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.

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.

Unsteady Aerodynamic Damping Measurement of Annular Turbine Cascade With High Deflection in Transonic Flow

1990 ◽  
Vol 112 (4) ◽  
pp. 732-740 ◽  
Author(s):  
H. Kobayashi
Keyword(s):  
High Speed ◽  
Test Facility ◽  
Turbine Cascade ◽  
Torsional Mode ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Cascade Flutter ◽  
The Moment ◽  
Annular Cascade ◽  
Transonic Cascade

Unsteady aerodynamic forces acting on oscillating blades of a transonic annular turbine cascade were investigated in both aerodynamic stable and unstable domains, using a Freon gas annular cascade test facility. In the facility, whole blades composing the cascade were oscillated in the torsional mode by a high-speed mechanical drive system. In the experiment, the reduced frequency K was changed from 0.056 to 0.915 with a range of outlet Mach number M2 from 0.68 to 1.39, and at a constant interblade phase angle. Unsteady aerodynamic moments obtained by two measuring methods agreed well. Through the moment data the phenomenon of unstalled transonic cascade flutter was clarified as well as the significance of K and M2 for the flutter. The variation of flutter occurrence with outlet flow velocity in the experiments showed a very good agreement with theoretical analysis.

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.

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

1989 ◽  
Author(s):  
Hiroshi 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 semi-chord from 0.0375 to 0.547, 6 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 which caused flutter were in the range from 40° to 160° 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.

Experimental Study of Aerodynamic Damping of an Annular Compressor Cascade With Large Mean Incidences

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
M. C. Keerthi ◽  
Abhijit Kushari
Keyword(s):  
Torsional Oscillation ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Aerodynamic Damping ◽  
Reduced Frequency ◽  
Incidence Studies ◽  
Stable Performance ◽  
Phase Variations ◽  
The Stability ◽  
Interblade Phase Angle

This study addresses flutter that can occur in compressors when operating at high relative incidence. Studies are performed on a subsonic annular compressor cascade containing a sector of blades that can be subjected to controlled torsional oscillation. Measurements taken on the centrally located blade are used to study the unsteady surface pressures developed. Three large mean incidences are considered to characterize the aeroelastic performance. Aerodynamic damping is calculated for each test condition and its variation due to interblade phase angle (IBPA), reduced frequency, and incidence is studied. The source of stability or instability is traced to the nature of unsteady pressures. When the incidence is below the static-stall limit, an increasing incidence is found to exhibit aeroelastically more stable performance, whereas beyond the limit, the stability worsens. For the latter, the amount of improvement in stability by increasing reduced frequency is less compared to the former and its variation with IBPA is not as regular owing to the associated large uncertainty. The nonlinearity effects were found to be relatively higher for this case, especially from the aft region of the suction surface. It is also found that the phase of the local fluctuating pressure and its location on the chord has a decisive influence on the aerodynamic damping and its trends with respect to various parameters are discussed. The results are expected to be useful in the assessing aerodynamic damping trends in relation to the pressure phase variations in specific regions along the chord.

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.

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