Amplitude Of Fluid Oscillation Research Articles

Magnetic damping of steady streaming vortices in an oscillatory viscous flow over a wavy wall

The effect of a transverse magnetic field on the steady streaming vortices generated by an oscillatory viscous flow over a wavy wall is studied. The wall is assumed to be electrically insulated, and the axial magnetic field induced by the electric currents circulating in the fluid is neglected. A perturbative solution is developed assuming that the amplitude of fluid oscillation is very small compared with the wall wavelength and that the amplitude of the wavy wall is much smaller than the Stokes layer. Upper and lower steady regions of recirculation appear when the wavelength of the wall is much larger than the Stokes layer thickness. This steady streaming flow is found to be damped out by the action of the magnetic field. As the magnetic field strength increases, momentum diffuses out along the field lines causing the elongation of the vortices in the field direction. As a consequence of the flow two-dimensionality, the streaming vortices can be completely annihilated by magnetic braking. This behavior is confirmed through numerical calculations. In the absence of a magnetic field, a correction to the Rayleigh’s law of streaming is obtained.

Steady streaming from a noncompact sphere

An analytical study has been conducted of acoustic streaming around a rigid sphere in a plane standing acoustic field under the noncompact sphere approximation. Under these conditions the sphere size is allowed to be comparable to the (radian) wavelength of the acoustic field, thus making the usually ignored compressibility effects significant in the flow. However, the amplitude of fluid oscillations is assumed small compared to the sphere size, and their ratio serves as the appropriate perturbation parameter in the matched asymptotic technique being used. The solution calls for a Helmholtz type decomposition of the velocity field into the sum of the gradient of a potential function, and the curl of a suitably vectorized stream function. The role of the nonlinear interactions of both the potential function and the stream function is pointed out, and the resulting streaming flow patterns are contrasted with those obtained in the incompressible case. This work would find application in determining transport rates in containerless processing using acoustic levitation with ultrasonic frequencies. [Work supported by NASA.]

Mass transfer enhancement in a symmetric sinusoidal wavy-walled channel for pulsatile flow

Mass transfer characteristics in a sinusoidal wavy-walled channel are investigated experimentally for pulsatile flow with varying flow parameters, i.e. net flow, amplitude and frequency of fluid oscillation. We show that combination of flow separation and fluid oscillation leads to a significant enhancement in the mass transfer rate under laminar flow conditions. This enhancement is due to rapid fluid mixing induced by the dynamic behavior of the vortex in this channel. The Sherwood number for pulsatile flow can be expressed by the following relation: Sh p m = Sh s m + Sh o m where m is the exponent, and subscripts mean s—steady flow, o—oscillatory flow and p—pulsatile flow. Although the value of m depends on the amplitude of fluid oscillation, it becomes constant at large amplitude, i.e. m = 4.

Non-linear viscous oscillatory flow over a small amplitude wavy wall

The non-linear viscous oscillatory flow over a wavy wall of small amplitude ∊∗ is determined. The solution holds for arbitrary values of a ∗/L ∗ (a ∗ is the amplitude of fluid oscillations near the wall and L ∗ is the wavelength of wall perturbation); previous works of Lyne [1], Kaneko and Honji [2] on the subject are thus extended. An independent analysis for small values of a ∗/L ∗ is performed and the results of the two approaches have been successfully compared. The form of the steady streamings set up in addition to the oscillatory motion by the bed profile is analyzed for different values of the parameters of the problem. The relevance of the results to the study of ripples formation at the bottom of sea waves is discussed.

Pressure and Fluid Oscillations in Vent System due to Steam Condensation, (I)

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional ...

Pressure and fluid oscillations in vent system due to steam condensation. I. Experimental results and analysis model for chugging.

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional motion of water column in and out of vent tubes. As the result, the characteristics of chugging phenomenon got in the experiment coulbd well be simulated. Chugging phenomenon, accompanying back flow of water into vent tubes, is a kind of low-frequency oscillation which is predominant in the pressure oscillation in the header.