Showing papers on "Critical speed published in 1974"

An experimental study of Couette instability of stratified fluids

Abstract: The stability of Couette flow of stratified salt solutions is investigated in an apparatus with both the inner and outer cylinders rotating. The ratio of the radius of the inner cylinder to that of the outer cylinder is 0·2. The flow is visualized by means of shadowgraph and dye-trace methods. Compared with homogeneous fluids, the effect of the stabilizing density gradient is to increase the critical speed of the inner cylinder and to decrease the critical wavelength for a given angular speed of the outer cylinder. When the cylinders are rotating in the same direction, in the critical state, the instabilities appear along the inner cylinder in a spiral wave form which is itself not very stable. With counterrotating cylinders, the instabilities appear as regularly spaced vortices which, for the most part, are neither symmetric Taylor vortices nor simple spirals. In addition, these vortices rotate as a whole at a speed generally smaller than that of the inner cylinder. From shadowgraph observations, stability curves are constructed for three density gradients. The critical wavelength and the rotational periods of the vortices are also determined.

Bending-torsional flutter of a cantilevered wing containing a tip mass and subjected to a transverse follower force

Abstract: This paper is a study of the bending-torsional flutter of a cantilevered wing subjected to a follower force, and containing a lumped mass, at the free end In addition, a distributed aerodynamic loading is introduced along the wing This results in a set of nonself-adjoint differential equations with variable, complex coefficients whose solutions are obtainable only in series form Using the Frobenius method, a direct procedure is employed which retains the exact expression of the Theodorsen function and the unknown coefficients are evaluated on a computer which numerically converge to any prescribed accuracy It is found that, as a result of the interaction of the two sources of non-conservative loadings, the follower force reduces considerably the critical speed of flows in all cases studied An increase in the tip mass, however, has a stabilizing influence The effect of structural damping is also examined and it is shown that internal damping forces may have pronounced influences on the flutter speed of the system

Transient rotordynamic analysis for the space-shuttle main engine high-pressure oxygen turbopump

Abstract: A simulation study was conducted to examine the transient rotordynamics of the space shuttle main engine (SSME) high pressure oxygen turbopump (HPOTP) with the objective of identifying, anticipating, and avoiding rotordynamic problem areas. Simulations were performed for steady state operations at emergency power levels and for critical speed transitions. No problems are indicated in steady state operation of the HPOTP emergency power levels, although the results indicated that a rubbing condition will be experienced during critical speed transition at shutdown, particularly involving rotor deceleration rate and imbalance distribution rubbing at the turbine floating-ring seals. The condition is correctable by either reducing the imbalance at the HPOTP hot gas turbine wheels, or by a more rapid deceleration of the rotor through it critical speed.

On the Vibration of a Rotating Shaft System Having Two Rotors

Abstract: In this paper, the vibration and the critical speed of a rotating shaft having two rotors are treated theoretically considering the gyroscopic effect of the rotors and the distributed mass of the shaft. A symmetrical shaft system in which both rotors are symmetrical and an asymmetrical one in which rotors and the bending rigidity of the shaft are asymmetrical are treated using different coordinate systems respectively, and the eigen-frequencies at any shaft speed and the critical speeds are calculated exactly. An approximate formula for the lowest critical speed of a symmetrical rotating shaft system having n rotors by Rayleigh's method and one for critical speeds of higher order by Ritz's method are obtained considering the gyroscopic effect of the rotors, and numerical examples are shown.

Differential pressure sensing valve

Abstract: A control valve device especially adapted for the control of a marine engine so as to bypass a critical region of its speed range in which a resonant frequency vibration is encountered. The control valve comprises a differential piston abutment the stem of which cooperates with valve means to control the fluid pressure communication between either a first or second inlet and an outlet which controls the throttle of said engine. Detent means provides a latching force in either of two extreme positions to prevent actuation of the piston abutment in response to a variable speed control signal until the speed control signal reaches a value sufficient to overcome the latching force of the detent means, which latching force corresponds to the upper limit of the critical speed range. In one extreme position of the piston abutment, the valve means is effective to pressurize the outlet in accordance with the output of a regulating valve adjusted to limit the speed control signal to a value corresponding to the lower limit of the critical speed range, while in the other extreme position, the valve means is effective to pressurize the outlet in accordance with the speed control signal. The detent means may be employed either alone or in conjunction with a second regulating valve, the output of which biases the piston abutment in opposition to the speed control signal, to establish the upper limit of the critical speed range.