scholarly journals Investigation of the Optimum Clocking Position in a Two-Stage Axial Turbine

2005 ◽  
Vol 2005 (3) ◽  
pp. 202-210 ◽  
Author(s):  
Dieter Bohn ◽  
Sabine Ausmeier ◽  
Jing Ren
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Preliminary Design ◽  
Two Stage ◽  
Axial Turbine ◽  
Sliding Mesh ◽  
Field Distributions ◽  
Unsteady Simulation

A frozen rotor approach in a steady calculation and a sliding mesh approach in an unsteady simulation are performed in a stator clocking investigation. The clocking is executed on the second stator in a two-stage axial turbine over several circumferential positions. Flow field distributions as well as the estimated performances from two approaches are compared with each other. The optimum clocking positions are predicted based on the estimated efficiency from the two approaches. The consistence of the optimum clocking positions is discussed in the paper. The availability and the limit of the frozen rotor approach in predicting the optimum clocking position is analyzed. It is concluded that the frozen rotor approach is available to search the optimum clocking position in the preliminary design period, although it misses some features of the unsteady flow field in the multistage turbines.

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.

CFD Analysis of the Unsteady Flow in a Two-Stage Axial Turbine

2016 ◽  
Author(s):  
Yang Pan ◽  
Qi Yuan ◽  
Qian Chen ◽  
Qing Ge ◽  
Dawei Ji
Keyword(s):  
Unsteady Flow ◽  
Rotational Speed ◽  
High Speed ◽  
Stokes Equations ◽  
Great Influence ◽  
Two Stage ◽  
Lower Efficiency ◽  
Axial Turbine ◽  
Partial Admission ◽  
Mode A

Partial admission, which has the advantage of avoiding large losses while the turbine at low load operations, is widely used in regulating the power of turbomachinery. However, partial admission causes prominent unsteady flow, additional exciting forces and extra losses. Thus, it has great significance to investigate the characteristics of partial admission turbines. In this paper, efficiency and unsteady flow performance of a small two-stage subsonic axial turbine with partial admission are analyzed. Firstly, a 3-D model with four discontinuous equally-distributed nozzle blocks was built, and the computational grid, which only consisted of hexahedral mesh, was generated. Reynolds Averaged Navier-Stokes equations were solved by commercial software ANSYS-CFX and the RNG k-ε turbulence model was adopted. Secondly, to investigate the influence of admission modes, two partial admission modes (A-two diagonal valve opening; B-two adjacent valves opening) were analyzed separately and compared with the full admission situation (Mode C). Finally, the turbine performances in Mode A and B at other speeds (75% and 110% of rated speed) were analyzed and pressure distributions at three different heights (10%, 50% and 90% of the blade height) were investigated in detail. The results indicated that partial admission could cause extra mixture losses and lead to lower efficiency. Among these kinds of modes, full admission (Mode C) performed best in efficiency, and Mode B performed better than Mode A under partial admission conditions. Furthermore, strong non-uniformity was found in circumferential direction and large pressure drop occurred at the gap between two admission blocks due to expansion effects. The computational results also showed that the flow parameter fluctuations attenuated evidently in the downstream stages and the pressure vibration mainly occurred after nozzle stages. Strong vortices and backflow can be noticed at the pressure side of the active nozzle boxes. Additionally, the rotational speed has a great influence on the performance of turbine. Higher rotational speed led to bigger efficiency and smoother pressure distribution. And the alteration trend becomes slow at high speed.

