Wind Tunnel Wall Effects in a Linear Oscillating Cascade

1993 ◽  
Vol 115 (1) ◽  
pp. 147-156 ◽  
Author(s):  
D. H. Buffum ◽  
S. Fleeter
Keyword(s):  
Wind Tunnel ◽  
Phase Angle ◽  
Detrimental Effect ◽  
Subsonic Flow ◽  
Poor Correlation ◽  
Tunnel Wall ◽  
Unsteady Aerodynamic ◽  
Unsteady Surface Pressure ◽  
Good For ◽  
Interblade Phase Angle

Experiments in a linear oscillating cascade reveal that the wind tunnel walls enclosing the airfoils have, in some cases, a detrimental effect on the oscillating cascade aerodynamics. In a subsonic flow field, biconvex airfoils are driven simultaneously in harmonic, torsion-mode oscillations for a range of interblade phase angle values. It is found that the cascade dynamic periodicity—the airfoil-to-airfoil variation in unsteady surface pressure—is good for some values of interblade phase angle but poor for others. Correlation of the unsteady pressure data with oscillating flat plate cascade predictions is generally good for conditions where the periodicity is good and poor where the periodicity is poor. Calculations based upon linearized unsteady aerodynamic theory indicate that pressure waves reflected from the wind tunnel walls are responsible for the cases where there is poor periodicity and poor correlation with the predictions.

scholarly journals Wind Tunnel Wall Effects in a Linear Oscillating Cascade

1991 ◽  
Author(s):  
D. H. Buffum ◽  
S. Fleeter
Keyword(s):  
Wind Tunnel ◽  
Phase Angle ◽  
Detrimental Effect ◽  
Subsonic Flow ◽  
Poor Correlation ◽  
Tunnel Wall ◽  
Unsteady Aerodynamic ◽  
Unsteady Surface Pressure ◽  
Good For ◽  
Interblade Phase Angle

Experiments in a linear oscillating cascade reveal that the wind tunnel walls enclosing the airfoils have, in some cases, a detrimental effect on the oscillating cascade aerodynamics. In a subsonic flow field, biconvex airfoils are driven simultaneously in harmonic, torsion-mode oscillations for a range of interblade phase angle values. It is found that the cascade dynamic periodicity — the airfoil-to-airfoil variation in unsteady surface pressure — is good for some values of interblade phase angle but poor for others. Correlation of the unsteady pressure data with oscillating flat plate cascade predictions is generally good for conditions where the periodicity is good and poor where the periodicity is poor. Calculations based upon linearized unsteady aerodynamic theory indicate that pressure waves reflected from the wind tunnel walls are responsible for the cases where there is poor periodicity and poor correlation with the predictions.

scholarly journals Numerical Investigation of Unsteady Subsonic Compressible Flows Through an Oscillating Cascade

1986 ◽  
Author(s):  
T. H. Fransson ◽  
M. Pandolfi
Keyword(s):  
Phase Angle ◽  
Compressible Flows ◽  
Subsonic Flow ◽  
Aerodynamic Force ◽  
Plate Theory ◽  
Time Dependent ◽  
Periodicity Condition ◽  
Damping Coefficients ◽  
Flow Through ◽  
Interblade Phase Angle

A method for solving numerically the fully time-dependent two-dimensional Euler equations, applied to unsteady subsonic flow through vibrating turbomachine cascades with thin blades, is developed. The blades are assumed to vibrate at a constant interblade phase angle and the computed region is reduced to one blade passage, with the implementation of the interblade phase angle as a periodicity condition. The reliability of the method is validated by comparing it with an analytical flat plate theory, and the importance of radiative inlet and outlet boundary conditions for unsteady flow calculations is shown in an example. The method can be used to compute the aerodynamic force and damping coefficients acting on the blades and to investigate the propagation of unsteady disturbances through a cascade in flutter conditions.

Development and Validation of a CFD Technique for the Aerodynamic Analysis of HAWT

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
S. Gómez-Iradi ◽  
R. Steijl ◽  
G. N. Barakos
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Wind Tunnel Test ◽  
Unsteady Aerodynamics ◽  
Tunnel Wall ◽  
Local Flow ◽  
Flow Angle ◽  
Thrust And Torque

This paper demonstrates the potential of a compressible Navier–Stokes CFD method for the analysis of horizontal axis wind turbines. The method was first validated against experimental data of the NREL/NASA-Ames Phase VI (Hand, et al., 2001, “Unsteady Aerodynamics Experiment Phase, VI: Wind Tunnel Test Configurations and Available Data Campaigns,” NREL, Technical Report No. TP-500-29955) wind-tunnel campaign at 7 m/s, 10 m/s, and 20 m/s freestreams for a nonyawed isolated rotor. Comparisons are shown for the surface pressure distributions at several stations along the blades as well as for the integrated thrust and torque values. In addition, a comparison between measurements and CFD results is shown for the local flow angle at several stations ahead of the wind turbine blades. For attached and moderately stalled flow conditions the thrust and torque predictions are fair, though improvements in the stalled flow regime are necessary to avoid overprediction of torque. Subsequently, the wind-tunnel wall effects on the blade aerodynamics, as well as the blade/tower interaction, were investigated. The selected case corresponded to 7 m/s up-wind wind turbine at 0 deg of yaw angle and a rotational speed of 72 rpm. The obtained results suggest that the present method can cope well with the flows encountered around wind turbines providing useful results for their aerodynamic performance and revealing flow details near and off the blades and tower.

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.

Wind-tunnel wall effects on delta wings

1989 ◽  
Vol 26 (5) ◽  
pp. 403-404 ◽  
Author(s):  
Neal T. Frink
Keyword(s):  
Wind Tunnel ◽  
Wall Effects ◽  
Tunnel Wall ◽  
Delta Wings

scholarly journals Unsteady Gapwise Periodicity of Oscillating Cascaded Airfoils

1982 ◽  
Author(s):  
F. O. Carta
Keyword(s):  
Unsteady Flow ◽  
Fourier Coefficient ◽  
Phase Angle ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Pressure Data ◽  
Linear Cascade ◽  
Aerodynamic Damping ◽  
The Stability ◽  
Interblade Phase Angle

Tests were conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade and over the chord of the center blade. The pressure data were reduced to Fourier coefficient form for direct comparison, and were also processed to yield integrated loads and, particularly, the aerodynamic damping coefficient. In addition, results from two unsteady theories for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results that emerged from this investigation were: (a) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested, (b) as before, the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades, and (c) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.

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