Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2010 ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Aerodynamic Pressure ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage is studied. Fully unsteady, three-dimensional numerical simulations are performed using the commercial code ANSYS-CFX The numerical model is critically evaluated against experimental data. Measurements were performed with a three-dimensional fast-response aerodynamic pressure probe in the closed-loop test rig operating in the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). An analysis is first reported about the strategy to reduce the CPU and memory requirements while performing three-dimensional simulations of stator-rotor interaction in actual turbomachinery. What emerges as the best choice, at least for subsonic stages, is to simulate the unsteady behaviour of the rotor blade row alone by applying the stator outlet flow field as rotating inlet boundary condition. When measurements are available upstream of the rotor the best representation of the experimental results downstream of the stage is achieved. The agreement with the experiments achieved at the rotor exit makes the CFD simulation a key-tool for the comprehension and the interpretation of the physical mechanisms acting inside the rotor channel (often difficult to achieve using experiments only). Numerical investigations have been carried out by varying the incidence at the vane entrance. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator. The configuration is chosen is such a way to isolate the effects of the vortex-blade interaction. Results show that some general trends can be recognized in the vortex-blade interaction. The sense of rotation and the spanwise position of the incoming vortices play a crucial role on their interaction with the rotor vortices, thus determining both the time-mean and the time-resolved characteristics of the stage-exit secondary field.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Time Resolved ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Three Dimensional Clocking Effects in a One and a Half Stage Transonic Turbine

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
O. Schennach ◽  
J. Woisetschläger ◽  
B. Paradiso ◽  
G. Persico ◽  
P. Gaetani
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Fast Response ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Time Resolved ◽  
Flow Angle ◽  
Aerodynamic Pressure ◽  
Velocity Flow ◽  
Transonic Turbine

This paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three-dimensional aerodynamics of the second vane for different clocking positions. To give an overview of the time-averaged flow field, five-hole probe measurements were performed upstream and downstream of the second stator. Furthermore in these planes additional unsteady measurements were carried out with laser Doppler velocimetry in order to record rotor phase-resolved velocity, flow angle, and turbulence distributions at two different clocking positions. In the planes upstream of the second vane, the time-resolved pressure field has been measured by means of a fast response aerodynamic pressure probe. This paper shows that the secondary flows of the second vane are significantly modified by the different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out, and a 0.6% variation in the second vane loss coefficient has been recorded among the different clocking positions.

Blade Row Interaction in a One and a Half Stage Transonic Turbine Focusing on Three Dimensional Effects: Part II—Clocking Effects

2008 ◽  
Author(s):  
O. Schennach ◽  
B. Paradiso ◽  
G. Persico ◽  
P. Gaetani ◽  
J. Woisetschla¨ger
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Three Dimensional ◽  
Field Measurements ◽  
Fast Response ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Flow Angle ◽  
Aerodynamic Pressure ◽  
Transonic Turbine

The paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three dimensional flow field downstream of the high pressure turbine for different vane clocking positions. To give an overview of the time averaged flow field, measurements by means of a pneumatic five hole probe were performed upstream and downstream of the second stator. Furthermore in this planes additional unsteady measurements were carried out with Laser Doppler Velocimetry in order to record rotor phase resolved velocity, flow angle and turbulence distributions at two different clocking positions. In the measurement plane upstream the second vane the time resolved pressure field has been analyzed by means of a Fast Response Aerodynamic Pressure Probe. The paper shows that the secondary flows of the second vane are significantly modified for different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out.

Structures and Dynamics Committee Best Paper of 1996 Award: Inlet Distortion Generated Forced Response of a Low-Aspect-Ratio Transonic Fan

1997 ◽  
Vol 119 (4) ◽  
pp. 665-676 ◽  
Author(s):  
S. R. Manwaring ◽  
D. C. Rabe ◽  
C. B. Lorence ◽  
A. R. Wadia
Keyword(s):  
Aspect Ratio ◽  
Steady Flow ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Forced Response ◽  
Navier Stokes ◽  
Surface Boundary ◽  
Unsteady Pressure ◽  
Low Aspect Ratio ◽  
Transonic Fan

This paper describes a portion of an experimental and computational program (ADLARF), which incorporates, for the first time, measurements of all aspects of the forced response of an airfoil row, i.e., the flow defect, the unsteady pressure loadings, and the vibratory response. The purpose of this portion was to extend the knowledge of the unsteady aerodynamics associated with a low-aspect-ratio transonic fan where the flow defects were generated by inlet distortions. Measurements of screen distortion patterns were obtained with total pressure rakes and casing static pressures. The unsteady pressure loadings on the blade were determined from high response pressure transducers. The resulting blade vibrations were measured with strain gages. The steady flow was analyzed using a three-dimensional Navier–Stokes solver while the unsteady flow was determined with a quasi-three-dimensional linearized Euler solver. Experimental results showed that the distortions had strong vortical, moderate entropic, and weak acoustic parts. The three-dimensional Navier–Stokes analyses showed that the steady flow is predominantly two-dimensional, with radially outward flow existing only in the blade surface boundary layers downstream of shocks and in the aft part of the suction surface. At near resonance conditions, the strain gage data showed blade-to-blade motion variations and thus, linearized unsteady Euler solutions showed poorer agreement with the unsteady loading data than comparisons at off-resonance speeds. Data analysis showed that entropic waves generated unsteady loadings comparable to vortical waves in the blade regions where shocks existed.

