Time-Accurate Euler Simulation of Interaction of Nozzle Wake and Secondary Flow With Rotor Blade in an Axial Turbine Stage Using Nonreflecting Boundary Conditions

1996 ◽  
Vol 118 (4) ◽  
pp. 663-678 ◽  
Author(s):  
S. Fan ◽  
B. Lakshminarayana
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Rotor Blade ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Turbine Stage ◽  
Unsteady Pressure ◽  
Nonreflecting Boundary Conditions

The objective of this paper is to investigate the three-dimensional unsteady flow interactions in a turbomachine stage. A three-dimensional time-accurate Euler code has been developed using an explicit four-stage Runge–Kutta scheme. Three-dimensional unsteady nonreflecting boundary conditions are formulated at the inlet and the outlet of the computational domain to remove the spurious numerical reflections. The three-dimensional code is first validated for two-dimensional and three-dimensional cascades with harmonic vortical inlet distortions. The effectiveness of the nonreflecting boundary conditions is demonstrated. The unsteady Euler solver is then used to simulate the propagation of nozzle wake and secondary flow through the rotor and the resulting unsteady pressure field in an axial turbine stage. The three-dimensional and time-dependent propagation of nozzle wakes in the rotor blade row and the effects of nozzle secondary flow on the rotor unsteady surface pressure and passage flow field are studied. It was found that the unsteady flow field in the rotor is highly three dimensional and the nozzle secondary flow has significant contribution to the unsteady pressure on the blade surfaces. Even though the steady flow at the midspan is nearly two dimensional, the unsteady flow is three dimensional and the unsteady pressure distribution cannot be predicted by a two-dimensional analysis.

Time Accurate Euler Simulation of Interaction of Nozzle Wake and Secondary Flow With Rotor Blade in an Axial Turbine Stage Using Nonreflecting Boundary Conditions

1995 ◽  
Author(s):  
S. Fan ◽  
B. Lakshminarayana
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Rotor Blade ◽  
Three Dimensional ◽  
Computational Domain ◽  
Turbine Stage ◽  
Axial Turbine ◽  
Unsteady Pressure

The objective of this paper is to investigate the three dimensional unsteady flow interactions in a turbomachine stage. A three-dimensional time accurate Euler code has been developed using an explicit four-stage Runge-Kutta scheme. Three-dimensional unsteady non-reflecting boundary conditions are formulated at the inlet and at the outlet of the computational domain to remove the spurious numerical reflections. The three-dimensional code is first validated for 2-D and 3-D cascades with harmonic vortical inlet distortions. The effectiveness of non reflecting boundary conditions is demonstrated. The unsteady Euler solver is then used to simulate the propagation of nozzle wake and secondary flow through rotor and the resulting unsteady pressure field in an axial turbine stage. The three dimensional and time dependent propagation of nozzle wakes in the rotor blade row and the effects of nozzle secondary flow on the rotor unsteady surface pressure and passage flow field are studied. It was found that the unsteady flow field in the rotor is highly three-dimensional and the nozzle secondary flow has significant contribution to the unsteady pressure on the blade surfaces. Even though the steady flow at the midspan is nearly two-dimensional, the unsteady flow is 3-D and the unsteady pressure distribution can not by predicted by a 2-D analysis.

scholarly journals Experimental Study of a 3D Wake Decay and Secondary Flows Behind a Rotor Blade Row of a Low Speed Compressor Stage

1996 ◽  
Author(s):  
A. S. Witkowski ◽  
T. J. Chmielniak ◽  
M. D. Strozik
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Rotor Blade ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Compressor Stage ◽  
Blade Row

Detailed measurements have been performed in a low pressure axial flow compressor stage to investigate the structure of the secondary flow field and the three-dimensional wake decay at different axial locations before and behind the rotor. The three dimensional flow field upstream and downstream of the rotor and on the centerline of the stator blade passage have been sampled periodically using a straight and a 90 degree triple-split fiber probe. Radial measurements at 39 radial stations were carried out at chosen axial positions in order to get the span-wise characteristics of the unsteady flow. Taking the experimental values of the unsteady flow velocities and turbulence properties, the effects of the rotor blade wake decay and secondary flow on the blade row spacing and stator passage flow at different operating conditions are discussed. For the normal operating point, the component of radial turbulent intensities in the leakage-flow mixing region is found to be much higher than the corresponding axial and tangential components. But for a higher value of the flow coefficient the relations are different.The results of the experiments show that triple-split fiber probes, straight and 90 degree measurements, combined with the ensemble average technique are a very useful method for the analysis of rotor flow in turbomachinery. Tip clearance vortex, secondary flow near the hub and radial flow in the wake, turbulent intensity and Reynolds stresses and also the decay of the rotor wakes can be obtained by this method.