The 2-Stage Axial Turbine Test Facility “LISA”

2001 ◽  
Author(s):  
M. Sell ◽  
J. Schlienger ◽  
A. Pfau ◽  
M. Treiber ◽  
R. S. Abhari
Keyword(s):  
Unsteady Flow ◽  
Mass Flow ◽  
Measurement Techniques ◽  
Operating Conditions ◽  
Test Facility ◽  
Two Stage ◽  
Axial Turbine ◽  
Aerodynamic Pressure ◽  
Second Stage ◽  
The Impact

This paper describes the design and construction of a new two stage axial turbine test facility, christened “Lisa”. The research objective of the rig is to study the impact (relevance) of unsteady flow phenomena upon the aerodynamic performance, this being achieved through the use of systematic studies of parametric changes in the stage geometry and operating point. Noteworthy in the design of the rig is the use of a twin shaft arrangement to decouple the stages. The inner shaft carries the load from the first stage whilst the outer is used with an integral torque-meter to measure the loading upon the second stage alone. This gives an accurate measurement of the loading upon the aerodynamically representative second stage, which possesses the correct stage inlet conditions in comparison to the full two stage machine which has an unrealistic axial inlet flow at the first stator. A calibrated Venturi nozzle measures the mass flow at an accuracy of below 1%, from which stage efficiencies can be derived. The rig is arranged in a closed loop system. The turbine has a vertical arrangement and is connected through a gear box to a generator system that works as a brake to maintain the desired operating speed. The turbine exit is open to ambient pressure. The rig runs at a low pressure ratio of 1.5. The maximum Mach number at stator exit is 0.3 at an inlet pressure of 1.5 bar. The maximum mass flow is 14 kg/sec. Nominal rotor design speed is 3000 RPM. The tip to hub blade ratio is 1.29, and the nominal axial chord is 50 mm. The rig is designed to accommodate a broad range of measurement techniques, but with a strong emphasis upon unsteady flow methods, for example fast response aerodynamic pressure probes for time-resolved flow measurements. The first section of this paper describes the overall test facility hardware. This is followed by a detailed focus on the torque measurement device including stage efficiency measurements at operating conditions in Lisa. Discussion of measurement techniques completes the paper.

Aerodynamic Investigation of the Performance of a Two Stage Axial Turbine at Design and Off-Design Conditions

2011 ◽  
Author(s):  
Sherif A. Abdelfattah ◽  
Hicham A. Chibli ◽  
M. T. Schobeiri
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Numerical Dissipation ◽  
Two Stage ◽  
Engine Operation ◽  
Axial Turbine ◽  
Secondary Loss ◽  
Loss Mechanisms

This paper describes numerical aerodynamic investigations of a two-stage, high pressure axial turbine at design and off-design operating conditions. The flow field in a high pressure turbine is highly complex due to unsteadiness of the flow and the various effects of blade row interaction. Blade loss mechanisms generally include primary and secondary loss mechanisms. Examples of primary loss mechanisms include boundary layer losses, shock losses and mixing losses, whereas examples of secondary losses include tip leakage losses and end wall losses which both create secondary flow characteristics. Although modern numerical analysis techniques have provided good understanding of the flow field, it is still difficult to accurately predict impact due to the aforementioned loss effects. This is generally due to errors predicting in boundary layers, transition as well as false entropy generation due to numerical dissipation. When a turbine is operated at off-design conditions the primary and secondary loss effects are further increased and create further reductions in engine efficiency. In this study a numerical model of the two-stage axial turbine was constructed and run under boundary conditions designed to mimic the operating conditions applied during engine operation. The shear stress transport (SST) turbulence model was selected for its versatility in turbomachinery applications. A comparison was made between both experimentally measured efficiencies and numerically predicted efficiencies.

Investigation of 3D Unsteady Flows in a Two Stage Shrouded Axial Turbine Using Stereoscopic PIV and FRAP: Part I — Interstage Flow Interactions

2006 ◽  
Author(s):  
L. Porreca ◽  
Y. I. Yun ◽  
A. I. Kalfas ◽  
S. J. Song ◽  
R. S. Abhari
Keyword(s):  
Flow Field ◽  
Measurement Techniques ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Fast Response ◽  
Design Flow ◽  
Main Stream ◽  
Two Stage ◽  
Axial Turbine ◽  
Improved Design

