An Experimental Determination of the Unsteady Aerodynamics in a Controlled Oscillating Cascade

1977 ◽  
Vol 99 (1) ◽  
pp. 88-96 ◽  
Author(s):  
S. Fleeter ◽  
A. S. Novick ◽  
R. E. Riffel ◽  
J. E. Caruthers
Keyword(s):  
Phase Angle ◽  
Unsteady Aerodynamics ◽  
Time Dependent ◽  
Phase Lag ◽  
Reduced Frequency ◽  
On Line ◽  
Torsional Frequency ◽  
Airfoil Cascade ◽  
Interblade Phase Angle

A unique supersonic inlet flow field unsteady cascade experiment is described wherein the time-dependent pressure distribution within an harmonically oscillating airfoil cascade is quantitatively determined. The torsional frequency of oscillation and the inter-blade phase angle are precisely controlled by means of on-line digital computers. The dynamic data obtained include the chordwise distribution of the unsteady pressure magnitude and its phase lag as referenced to the airfoil motion. Parameters varied include the cascade inlet Mach number, the interblade phase angle, and the reduced frequency. The time-dependent data are correlated with state-of-the-art analytical predictions.

scholarly journals The Aerodynamics of an Oscillating Cascade in a Compressible Flow Field

1989 ◽  
Author(s):  
Daniel H. Buffum ◽  
Sanford Fleeter
Keyword(s):  
Phase Angle ◽  
Incidence Angle ◽  
Major Effect ◽  
Nasa Lewis Research ◽  
Airfoil Surface ◽  
Torsion Mode ◽  
Unique Data ◽  
Reduced Frequency ◽  
Airfoil Cascade ◽  
Interblade Phase Angle

Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of biconvex airfoils executing torsion mode oscillations at realistic reduced frequency values. Both steady and unsteady airfoil surface pressures are measured at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 degrees, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interblade phase angle values. The time-variant pressures are analyzed by means of discrete Fourier transform techniques, with these unique data compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle has a major effect on the chordwise distributions of the airfoil surface unsteady pressure, with the effects of reduced frequency, incidence angle, and Mach number somewhat less significant.

The Aerodynamics of an Oscillating Cascade in a Compressible Flow Field

1990 ◽  
Vol 112 (4) ◽  
pp. 759-767 ◽  
Author(s):  
D. H. Buffum ◽  
S. Fleeter
Keyword(s):  
Incidence Angle ◽  
Major Effect ◽  
Cascade Model ◽  
Nasa Lewis Research ◽  
Airfoil Surface ◽  
Torsion Mode ◽  
Unique Data ◽  
Reduced Frequency ◽  
Airfoil Cascade ◽  
Interblade Phase Angle

Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of bioconvex airfoils executing torsion mode oscillations at realistic reduced frequency values. Both steady and unsteady airfoil surface pressures are measured at two inlet Mach numbers, 0.65 and 0.80. and two incidence angles, 0 and 7 deg, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interbladephase angle values. The time-variant pressures are analyzed by means of discrete Fourier transform techniques, with these unique data compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle has a major effect on the chordwise distributions of the airfoil surface unsteady pressure, with the effects of reduced frequency, incidence angle, and Mach number somewhat less significant.

Effect of Shock Wave Movement on Aerodynamic Instability of Annular Cascade Oscillating in Transonic Flow

1988 ◽  
Author(s):  
Hiroshi Kobayashi
Keyword(s):  
Shock Wave ◽  
Phase Angle ◽  
Test Facility ◽  
Blade Surface ◽  
Compressor Cascade ◽  
Reduced Frequency ◽  
Wide Range ◽  
Cascade Flutter ◽  
Annular Cascade ◽  
Interblade Phase Angle

Effects attributable to shock wave movement on cascade flutter were examined for both turbine and compressor blade rows, using a controlled-oscillating annular cascade test facility and a method for accurately measuring time-variant pressures on blade surfaces. Nature of the effects and blade surface extent influenced by the shock movement were clarified in a wide range of Mach number, reduced frequency and interblade phase angle. Remarkable unsteady aerodynamic force was generated by the shock movement and it significantly affected the occurrence of compressor cascade flutter as well as turbine one. For turbine cascade the interblade phase angle remarkably controlled the effect of the force, while for compressor one the reduced frequency dominated it. The chordwise extent on blade surface influenced by the shock movement was suggested to be about 6% chord length.

Study of the aerodynamics of in-plane motion

2001 ◽  
Vol 215 (2) ◽  
pp. 89-104
Author(s):  
S T Shaw ◽  
N Qin
Keyword(s):  
Mach Number ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Transfer Operator ◽  
Unsteady Aerodynamics ◽  
Equation Model ◽  
Step Change ◽  
Phase Lag ◽  
Reduced Frequency ◽  
Advance Ratio

A computational analysis is performed of the unsteady aerodynamics associated with the blade sections of helicopter rotors in forward flight. The unsteady flow is studied through solutions of the two- dimensional Reynolds averaged Navier-Stokes equations together with a strongly coupled two-equation model of turbulence. Two motions are studied. The first motion is that of an aerofoil subjected to harmonic in-plane oscillations. The influence of advance ratio and reduced frequency is investigated. It is shown that, in the absence of shock waves, the flow is periodic with a reduced frequency equal to that of the forcing motion. However, the flow development lags behind the forcing motion. Furthermore, for constant reduced frequency the phase lag is independent of advance ratio. In addition to harmonic motion, the aerodynamic response to a step change in Mach number is investigated. Using an assumed form of the response of lift coefficient to a step change in Mach number, a lift transfer operator for step changes in Mach number is obtained in the Laplace domain. An analytical expression for the response to harmonic Mach number oscillations is then obtained from the transfer operator. The resulting formulation for the aerodynamic response confirms that the lag between the forcing motion and the aerodynamic response is independent of advance ratio.