scholarly journals Endwall and Unsteady Flow Phenomena in an Axial Turbine Stage

1994 ◽  
Author(s):  
H. E. Gallus ◽  
J. Zeschky ◽  
C. Hah
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Radial Distribution ◽  
Three Dimensional ◽  
Hot Wire ◽  
Turbine Stage ◽  
Flow Properties ◽  
Blade Row ◽  
Secondary Flow Field

Detailed experimental and numerical studies have been performed in a subsonic, axial-flow turbine stage to investigate the secondary flow field, the aerodynamic loss generation, and the spanwise mixing under a stage environment. The experimental study includes measurements of the static pressure distribution on the rotor blade surface and the rotor exit flow field using three-dimensional hot-wire and pneumatic probes. The rotor exit flow field was measured with an unsteady hot-wire probe which has high temporal and spatial resolution. Both steady and unsteady numerical analyses were performed with a three-dimensional Navier-Stokes code for the multiple blade rows. Special attention was focused on how well the steady multiple-blade-row calculation predicts the rotor exit flow field and how much the blade interaction affects the radial distribution of flow properties at the stage exit. Detailed comparisons between the measurement and the steady calculation indicate that the steady multiple-blade-row calculation predicts the overall time-averaged flow field very well. However, the steady calculation does not predict the secondary flow at the stage exit accurately. The current study indicates that the passage vortex near the hub of the rotor is transported toward the mid-span due to the blade interaction effects. And, the structure of the secondary flow field at the exit of the rotor is significantly modified by the unsteady effects. The time-averaged secondary flow field and the radial distribution of the flow properties, which are uses for the design of the following stage, can be predicted more accurately with the unsteady flow calculation.

Endwall and Unsteady Flow Phenomena in an Axial Turbine Stage

1995 ◽  
Vol 117 (4) ◽  
pp. 562-570 ◽  
Author(s):  
H. E. Gallus ◽  
J. Zeschky ◽  
C. Hah
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Radial Distribution ◽  
Three Dimensional ◽  
Hot Wire ◽  
Turbine Stage ◽  
Flow Properties ◽  
Blade Row ◽  
Secondary Flow Field

Detailed experimental and numerical studies have been performed in a subsonic, axial-flow turbine stage to investigate the secondary flow field, the aerodynamic loss generation, and the spanwise mixing under a stage environment. The experimental study includes measurements of the static pressure distribution on the rotor blade surface and the rotor exit flow field using three-dimensional hot-wire and pneumatic probes. The rotor exit flow field was measured with an unsteady hot-wire probe, which has high temporal and spatial resolution. Both steady and unsteady numerical analyses were performed with a three-dimensional Navier–Stokes code for the multiple blade rows. Special attention was focused on how well the steady multiple-blade-row calculation predicts the rotor exit flow field and how much the blade interaction affects the radial distribution of flow properties at the stage exit. Detailed comparisons between the measurement and the steady calculation indicate that the steady multiple-blade-row calculation predicts the overall time-averaged flow field very well. However, the steady calculation does not predict the secondary flow at the stage exit accurately. The current study indicates that the passage vortex near the hub of the rotor is transported toward the midspan due to the blade interaction effects. Also, the structure of the secondary flow field at the exit of the rotor is significantly modified by the unsteady effects. The time-averaged secondary flow field and the radial distribution of the flow properties, which are used for the design of the following stage, can be predicted more accurately with the unsteady flow calculation.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

Numerical Simulation of Viscous Flow-Field in Cascade Using Thin-Layer Equations and AF Method

1999 ◽  
Author(s):  
Yumin Xiao ◽  
R. S. Amano
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Viscous Flow ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Factorization Method ◽  
Computational Domain ◽  
Approximate Factorization ◽  
Calculation Results ◽  
Transonic Cascade

