Aerodynamic Damping Predictions for Oscillating Airfoils in Cascades Using Moving Meshes

2016 ◽  
Author(s):  
Ron Ho Ni ◽  
William Humber ◽  
Michael Ni ◽  
Vincent R. Capece ◽  
Michael Ooten ◽  
...  
Keyword(s):  
Experimental Data ◽  
Numerical Solutions ◽  
Harmonic Balance Method ◽  
Standard Test ◽  
Influence Coefficient ◽  
Flow Conditions ◽  
Suction Surface ◽  
Test Configuration ◽  
Aerodynamic Loading ◽  
Unsteady Aerodynamic

This paper presents a numerical analysis of oscillating airfoils in turbomachinery cascades using the unsteady nonlinear Reynold’s Averaged Navier-Stokes (URANS) equations. The periodic unsteady flow solutions are determined using a conventional time marching method (DTS) and the Nonlinear Harmonic Balance method (NHB). Mesh motions, using a weighted distortion procedure and a linear elastic method, are described. Comparison of computed results are made with the Eleventh Standard Test Configuration (STC11) experimental data for subsonic and transonic exit flow conditions. The solutions for the NHB and DTS methods exhibit excellent correlation with each other and good correlation with the experimental data on the pressure surface. The numerical solutions deviate from the experimental data on the suction surface especially in the vicinity of the shock wave for the transonic exit flow case. A numerical influence coefficient modeling method is shown for airfoil cascades that can be used to calculate unsteady aerodynamic loading over a range of interblade phase angles. Application to the STC11 illustrates that a cascade of five airfoils is sufficient to provide accurate unsteady aerodynamic loading predictions for the modeled flow conditions.

scholarly journals Analysis of Experimental Time-Dependent Blade Surface Pressures From an Oscillating Turbine Cascade With the Influence-Coefficient Technique

1990 ◽  
Author(s):  
T. H. Fransson
Keyword(s):  
Experimental Data ◽  
Leading Edge ◽  
Travelling Wave ◽  
Time Dependent ◽  
Influence Coefficient ◽  
Blade Surface ◽  
Suction Surface ◽  
Local Flow ◽  
Unsteady Aerodynamic ◽  
Influence Coefficients

A two-dimensional section of the last stage of a steam turbine has been investigated experimentally in an annular non-rotating cascade facility as regards to its steady-state and time-dependent aerodynamic characteristics at design and off-design conditions. The unsteady experimental data obtained with the blades vibrating in the “travelling wave” mode indicate that one of the main reasons for the flutter susceptibility of the cascade lies in the high expansion and following shock wave close to the blade suction surface leading edge and the corresponding high unsteady loading. The decomposition of the experimental data into unsteady aerodynamic influence coefficients validates this conclusion and gives also that another reason for the flutter susceptibility can be found in the fact that the cascade is overlapped for a part of the blade surface where the local flow velocities are close to sonic. The unsteady aerodynamic influence coefficients show that the instability arises because of the time dependent aerodynamic coupling effects between, essentially, the reference blade and its immediate suction surface and, to a lesser extent, pressure surface neighbors.

scholarly journals Aerodynamic Damping Characteristics of a Transonic Turbine Cascade

1999 ◽  
Author(s):  
Mizuho Aotsuka ◽  
Toshinori Watanabe ◽  
Yasuo Machida
Keyword(s):  
Phase Angle ◽  
Aerodynamic Force ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Influence Coefficient ◽  
Suction Surface ◽  
Aerodynamic Damping ◽  
Unsteady Aerodynamic ◽  
Design Case ◽  
Oscillation Instability

