ◽  
Visualization Techniques ◽  
Operating Points

Abstract This work focuses on presenting new techniques for the visualization of Secondary Flow Phenomena (SFP) in transonic turbomachinery. Here, Rotor 37 has been used to develop and apply these techniques in order to study vortices, shocks and secondary flows. They are also used to provide a comparison between turbulence models in Ansys CFX environment, here the Spalart-Allmaras (SA) and Shear Stress Tensor (SST) turbulence models. The scope of this paper is to give an improved understanding of SFP and how their onset and evolution are influenced from the turbulence model. The analysis is based on results of three-dimensional steady-state RANS simulations, for operating points between design point and near-stall condition, achieved by varying the outlet static pressure radial equilibrium distribution at the rotor exit. The new visualization techniques highlight important flow field features less investigated in previous research works, in particular secondary weak strength vortices. They will give a better visualization of and insight to the interaction of the passage shock and the tip leakage vortex, the interaction between vortices and boundary layers and the interaction of the shock wave and endwall boundary layers.

Unsteady Flow Phenomena in Rotating Centrifugal Impeller Passages

1970 ◽  
Vol 92 (1) ◽  
pp. 65-71 ◽  
Author(s):  
E. Lennemann ◽  
J. H. G. Howard
Keyword(s):  
Unsteady Flow ◽  
Secondary Flow ◽  
Centrifugal Impeller ◽  
Bubble Flow ◽  
Hydrogen Bubble ◽  
Visualization Technique ◽  
Rotating Systems ◽  
Flow Phenomena ◽  
Relative Flow ◽  
Zero Flow

The phenomena of unsteady relative flow observed in a centrifugal impeller passage running at part capacity and zero flow are discussed. The mechanisms of passage stall for a shrouded and unshrouded impeller are investigated and a qualitative correlation is developed for the influence of secondary flow and inducer flow on the passage stall. The hydrogen bubble flow visualization technique is extended to higher velocities and rotating systems and provides the method for obtaining the experimental results.

scholarly journals Aerothermal Investigations of Mixing Flow Phenomena in Case of Radially Inclined Ejection Holes at the Leading Edge

1999 ◽  
Author(s):  
Dieter E. Bohn ◽  
Karsten A. Kusterer
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Side ◽  
Blade Surface ◽  
Cooling Fluid ◽  
Flow Phenomena ◽  
Vortex Systems

A leading edge cooling configuration is investigated numerically by application of a 3-D conjugate fluid flow and heat transfer solver, CHT-Flow. The code has been developed at the Institute of Steam and Gas Turbines, Aachen University of Technology. It works on the basis of an implicit finite volume method combined with a multi-block technique. The cooling configuration is an axial turbine blade cascade with leading edge ejection through two rows of cooling holes. The rows are located in the vicinity of the stagnation line, one row is on the suction side, the other row is on the pressure side. The cooling holes have a radial ejection angle of 45°. This configuration has been investigated experimentally by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The numerical domain includes the internal cooling fluid supply, the radially inclined holes and the complete external flow field of the turbine vane in a high resolution grid. Periodic boundary conditions have been used in the radial direction. Thus, end wall effects have been excluded. The numerical investigations focus on the aerothermal mixing process in the cooling jets and the impact on the temperature distribution on the blade surface. The radial ejection angles lead to a fully three dimensional and asymmetric jet flow field. Within a secondary flow analysis it can be shown that complex vortex systems are formed in the ejection holes and in the cooling fluid jets. The secondary flow fields include asymmetric kidney vortex systems with one dominating vortex on the back side of the jets. The numerical and experimental data show a good agreement concerning the vortex development. The phenomena on the suction side and the pressure side are principally the same. It can be found that the jets are barely touching the blade surface as the dominating vortex transports hot gas under the jets. Thus, the cooling efficiency is reduced.