Abstract In this paper an implicit 3-D solver for computations of a viscous flow has been developed and the computations of the flow between blade passage are presented. This method employs an AF (Approximate Factorization) method in which four techniques are incorporated to speed up convergence to the steady-state solutions: (1) body-fitted H-grid; (2) artificial viscosity; (3) implicit residual smoothing; and (4) local time-stepping. The two-dimensional pseudo-characteristic method was used to determine the inlet and outlet boundary conditions of the computational domain and the periodic boundary conditions were used at inter-boards. The validation cases include subsonic and transonic viscous flows in C3X cascade. Results for these turbine cascade flows are presented and compared with experiments at corresponding conditions. Computed pressure distributions on blade surfaces show good agreement with the published experimental data. This method was further applied to a three-dimensional case and demonstrated the code capability for predicting the secondary flow in a 3-D transonic flow-field. From these computations it was found that the proposed method possesses superior convergence characteristics and can be extended to unsteady flow calculations. Finally, it was observed that the three-dimensional calculation results show that the secondary flow mechanism in a transonic cascade seems to be quit different from those, in a subsonic case.

Unsteady Interactions Between Axial Turbine and Nonaxisymmetric Exhaust Hood Under Different Operational Conditions

2011 ◽  
Vol 134 (4) ◽  
Author(s):  
Jing-Lun Fu ◽  
Jian-Jun Liu ◽  
Si-Jing Zhou
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Exhaust System ◽  
Single Stage ◽  
Exhaust Hood ◽  
Turbine Stage ◽  
Axial Turbine ◽  
Operational Conditions ◽  
Flow Interactions

The exhaust system in condensing steam turbines is used to recover leaving kinetic energy of the last stage turbine, while guiding the flow from turbine to condenser. The flows in the exhaust system and the turbine stage are fully coupled and inherently unsteady. The unsteady flow interactions between the turbine and the exhaust system have a strong impact on the blade loading or blade aerodynamic force. This paper describes the unsteady flow interactions between a single-stage axial turbine and an exhaust system. The experimental and numerical studies on the coupled flow field in the single-stage turbine and the exhaust hood model under different operational conditions have been carried out. Unsteady pressure at the turbine rotor blade, turbine outlet, and exhaust outcasing are measured and compared with the numerical prediction. The details of unsteady flow in the exhaust system with the whole annulus stator and rotor blade rows are simulated by employing the computational fluid dynamics software CFX-5. Results show that for the investigated turbine-exhaust configuration the influence of the flow field in the exhaust system on the unsteady blade force is much stronger than that of the stator and rotor interaction. The flow pattern in the exhaust system changes with the turbine operational condition, which influences the unsteady flow in the turbine stage further.

Investigation of the Unsteady Rotor Aerodynamics in a Transonic Turbine Stage

2000 ◽  
Vol 123 (1) ◽  
pp. 81-89 ◽  
Author(s):  
R. De´nos ◽  
T. Arts ◽  
G. Paniagua ◽  
V. Michelassi ◽  
F. Martelli
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Unsteady Flow ◽  
Rotational Speed ◽  
Pressure Field ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Rotor Aerodynamics ◽  
Transonic Turbine

The paper focuses on the unsteady pressure field measured around the rotor midspan profile of the VKI Brite transonic turbine stage. The understanding of the complex unsteady flow field is supported by a quasi-three-dimensional unsteady Navier–Stokes computation using a k-ω turbulence model and a modified version of the Abu-Ghannam and Shaw correlation for the onset of transition. The agreement between computational and experimental results is satisfactory. They both reveal the dominance of the vane shock in the interaction. For this reason, it is difficult to identify the influence of vane-wake ingestion in the rotor passage from the experimental data. However, the computations allow us to draw some useful conclusions in this respect. The effect of the variation of the rotational speed, the stator–rotor spacing, and the stator trailing edge coolant flow ejection is investigated and the unsteady blade force pattern is analyzed.