A Parametric Study of the Blade Row Interaction in a High Pressure Turbine Stage

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
G. Persico ◽  
P. Gaetani ◽  
C. Osnaghi
Keyword(s):  
High Pressure ◽  
Strong Dependence ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Mixing Rate ◽  
Aerodynamic Pressure ◽  
Blade Row ◽  
Blade Row Interaction

An extensive experimental analysis on the subject of the unsteady periodic flow in a high subsonic high pressure (HP) turbine stage has been carried out at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). In this paper the aerodynamic blade row interaction in HP turbines, enforced by increasing the stator and rotor blade loading and by reducing the stator-rotor axial gap, is studied in detail. The time-averaged three-dimensional flowfield in the stator-rotor gap was investigated by means of a conventional five-hole probe for the nominal (0 deg) and highly positive (+22 deg) stator incidences. The evolution of the viscous flow structures downstream of the stator is presented to characterize the rotor incoming flow. The blade row interaction was evaluated on the basis of unsteady aerodynamic measurements at the rotor exit, performed with a fast-response aerodynamic pressure probe. Results show a strong dependence of the time-averaged and phase-resolved flowfield and of the stage performance on the stator incidence. The structure of the vortex-blade interaction changes significantly as the magnitude of the rotor-inlet vortices increases, and very different residual traces of the stator secondary flows are found downstream of the rotor. On the contrary, the increase in rotor loading enhances the unsteadiness in the rotor secondary flows but has a little effect on the vortex-vortex interaction. For the large axial gap, a reduction of stator-related effects at the rotor exit is encountered when the stator incidence is increased as a result of the different mixing rate within the cascade gap.

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2005 ◽  
Vol 128 (1) ◽  
pp. 11-22 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes and miniature pneumatic five-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2004 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes (FRAP) and miniature pneumatic 5-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

scholarly journals Spatial and temporal resolution of a fast-response aerodynamic pressure probe in grid-generated turbulence

2021 ◽  
Vol 62 (2) ◽  
Author(s):  
Florian M. Heckmeier ◽  
Stefan Hayböck ◽  
Christian Breitsamter
Keyword(s):  
Temporal Resolution ◽  
Pressure Sensors ◽  
Mesh Size ◽  
Reynolds Numbers ◽  
Fast Response ◽  
Pressure Probe ◽  
Aerodynamic Pressure ◽  
Kolmogorov Length Scale ◽  
High Bandwidth ◽  
Velocity Spectra

Abstract The spatial and temporal resolution of a fast-response aerodynamic pressure probe (FRAP) is investigated in a benchmark flow of grid-generated turbulence. A grid with a mesh size of $$M=6.4$$ M = 6.4 mm is tested for two different free-stream velocities, hence, resulting in Reynolds numbers of $$Re_M= \{4300,12800\}$$ R e M = { 4300 , 12800 } . A thorough analysis of the applicability of the underlying assumptions with regard to turbulence isotropy and homogeneity is carried out. Taylor’s frozen turbulence hypothesis is assumed for the calculation of deducible flow quantities, like the turbulent kinetic energy or the dissipation rate. Furthermore, besides the examination of statistical quantities, velocity spectra of measurements downstream of the grid are quantified. Results of a small fast-response five-hole pressure probe equipped with piezo-resistive differential pressure sensors are compared to single-wire hot-wire constant temperature anemometry data for two different wire lengths. Estimates of temporal and spatial turbulent scales (e.g., Taylor micro scale and Kolmogorov length scale) show good agreement to data in the literature but are affected by filtering effects. Especially in the energy spectra, very high bandwidth content cannot be resolved by the FRAP, which is mainly due to bandwidth limits in the temporal calibration of the FRAP and the minimal resolution of the integrated sensors. Graphic abstract

Calculation of the Rise and Pitch of a Three-Dimensional Low-Aspect-Ratio Flat Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 314-324
Author(s):  
Todd McComb
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Static Case ◽  
Equilibrium Flow ◽  
Low Aspect Ratio ◽  
Fast Speed ◽  
Flow Past

Using low-aspect-ratio flat ship theory, this paper defines a procedure to determine the position of a hull which is in equilibrium at some "fast" speed in terms of a given hull shape for the same hull at rest. This procedure is then used to find the equilibrium flow past a moving ship, when given the shape of the hull at rest. The method is then extended to find the hull configuration at various speeds based on either the configuration in the static case or at some other equilibrium speed, leading to a calculation of drag versus speed. Some general formulas and some simple examples are given.

Sign in / Sign up

Export Citation Format

Share Document