The unsteady aerodynamic characteristics of oscillating thin turbine blades were studied both experimentally and numerically to obtain the comprehensive knowledge on the aerodynamic damping of the blades operating in transonic flows. The experiment was carried out in a linear cascade tunnel by use of the influence coefficient method. The two flow conditions were adopted, namely, a near-design condition and an off-design condition with a higher back pressure. In the results for the near-design case, a strong vibration instability was observed in the positive side of the interblade phase angle. In the off-design case, however, the instability did not appear for almost all the interblade phase angles. A drastic change was found in the phase angle of unsteady aerodynamic force between the two cases, which change was a governing factor for the oscillation instability. Numerical simulation based on 2-D Euler equation revealed that the phase change came from the change in phase of the unsteady surface pressure across the shock impingement point on the blade suction surface in the off-design case. The numerical results also showed that the aerodynamic damping increased with increasing reduced frequency, and that the oscillation instability disappeared.

Experimental and Computational Study of Oscillating Turbine Cascade and Influence of Part-Span Shrouds

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
X. Q. Huang ◽  
L. He ◽  
David L. Bell
Keyword(s):  
Experimental Data ◽  
Computational Study ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Correction Method ◽  
Influence Coefficient ◽  
Turbine Cascade ◽  
Test Configuration ◽  
Practical Applications ◽  
Influence Coefficient Method

This paper presents a combined experimental and computational study of unsteady flows in a linear turbine cascade oscillating in a three-dimensional bending/flapping mode. Detailed experimental data are obtained on a seven-bladed turbine cascade rig. The middle blade is driven to oscillate and oscillating cascade data are obtained using an influence coefficient method. The numerical simulations are performed by using a 3D nonlinear time-marching Navier–Stokes flow solver. Single-passage domain computations for arbitrary interblade phase angles are achieved by using the Fourier shape correction method. Both measurements and predictions demonstrate a fully 3D behavior of the unsteady flows. The influence of the aerodynamic blockage introduced by part-span shrouds on turbine flutter has been investigated by introducing flat plate shaped shrouds at 75% span. In contrast to practical applications, in the present test configuration, the mode of vibration of the blades remains unchanged by the introduction of the part-span shroud. This allows the influence of the aerodynamic blockage introduced by the part-span shroud to be assessed in isolation from the change in mode shape. A simple shroud model has been developed in the computational solver. The computed unsteady pressures around the shrouds are in good agreement with the experimental data, demonstrating the validity of the simple shroud model. Despite of notable variations in local unsteady pressures around the shrouds, the present results show that the blade aerodynamic damping is largely unaffected by the aerodynamic blockage introduced by part-span shrouds.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

Effect of Shock Wave Behavior on Unsteady Aerodynamic Characteristics of Oscillating Transonic Compressor Cascade

2021 ◽  
Author(s):  
Jiuliang Gan ◽  
Toshinori Watanabe ◽  
Takehiro Himeno
Keyword(s):  
Shock Wave ◽  
Aerodynamic Force ◽  
Aerodynamic Characteristics ◽  
Fast Response ◽  
Influence Coefficient ◽  
Compressor Cascade ◽  
Blade Vibration ◽  
Unsteady Pressure ◽  
Transonic Compressor ◽  
Unsteady Aerodynamic

Abstract The unsteady behavior of the shock wave was studied in an oscillating transonic compressor cascade. The experimental measurement and corresponding numerical simulation were conducted on the cascade with different shock patterns based on influence coefficient method. The unsteady pressure distribution on blade surface was measured with fast-response pressure-sensitive paint (PSP) to capture the unsteady aerodynamic force as well as the shock wave movement. It was found that the movement of shock waves in the neighboring flow passages of the oscillating blade was almost anti-phase between the two shock patterns, namely, the double shocks pattern and the merged shock pattern. It was also found that the amplitude of the unsteady pressure caused by the passage shock wave was very large under the merged shock pattern compared with the double shocks pattern. The stability of blade vibration was also analyzed for both shock patterns including 3-D flow effect. These findings were thought to shed light on the fundamental understanding of the unsteady aerodynamic characteristics of oscillating cascade caused by the shock wave behavior.