Visualization of Internal Flow Field of Propeller Fan

2017 ◽  
Author(s):  
Takaya Onishi ◽  
H. Sato ◽  
M. Hayakawa ◽  
Y. Kawata
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Laser Light ◽  
Internal Flow ◽  
Light Sheet ◽  
Tip Vortex ◽  
Laser Light Sheet ◽  
Blade Surface ◽  
Similar Tendency ◽  
Flow Phenomena

Propeller fans are required not only to have high performance but also to be extremely quiet. The internal flow field of ventilation propeller fans is even more complicated because they usually have a very peculiar configuration with protruding blades upstream. Thus, many kinds of internal vortices yield which cause noise and their cause and countermeasures are needed to be clarified. The purposes of this paper are to visualize the internal flow of the propeller fan from the static and rotating frame of reference. The internal flow visualization measured from the static frame gives approximately the scale of the tip vortex. The visualization from the rotating coordinate system yields a better understanding of the flow phenomena occurring at the specific blade. The experiment is implemented by using a small camera mounted on the shaft of the fan and rotated it to capture the behavior of the vortices using a laser light sheet to irradiate the blade surface. Hence, the flow field of the specific blade could be understood to some extent. The visualized results are compared with the CFD results and these results show a similar tendency about the generation point and developing process of the tip vortex. In addition, it is found that the noise measurement result is relevant to the effect of tip vortex from the visualization result.

Vorticity Growth Formed in Vicinity of a Wall on a Moving Elastic Airfoil

2021 ◽  
Author(s):  
Masaki Fuchiwaki
Keyword(s):  
Growth Process ◽  
Fluid Structure Interaction ◽  
Single Layer ◽  
Spatial Gradient ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Ansys Cfx ◽  
Macro Scale ◽  
Dynamic Forces ◽  
Flow Phenomena

Abstract The flow field around moving airfoils capable of flexible elastic deformation has become a focus of attention. These flow fields may be understood as a fluid-structure interaction (FSI) problem, and the motion and deformation of elastic airfoils, as well as the associated vortex flow phenomena in their vicinity, are complicated. Many studies on the flow filed around the elastic moving airfoil have been investigated by experimental and numerical approached. The macro scale vortex structure and the dynamic forces acting on the elastic moving airfoil have been understood. However, the growth process of the vorticity in a vicinity of the wall of an elastic airfoil has not been clarified sufficiently. In this study, the authors focus on the dynamic behaviors of vorticity in the vicinity of the wall on the elastic heaving airfoil and investigate the growth process of the vorticity in a vicinity of the wall of an elastic airfoil by the fluid structure interaction and LES simulations using ANSYS 17.0/ANSYS CFX 17.0. The vorticity in the vicinity of a wall of the elastic airfoil spreads along the wall simultaneously with the increase of the spatial gradient of the wall, and discrete vorticity regions coalesce into a single layer. The time variation in spatial gradient contribute greatly to the growth and development of vorticity.

Effects of Rotating Blade Wakes on Separation and Pressure Recovery in Turbine Exhaust Diffusers

2008 ◽  
Author(s):  
Olaf Sieker ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
High Energy ◽  
Flow Coefficient ◽  
Pressure Recovery ◽  
High Mass ◽  
Scale Model ◽  
Swirl Number ◽  
Annular Diffuser ◽  
Bladed Rotor ◽  
Turbine Exhaust

Highly efficient turbine exhaust diffusers can only be designed by taking into account the unsteady interactions with the last rotating row of the turbine. Therefore, a scale model of a typical gas turbine exhaust diffuser consisting of an annular and a conical diffuser is investigated experimentally. To investigate the influence of rotating wakes, a variable-speed rotating spoke wheel with cylindrical spokes as well as with NACA bladed spokes generates high-energy turbulent wakes simulating turbine rotor wakes. For the rotor with the NACA blades, the drive of the wheel is run in motor as well as in generator mode. Additional measurements in a reference configuration without a spoke wheel allow the detailed analysis of changes in the flow pattern. 3-hole pneumatic probes, static pressure taps, as well as a 2D-Laser-Doppler-Velocimeter (LDV) are used to investigate velocity profiles and turbulent characteristics. Without the wakes generated by a spoke wheel, the annular diffuser (with a 20° half cone opening angle) separates at the shroud for all swirl configurations. Increasing the swirl results in increasing pressure recovery at the shroud whereas the hub boundary is destabilized. For a non-rotating spoke rotor and low swirl numbers, the 20° annular diffuser separates at the shroud. Increasing the swirl number, a strong deceleration of the axial velocity at the shroud is generated without separation and a higher pressure recovery is achieved. The boundary layer at the shroud of the 20° annular diffuser separates for all operating points with the bladed rotor. A partly stabilized 20° annular diffuser can only be achieved for much higher values of the flow coefficient than that for the design point. At this high mass flow, the NACA-bladed rotor operates as a turbine, resulting in the generator mode of the electric drive. Contrary to the numerical design calculations, the flow at the shroud of a 15° annular diffuser does not separate for all swirl configurations in the experiment. Pressure recovery of the 15° annular diffuser can be increased by increasing the inlet swirl whereas the hub boundary layer is destabilized. For the NACA bladed rotor, the flow in the 15° annular diffuser as well as the pressure recovery strongly depend on the flow coefficient. For flow coefficients lower than the design value, the flow partly separates at the shroud whereas large flow coefficients result in increased pressure recovery. The pressure recovery also depends on the direction of swirl and thus the swirl number.

