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.

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.

Unsteady Aerodynamic Forces on Vibrating Annular Cascade Blades: Cross-Validation of the Linear Unsteady CFD Calculations Using the TVD Scheme and the Double Linearization Theory

2002 ◽  
Author(s):  
Nobuhiko Yamasaki ◽  
Masaaki Hamabe ◽  
Masanobu Namba
Keyword(s):  
Numerical Calculation ◽  
Delta Function ◽  
Point Of View ◽  
Tvd Scheme ◽  
Aerodynamic Forces ◽  
Unsteady Aerodynamic ◽  
Precise Calculation ◽  
Computational Resources ◽  
Volume Method ◽  
Annular Cascade

The paper presents the formulation to compute numerically the unsteady aerodynamic forces on the vibrating annular cascade blades. The formulation is based on the finite volume method, the type, and the TVD scheme, following the UPACS code developed by NAL, Japan. By applying the TVD scheme to the linear unsteady calculations, the precise calculation of the peak of unsteady aerodynamic forces at the shock wave location like the delta function singularity becomes possible without empirical constants. As a further feature of the present paper, results of the present numerical calculation are compared with those of the double linearization theory (DLT), which assumes small unsteady and steady disturbances but the unsteady disturbances are much smaller than the steady disturbances. Since DLT requires far less computational resources than the present numerical calculation, the validation of DLT is quite important from the engineering point of view. Under the conditions of small steady disturbances, a good agreement between these two results is observed, so that the two codes are cross-validated. The comparison also reveals the limitation on the applicability of DLT.

Linear unsteady aerodynamic forces on vibrating annular cascade blades

2003 ◽  
Vol 12 (2) ◽  
pp. 138-143 ◽  
Author(s):  
Taketo Nagasaki ◽  
Nobuhiko Yamasaki
Keyword(s):  
Aerodynamic Forces ◽  
Unsteady Aerodynamic ◽  
Annular Cascade

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.

Holographic Measurements and Theoretical Predictions of the Unsteady Flow in a Transonic Annular Cascade

1985 ◽  
Vol 107 (2) ◽  
pp. 450-457 ◽  
Author(s):  
M. R. D. Davies ◽  
P. J. Bryanston-Cross
Keyword(s):  
Finite Element ◽  
Frequency Parameter ◽  
Pressure Measurements ◽  
Blade Loading ◽  
Finite Element Calculations ◽  
Theoretical Predictions ◽  
Fan Blade ◽  
Blade Frequency ◽  
Annular Cascade ◽  
Phase Angles

A series of measurements have been made on a transonic annular cascade. The cascade which represents the tip section of a compressor fan blade has an inlet Mach number of 1.18. By the use of external vibrators it is possible to vibrate the blades independently in torsion simulating different interblade phase angles in order to gain an understanding of shock movement and blade loading. The results presented are made over interblade phase angles of 180 and 135 deg at a blade frequency parameter of 0.1, based on chord. The holographic data obtained shows detail of shock movement during the cycle using a miniature holocamera located within the hub of the cascade. Unsteady sidewall pressure measurements have also been obtained over the vibration cycle. The data obtained have been compared with finite element calculations.

Flutter of Swept Fan Blades

1985 ◽  
Vol 107 (2) ◽  
pp. 394-398
Author(s):  
R. E. Kielb ◽  
K. R. V. Kaza
Keyword(s):  
Detrimental Effect ◽  
Structural Model ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Aeroelastic Analysis ◽  
Flutter Analysis ◽  
Blade Flutter ◽  
Fan Blade ◽  
Element Technique ◽  
Nonuniform Beam

The purpose of the research presented in this paper is to study the effect of sweep on fan blade flutter by applying the analytical methods developed for aeroelastic analysis of advanced turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods, the unsteady aerodynamic loads are calculated using two-dimensional cascade theories that are modified to account for sweep. An advanced fan stage is analyzed with 0, 15, and 30 deg of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 deg of sweep.

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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