A detailed flow analysis has been carried out in a two-stage shrouded axial turbine by means of intrusive and non-intrusive measurement techniques. Multi-sensor Fast Response Aerodynamic Probe (FRAP) and 3D-PIV system were applied at two locations downstream of the first and second rotors. Several radial planes were measured focusing on the blade tip region in order to obtain a unique set of steady and unsteady velocity data. The investigation deals with the aerodynamics and kinematics of flow structures downstream of the first and second rotors and their interaction with the main flow in a partially shrouded turbine typical of industrial application. The first part of this work is focused on the flow field downstream of the first rotor while the second part studies the leakage flow in the cavity of the second rotor and its interaction with the main stream. The interstage region is characterized by interactions between the tip passage vortex and a vortex caused by the recessed shroud platform design. Flow coming from the blade passage suddenly expands and migrates radially in the cavity region causing a localized total pressure drop. The time evolution of these vortical structures and the associated downstream unsteady loss generation are analyzed. The partial shroud design adopted in this geometry is beneficial in terms of blade stress and thermal load; however flow field downstream of the first rotor is highly three dimensional due to the intense interaction between cavity and main streams. A flow interpretation is provided and suggestions for improved design are finally addressed based on the steady and unsteady flow analysis.

Numercial Simulation on Three-Dimensional Unsteady Flow in a Supercharged Boiler Gas Turbine

2012 ◽  
Vol 271-272 ◽  
pp. 1039-1043
Author(s):  
Gao Su ◽  
G.Y. Zhou ◽  
Fei Du
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Gas Turbine ◽  
Optimization Design ◽  
Three Dimensional ◽  
Aerodynamic Optimization ◽  
Axial Distribution ◽  
Sliding Mesh ◽  
Flow Field Characteristics ◽  
Fluent Software

To the unsteady characteristic of three-dimensional flow in the gas turbine blade cascades, based on sliding mesh and a standard turbulent flow model, Fluent software was employed to solve the Reynolds averaged N-S equation. The numberical result of unsteady flow field is obtained in gas turbine cascade for supercharged marine boiler. This paper shows the axial distribution of Ma in the position of β=0 in a calculational period time, and the effect of trails to flow field characteristics. The result can provide guidelines for aerodynamic optimization design of gas turbine stage cascade.

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.

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.

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

2001 ◽  
Author(s):  
U. Reinmöller ◽  
B. Stephan ◽  
S. Schmidt ◽  
R. Niehuis
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Energy Transport ◽  
Three Dimensional ◽  
Field Measurements ◽  
Flow Behaviour ◽  
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 behaviour 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 an 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 optimised clocking position was found due to a minimum in pressure loss behind the 2nd 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 behaviour and secondary flow field. In addition and compared with experimental results three-dimensional unsteady viscous flow computations are performed.

Influence of Stator Clocking on the Unsteady Three-Dimensional Flow in a Two-Stage Turbine

2005 ◽  
Vol 127 (1) ◽  
pp. 156-163 ◽  
Author(s):  
Dieter Bohn ◽  
Jing Ren ◽  
Michael Sell
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Computer Code ◽  
Navier Stokes ◽  
Two Stage ◽  
Sliding Mesh ◽  
Turbine Efficiency ◽  
Stator Vane ◽  
Outlet Flow ◽  
Time Marching

To give insight into the influence of the clocking and the stator–rotor interaction, the unsteady three-dimensional (3D) flow through a two-stage turbine is simulated numerically, using a time marching Navier–Stokes computer code with a sliding mesh approach. A stator clocking is applied to the second stator vane over several circumferential positions. The numerical results are compared with the experimental one to check the availability of the code. Clocking effects on the turbine performance, wake trajectories, and outlet flow field are focused. A relative efficiency variation of about 0.52% is concluded among clocking positions. A link between the turbine efficiency and the wake trajectories on the midspan is shown based on the presented clocking analysis in the 3D unsteady flow field. The detailed illustration of the outlet flow field shows that the influence of the clocking at the outlet is focused on the temperature distribution.

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