Compressibility effects on oscillating rotor blades in hovering flight

Jones, W. P.; Rao, B. M.

doi:10.2514/3.5663

Cited by 11 publications

(2 citation statements)

References 5 publications

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“…The general integral is more difficult to evaluate, but if points along mid-chord only for which X\ = 0 are considered, we find that E(X,Y l ) -f: -I) 1 -I) 1 (50)…”

Section: Compressible Flowmentioning

confidence: 99%

Tip vortex effects on oscillating rotor blades in hovering flight

Jones

Rao

1971

AIAA Journal

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In rotor blade flutter studies, the airloads are usually estimated by the use of two-dimensional strip theory, and the effects of tip vortices and trailing vortices are generally neglected. The present paper examines the validity of this method of approach and gives results which reveal to what extent the assumptions made are acceptable. Compressibility and frequency effects are taken fully into account, but curvature effects resulting from the helical nature of the wake are ignored. The latter are assumed to be negligible when the frequency of oscillation of the blades is such that each blade of the rotor oscillates at several cycles per rotation. From the general theory developed, it is concluded that up to tip Mach numbers of about 0.8, the use of two-dimensional strip theory would not lead to serious error provided the blades oscillate at several cycles per rotation. This general conclusion is derived on the basis of a comparison of the downwash induced at points along the blade as given by the usual twodimensional theory and the corresponding values derived by an improved method which takes tip effects into account. In the more accurate theory, the two-dimensional mathematical model of the flow normally adopted is replaced by a modified version in which the trailing vortices are fully represented.

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“…The general integral is more difficult to evaluate, but if points along mid-chord only for which X\ = 0 are considered, we find that E(X,Y l ) -f: -I) 1 -I) 1 (50)…”

Section: Compressible Flowmentioning

confidence: 99%

Tip vortex effects on oscillating rotor blades in hovering flight

Jones

Rao

1971

AIAA Journal

Self Cite

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“…A rotating beam finite element in which the interpolating shape functions are obtained by satisfying the governing static homogenous differential equation of Euler-Bernoulli rotating beams is developed by Babu Gunda and Ganguli (2008). Loewy's 2-D unsteady aerodynamic theory (Loewy 1957), as amended by Hammond (1969), Jones and Rao (1970) provides a useful tool for examining blade flutter in hover. Additionally, Loewy showed how shed layers of vorticity affect Theodorsen's lift deficiency function (Theodorsen 1935), and influence the unsteady aerodynamic lift and moment equations.…”

Section: Introductionmentioning

confidence: 99%

Preparation of bi-polar membranes and their application to hypochlorite production

Kim¹,

Cho²,

Rhim³

et al. 2015

Membr. Water Treat.

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Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarterchord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

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Effect of phase angle on multibladed rotor flutter

Murthy

Pierce

1976

Journal of Sound and Vibration

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Compressibility effects on oscillating rotor blades in hovering flight

Cited by 11 publications

References 5 publications

Tip vortex effects on oscillating rotor blades in hovering flight

Tip vortex effects on oscillating rotor blades in hovering flight

Preparation of bi-polar membranes and their application to hypochlorite production

Effect of phase angle on multibladed rotor flutter

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