Tait–Kirchhoff method for determining rotary and unsteady force derivatives

2014 ◽  
Vol 39 ◽  
pp. 384-394 ◽  
Author(s):  
Nicola de Divitiis
Keyword(s):  
Unsteady Force ◽  
Kirchhoff Method

On the unsteady inviscid force on cylinders and spheres in subcritical compressible flow

2008 ◽  
Vol 366 (1873) ◽  
pp. 2161-2175 ◽  
Author(s):  
M Parmar ◽  
A Haselbacher ◽  
S Balachandar
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Propagation Speed ◽  
Added Mass ◽  
The Body ◽  
Mass Force ◽  
Unsteady Force ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
Cylinders And Spheres

The unsteady inviscid force on cylinders and spheres in subcritical compressible flow is investigated. In the limit of incompressible flow, the unsteady inviscid force on a cylinder or sphere is the so-called added-mass force that is proportional to the product of the mass displaced by the body and the instantaneous acceleration. In compressible flow, the finite acoustic propagation speed means that the unsteady inviscid force arising from an instantaneously applied constant acceleration develops gradually and reaches steady values only for non-dimensional times c ∞ t / R ≳10, where c ∞ is the freestream speed of sound and R is the radius of the cylinder or sphere. In this limit, an effective added-mass coefficient may be defined. The main conclusion of our study is that the freestream Mach number has a pronounced effect on both the peak value of the unsteady force and the effective added-mass coefficient. At a freestream Mach number of 0.5, the effective added-mass coefficient is about twice as large as the incompressible value for the sphere. Coupled with an impulsive acceleration, the unsteady inviscid force in compressible flow can be more than four times larger than that predicted from incompressible theory. Furthermore, the effect of the ratio of specific heats on the unsteady force becomes more pronounced as the Mach number increases.

Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Fanny M. Besem ◽  
Joshua D. Kamrass ◽  
Jeffrey P. Thomas ◽  
Deman Tang ◽  
Robert E. Kielb
Keyword(s):  
Secondary Flows ◽  
Common Source ◽  
Structural Failure ◽  
Vortex Induced Vibration ◽  
Fluid Instability ◽  
Unsteady Force ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency ◽  
Lock In ◽  
High Angles Of Attack

Vortex-induced vibration is a fluid instability where vortices due to secondary flows exert a periodic unsteady force on the elastic structure. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These vibrations may cause material fatigue and are a common source of structural failure. This work uses a frequency domain, harmonic balance (HB) computational fluid dynamics (CFD) code to predict the natural shedding frequency and lock-in region of an airfoil at very high angles of attack. The numerical results are then successfully compared to experimental data from wind tunnel testings.

Refraction corrections for the Kirchhoff method

1997 ◽  
Author(s):  
Anthony Pilon ◽  
Anastasios Lyrintzis ◽  
Anthony Pilon ◽  
Anastasios Lyrintzis
Keyword(s):  
Kirchhoff Method

scholarly journals The Rotordynamic Forces on a Centrifugal Pump Impeller in the Presence of Cavitation

1990 ◽  
Vol 112 (3) ◽  
pp. 264-271 ◽  
Author(s):  
R. Franz ◽  
A. J. Acosta ◽  
C. E. Brennen ◽  
T. K. Caughey
Keyword(s):  
Full Range ◽  
Radial Force ◽  
Centrifugal Impeller ◽  
Dynamic Force ◽  
Pump Impeller ◽  
Unsteady Force ◽  
Fixed Radius ◽  
Eccentric Motion ◽  
Rotordynamic Forces ◽  
Rotor Dynamic

An experiment in forced vibration was conducted to study the fluid-induced rotor-dynamic force on an impeller whirling along a trajectory eccentric to its undeflected position in the presence of cavitation. The prescribed whirl trajectory of the rotor is a circular orbit of a fixed radius. The force measured is a combination of a steady radial force due to volute asymmetries and an unsteady force due to the eccentric motion of the rotor. These measurements have been conducted over a full range of whirl/impeller speed ratios at different flow coefficients without cavitation for various turbomachines. A destabilizing force was observed over a region of positive whirl ratio. The range of flow conditions examined for a centrifugal impeller in a spiral volute has been enlarged to include cavitation. Compared to the non-cavitating condition, cavitation corresponding to a head a loss of three percent did not have a significant effect upon the unsteady force. However, a lesser degree of cavitation at the design point increased the destabilizing force for a particular set of whirl ratios.

Ray‐Kirchhoff migration in inhomogeneous media

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 760-768 ◽  
Author(s):  
Tianfei Zhu
Keyword(s):  
Ray Tracing ◽  
Asymptotic Series ◽  
Inhomogeneous Media ◽  
Perturbation Scheme ◽  
Kirchhoff Migration ◽  
Reference Velocity ◽  
Higher Order Terms ◽  
Vertical Variations ◽  
Kirchhoff Method ◽  
Lateral Variations

A Kirchhoff method that avoids possible singularities on the surface of integration and is more accurate than previous Kirchhoff methods has been developed for seismic migration in laterally inhomogeneous media. It is based on a newly derived integral solution to the acoustic wave equation. This solution indicates that wave fields in an inhomogeneous medium can be expressed as a summation of ray solutions determined by the transport and extended eikonal equations. The extended eikonal equation is, in turn, solved by an asymptotic series. For implementation, a perturbation scheme is developed for solving the ray and transport equations. In addition to computing higher‐order terms of the asymptotic series, this scheme can be used to avoid most of the ray tracing required for wave extrapolation in a medium where vertical variations may be large but lateral variations are small compared to velocity itself. Where an analytic ray solution for the reference velocity used in the perturbation scheme exists, ray‐Kirchhoff migration in such a medium can be carried out without numerical ray tracing.

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