Unsteady Aerodynamic Response of a Two-Dimensional Airfoil at High Reduced Frequency

AIAA Journal ◽  
1974 ◽  
Vol 12 (1) ◽  
pp. 43-48 ◽  
Author(s):  
G. L. COMMERFORD ◽  
F. O. CARTA
Keyword(s):  
Two Dimensional ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency

On the Application of a Linearized Unsteady Potential-Flow Analysis to Fan-Tip Cascades

1986 ◽  
Vol 108 (1) ◽  
pp. 59-67
Author(s):  
W. J. Usab ◽  
J. M. Verdon
Keyword(s):  
Potential Flow ◽  
Vibrational Frequency ◽  
Numerical Solutions ◽  
Flow Analysis ◽  
Experimental Measurements ◽  
Two Dimensional ◽  
Good Qualitative Agreement ◽  
Blade Loading ◽  
Unsteady Aerodynamic ◽  
Flow Phenomena

A linearized potential flow analysis, which accounts for the effects of nonuniform steady flow phenomena on the unsteady response to prescribed blade motions, has been applied to five two-dimensional cascade configurations. These include a flat-plate cascade and three cascades which are representative of the tip sections of current fan designs. Here the blades are closely spaced, highly staggered, and operate at low mean incidence. The fifth configuration is a NASA Lewis cascade of symmetric biconvex airfoils for which experimental measurements are available. Numerical solutions are presented that clearly illustrate the effects and importance of blade geometry and mean blade loading on the linearized unsteady response at high subsonic inlet Mach number and high blade-vibrational frequency. In addition, a good qualitative agreement is shown between the analytical predictions and experimental measurements for the cascade of symmetric biconvex airfoils. Finally, recommendations on the research needed to extend the range of application of linearized unsteady aerodynamic analyses are provided.

scholarly journals Scaling the propulsive performance of heaving and pitching foils

2017 ◽  
Vol 822 ◽  
pp. 386-397 ◽  
Author(s):  
Daniel Floryan ◽  
Tyler Van Buren ◽  
Clarence W. Rowley ◽  
Alexander J. Smits
Keyword(s):  
Strouhal Number ◽  
Linear Dependence ◽  
Scaling Laws ◽  
Biological Data ◽  
Viscous Drag ◽  
Water Tunnel ◽  
Two Dimensional ◽  
Propulsive Performance ◽  
Reduced Frequency ◽  
Two Dimensional Flow

Scaling laws for the propulsive performance of rigid foils undergoing oscillatory heaving and pitching motions are presented. Water tunnel experiments on a nominally two-dimensional flow validate the scaling laws, with the scaled data for thrust, power and efficiency all showing excellent collapse. The analysis indicates that the behaviour of the foils depends on both Strouhal number and reduced frequency, but for motions where the viscous drag is small the thrust closely follows a linear dependence on reduced frequency. The scaling laws are also shown to be consistent with biological data on swimming aquatic animals.

Comparison of the Unsteady Loads of an Airfoil in the Pitching and Plunging Motions

2006 ◽  
Author(s):  
M. Soltani ◽  
M. Seddighi ◽  
F. Rasi
Keyword(s):  
Subsonic Flow ◽  
Free Stream ◽  
Incident Angle ◽  
Oscillation Amplitude ◽  
Stream Velocity ◽  
Frequency Oscillation ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Series Of Experiments

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of motion on the unsteady aerodynamic loads of the airfoil at pre-stall, near stall, and post stall conditions. Variations of the aerodynamic coefficients with equivalent angle of attack for both pitching and plunging motions showed strong sensitivity to the reduced frequency, oscillation amplitude, Reynolds number, and mean angles of attack.

Annular Cascade Study of Low Back-Pressure Supersonic Fan Blade Flutter

1990 ◽  
Vol 112 (4) ◽  
pp. 768-777 ◽  
Author(s):  
H. Kobayashi
Keyword(s):  
Back Pressure ◽  
Low Back ◽  
Aerodynamic Forces ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Blade Flutter ◽  
Fan Blade ◽  
Cascade Flutter ◽  
Annular Cascade ◽  
Phase Angles

Low back-pressure supersonic fan blade flutter in the torsional mode was examined using a controlled-oscillating annular cascade test facility. Precise data of unsteady aerodynamic forces generated by shock wave movement, due to blade oscillation, and the previously measured data of chordwise distributions of unsteady aerodynamic forces acting on an oscillating blade, were joined and, then, the nature of cascade flutter was evaluated. These unsteady aerodynamic forces were measured by direct and indirect pressure measuring methods. Our experiments covered a range of reduced frequencies based on a semichord from 0.0375 to 0.547, six interblade phase angles, and inlet flow velocities from subsonic to supersonic flow. The occurrence of unstalled cascade flutter in relation to reduced frequency, interblade phase angle, and inlet flow velocity was clarified, including the role of unsteady aerodynamic blade surface forces on flutter. Reduced frequency of the flutter boundary increased greatly when the blade suction surface flow became transonic flow. Interblade phase angles that caused flutter were in the range from 40 to 160 deg for flow fields ranging from high subsonic to supersonic. Shock wave movement due to blade oscillation generated markedly large unsteady aerodynamic forces which stimulated blade oscillation.

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