Computational modelling and analysis of haemodynamics in a simple model of aortic stenosis

2018 ◽  
Vol 851 ◽  
pp. 23-49 ◽  
Author(s):  
Chi Zhu ◽  
Jung-Hee Seo ◽  
Rajat Mittal
Keyword(s):  
Simple Model ◽  
Aortic Stenosis ◽  
Secondary Flow ◽  
Pressure Fluctuation ◽  
Computational Modelling ◽  
Maximum Pressure ◽  
Cardiac Auscultation ◽  
Curved Pipe ◽  
Free Jet ◽  
Wall Pressure Fluctuation

In a study motivated by considerations associated with heart murmurs and cardiac auscultation, numerical simulations are used to analyse the haemodynamics in a simple model of an aorta with an aortic stenosis. The aorta is modelled as a curved pipe with a$180^{\circ }$turn, and three different stenoses with area reductions of 50 %, 62.5 % and 75 % are examined. A uniform steady inlet velocity with a Reynolds number of 2000 is used for all of the cases and direct numerical simulation is employed to resolve the dynamics of the flow. The poststenotic flow is dominated by the jet that originates from the stenosis as well as the secondary flow induced by the curvature, and both contribute significantly to the flow turbulence. On the anterior surface of the modelled aorta, the location with maximum pressure fluctuation, which may be considered as the source location for the murmurs, is found to be located around$60^{\circ }$along the aortic arch, and this location is relatively insensitive to the severity of the stenosis. For all three cases, this high-intensity wall pressure fluctuation includes contributions from both the jet and the secondary flow. Spectral analysis shows that for all three stenoses, the Strouhal number of the vortex shedding of the jet shear layer is close to 0.93, which is higher than the shedding frequency of a corresponding free jet or a jet confined in a straight pipe. This frequency also appears in the pressure spectra at the location postulated as the source of the murmurs, in the form of a ‘break frequency.’ The implications of these findings for cardiac auscultation-based diagnosis of aortic stenosis are also discussed.

Secondary Flow Loss Reduction Method by Use of Endwall Contouring in Gas Turbine Cascade Using Optimization Method

2021 ◽  
Author(s):  
Kazuki Yamamoto ◽  
Ryota Uehara ◽  
Shohei Mizuguchi ◽  
Masahiro Miyabe
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Cross Flow ◽  
Internal Flow ◽  
Optimization Method ◽  
Loss Reduction ◽  
Turbine Cascade ◽  
Flow Loss ◽  
Endwall Contouring

Abstract High efficiency is strongly demanded for gas turbines to reduce CO2 emissions. In order to improve the efficiency of gas turbines, the turbine inlet temperature is being raised higher. In that case, the turbine blade loading is higher and secondary flow loss becomes a major source of aerodynamic losses due to the interaction between the horseshoe vortex and the strong endwall cross flow. One of the authors have optimized a boundary layer fence which is a partial vane to prevent cross-flow from pressure-side to suction-side between blade to blade. However, it was also found that installing the fence leads to increase another loss due to tip vortex, wake and viscosity. Therefore, in this paper, we focused on the endwall contouring and the positive effect findings from the boundary layer fence were used to study its optimal shape. Firstly, the relationship between the location of the endwall contouring and the internal flow within the turbine cascade was investigated. Two patterns of contouring were made, one is only convex and another is just concave, and the secondary flow behavior of the turbine cascade was investigated respectively. Secondly, the shape was designed and the loss reduction effect was investigated by using optimization method. The optimized shape was manufactured by 3D-printer and experiment was conducted using cascade wind tunnel. The total pressure distributions were measured and compared with CFD results. Furthermore, flow near the endwall and the internal flow of the turbine cascade was experimentally visualized. The internal flow in the case of a flat wall (without contouring), with a fence, and with optimized endwall contouring were compared by experiment and CFD to extract the each feature.

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