Compressor Performance 2D Modelling at Reverse Flow Conditions

2010 ◽  
Author(s):  
L. Gallar ◽  
I. Tzagarakis ◽  
V. Pachidis ◽  
R. Singh
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Engine Performance ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Compressor Surge ◽  
Compressor Performance ◽  
Shaft Failure

After a shaft failure the compression system of a gas turbine is likely to surge due to the heavy vibrations induced on the engine after the breakage. Unlike at any other conditions of operation, compressor surge during a shaft over-speed event is regarded as desirable as it limits the air flow across the engine and hence the power available to accelerate the free turbine. It is for this reason that the proper prediction of the engine performance during a shaft over-speed event claims for an accurate modelling of the compressor operation at reverse flow conditions. The present study investigates the ability of the existent two dimensional algorithms to simulate the compressor performance in backflow conditions. Results for a three stage axial compressor at reverse flow were produced and compared against stage by stage experimental data published by Gamache. The research shows that due to the strong radial fluxes present over the blades, two dimensional approaches are inadequate to provide satisfactory results. Three dimensional effects and inaccuracies are accounted for by the introduction of a correction parameter that is a measure of the pressure loss across the blades. Such parameter is tailored for rotors and stators and enables the satisfactory agreement between calculations and experiments in a stage by stage basis. The paper concludes with the comparison of the numerical results with the experimental data supplied by Day on a four stage axial compressor.

scholarly journals MODELLING CHLORIDE DIFFUSION IN CONCRETE WITH INFLUENCE OF CONCRETE STRESS STATE

2017 ◽  
Vol 23 (7) ◽  
pp. 955-965 ◽  
Author(s):  
Jian WANG ◽  
Pui-Lam NG ◽  
Weishan WANG ◽  
Jinsheng DU ◽  
Jianyong SONG
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Stress State ◽  
Diffusion Model ◽  
Stress Ratio ◽  
Chloride Diffusion ◽  
Influence Coefficient ◽  
Chloride Diffusion Coefficient ◽  
Stress Influence ◽  
Concrete Stress

Under coastal or marine conditions, chloride erosion is the major accelerating factor of reinforcement corrosion. Therefore, it is of vital importance to investigate the chloride diffusion model. Research reveals that the concrete stress state has great influence on chloride diffusion; therefore a stress influence coefficient was incorporated in chloride diffusion coefficient model by many researchers. By referring to the experimental data from eight different researchers, the law between stress influence coefficient and concrete stress ratio is studied in detail, and equations relating the stress influence coefficient with the concrete stress ratio are established. Compared with three typical existing groups of equations, it is found that the proposed equations give the most accurate estim.ation of the stress influence coefficient. Hence, the proposed equations can be adopted to improve the valuation of chloride diffusion coefficient, and a modified chloride diffusion model is put forward. Three groups of experimental data are used to validate the modified chloride diffusion model, which is shown to be reasonable and having high prediction accuracy.

scholarly journals The Design and Evaluation of a 14 Stage, 16:1 Pressure Ratio Compressor for an Industrial Gas Turbine

1996 ◽  
Author(s):  
Mohammad R. Saadatmand
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Rotor Blade ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Suction Surface ◽  
Design Intent ◽  
Flow Through ◽  
Industrial Gas Turbine

The aerodynamic design process leading to the production configuration of a 14 stage, 16:1 pressure ratio compressor for the Taurus 70 gas turbine is described. The performance of the compressor is measured and compared to the design intent. Overall compressor performance at the design condition was found to be close to design intent. Flow profiles measured by vane mounted instrumentation are presented and discussed. The flow through the first rotor blade has been modeled at different operating conditions using the Dawes (1987) three-dimensional viscous code and the results are compared to the experimental data. The CFD prediction agreed well with the experimental data across the blade span, including the pile up of the boundary layer on the corner of the hub and the suction surface. The rotor blade was also analyzed with different grid refinement and the results were compared with the test data.

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