Reduction of Turbine Blade Unsteady Forces by Shape Modification of Vanes for Industrial Gas Turbines

2016 ◽  
Author(s):  
Xiying Niu ◽  
Lin Wang ◽  
Dongming Li ◽  
Qiuli Du
Keyword(s):  
Unsteady Flow ◽  
Turbine Blade ◽  
Rotor Blade ◽  
Static Pressure ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Leading Edge ◽  
Turbine Stage ◽  
Shape Modification ◽  
Unsteady Forces

The flow in turbomachinery is inherently three-dimensional unsteady and turbulent. Unsteady factors due to the viscous wakes and potential effects of blades, affect the blade surface pressure distribution, which leads to blade vibrations by periodic pulsating flow forces. While the aerodynamic excitation frequency equals to the natural frequency of blades, critical blade vibrations are excited, which could lead to a reduction of lifetime or even a destruction of rotor blades. Although a large number of investigations about turbine unsteady flow fields and unsteady excitation forces have been carried out, these investigations do not focus on how to reduce the turbine blade unsteady forces. In this article, the turbine stators were redesigned by forward-swept and positive-leaned vanes, in order to reduce the blade excitation forces. And, the swept angles and leaned angles are determined respectively, that is, the vane is forward swept 3 degree, and positive leaned 13 degree, with the purpose of ensuring that while the hub exit flow of a vane aligns with the leading edge of one downstream rotor blade, the tip exit flow could align with the leading edge of another rotor blade that is adjacent to the above rotor blade pressure side. Comparative investigations into the turbine unsteady flow fields between the redesigned and original cases are performed by using a three-dimensional Navier-Stokes viscous solver. Emphasis is placed on how the vane modification reduces the turbine blade unsteady forces. The results indicate that the static pressure fluctuation at vane trailing edge region is reduced compared to the baseline, and high loss region inside vane passages is also reduced. Besides, blade-to-blade entropy distribution of the turbine stage shows that, the vane wake width is reduced by its shape modification, especially at 5% and 95% span. Due to these, the temporal-spatial profile of rotor blade static pressure coefficient shows that, the unsteady fluctuation of rotor blade becomes weak obviously for the redesigned case. Overall, compared to the baseline, on the condition that the mass flowrate and expansion ratio are nearly the same, the torque fluctuation is reduced from 12.78% to 6.92%, and the axial force fluctuation is reduced from 8.82% to 6.51%, which not only is good for reducing the stream exciting force, but also can make the output power more stable. And, the turbine stage time-averaged efficiency increases slightly by 0.18%. Detailed results about static pressure coefficient distributions, entropy distributions, torque and axial forces are presented and discussed in the paper.

Clocking Effects in a 1.5 Stage Axial Turbine—Steady and Unsteady Experimental Investigations Supported by Numerical Simulations

2001 ◽  
Vol 124 (1) ◽  
pp. 52-60 ◽  
Author(s):  
U. Reinmo¨ller ◽  
B. Stephan ◽  
S. Schmidt ◽  
R. Niehuis
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Energy Transport ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Field Measurements ◽  
Experimental Investigations ◽  
Axial Turbine ◽  
Outlet Flow

The interaction between rotor and stator airfoils in a multistage turbomachine causes an inherently unsteady flow field. In addition, different relative circumferential positions of several stator rows and rotor rows, respectively, have an influence on the flow behavior in terms of loss generation, energy transport and secondary flow. The objective of the presented study is to investigate the effects of stator airfoil clocking on the performance of a 1-1/2 stage axial cold air turbine. The investigated axial turbine consists of two identical stators. The low aspect ratio of the blades and their prismatic design leads to a three-dimensional outlet flow with a high degree of secondary flow phenomena. Nevertheless, the small axial gaps between the blade rows are responsible for strong potential flow interaction with the radial wake regions in the measurement planes. Consequently, parts of the wakes of the first stator are clearly detected in the rotor outlet flow. To give an overview of the time-averaged flow field, measurements with pneumatic probes are conducted behind each blade row at ten different clocking-positions of the second stator. Further, an optimized clocking position was found due to a minimum in pressure loss behind the second stator. The unsteady measurements are carried out with hot-wire probes for three selected stator-stator positions. Animations of selected flow properties show the influence of different circumferential positions of the second stator on the unsteady flow behavior and secondary flow field. In addition and compared with experimental results three-dimensional unsteady viscous flow computations are performed.

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