Prediction of Aerodynamically Induced Vibrations in Turbomachinery Blading

1983 ◽  
Vol 105 (4) ◽  
pp. 375-381 ◽  
Author(s):  
D. Hoyniak ◽  
S. Fleeter
Keyword(s):  
Energy Balance ◽  
Incidence Angle ◽  
Forced Response ◽  
Aerodynamic Coefficients ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Balance Technique ◽  
Energy Dissipated ◽  
Airfoil Cascade ◽  
Interblade Phase Angle

To predict the aerodynamically forced response of an airfoil, an energy balance between the unsteady aerodynamic work and the energy dissipated through the airfoil structural and aerodynamic damping is performed. Theoretical zero incidence unsteady aerodynamic coefficients are then utilized in conjunction with this energy balance technique to predict the effects of reduced frequency, inlet Mach number, cascade geometry and interblade phase angle on the torsion mode aerodynamically forced response of the cascade. In addition, experimental unsteady aerodynamic gust data for flat plate and cambered cascaded airfoils are used together with these theoretical cascade unsteady self-induced aerodynamic coefficients to indicate the effects of incidence angle and airfoil camber on the forced response of the airfoil cascade.

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.

Effect of Adjacent Blade Motion on the Aerodynamics of a Linear Cascade Blade

2012 ◽  
Author(s):  
K. Naresh Babu ◽  
A. Kushari ◽  
C. Venkatesan
Keyword(s):  
Phase Angle ◽  
Unsteady Aerodynamics ◽  
Major Effect ◽  
Compressor Blades ◽  
Unsteady Forces ◽  
Linear Cascade ◽  
Reduced Frequency ◽  
The Stability ◽  
Lift And Drag ◽  
Phase Angles

Due to the trend of increasing power and reducing weight, the fan and compressor blades of turbo machinery might be more sensitive to flutter, which must strictly be avoided in the design process. In order to increase our understanding of the flutter phenomena for fan and compressor cascades, aero-elastic investigations are essential. In the present work experiments were performed in the specifically designed Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics forces and moments acting on a blade in a linear cascade of blades when the instrumented blade is stationary and the two adjacent blades on both sides of the instrumented blade are executing torsion-mode oscillations about their mid-chord. A 5-component strain gage balance was used to measure the unsteady aerodynamic forces on the model blade. The forces were measured for six inter-blade phase angles (i.e., the phase angle between the moving blade motions at a given frequency where the central blade is stationary) at low subsonic conditions, different reduced frequencies and different stagger. The time-variant forces were analyzed and variation of lift and drag coefficients for different inter-blade phase angles and reduced frequencies were plotted. The experimental results indicate that the inter-blade phase angle had a major effect on the variation of the unsteady forces and that reduced frequency had a somewhat less significant effect. Also in order to investigate the influence of the reduced frequency and inter-blade phase angles on the global stability of the cascade and its local contributions, experiments were performed for different reduced frequencies and phase angles. At the higher inter-blade phase angles (180°) the blade remains aerodynamically stable at 0° stagger, but the stability reduces at higher stagger angles. The blade is usually unstable when the interblade phase angle is 0°. At different flow conditions, some of the inter-blade phase angles appear to be aerodynamically unstable.

Effects of Shock Waves on Aerodynamic Instability of Annular Cascade Oscillation in a Transonic Flow

1989 ◽  
Vol 111 (3) ◽  
pp. 222-230 ◽  
Author(s):  
H. Kobayashi
Keyword(s):  
Shock Waves ◽  
Phase Angle ◽  
Blade Surface ◽  
Turbine Cascade ◽  
Compressor Cascade ◽  
Reduced Frequency ◽  
Aerodynamic Instability ◽  
Cascade Flutter ◽  
Annular Cascade ◽  
Interblade Phase Angle

The effects of shock waves on the aerodynamic instability of annular cascade oscillation were examined for rows of both turbine and compressor blades, using a controlled-oscillating annular cascade test facility and a method for accurately measuring time-variant pressures on blade surfaces. The nature of the effects and blade surface extent affected by shock waves were clarified over a wide range of Mach number, reduced frequency, and interblade phase angle. Significant unsteady aerodynamic forces were found generated by shock wave movement, which markedly affected the occurrence of compressor cascade flutter as well as turbine cascade flutter. For the turbine cascade, the interblade phase angle significantly controlled the effect of force, while for the compressor cascade the reduced frequency controlled it. The chordwise extent of blade surface affected by shock movement was estimated to be approximately 6 percent chord length.

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