Drag coefficient of a liquid domain in a two-dimensional membrane

Using a hydrodynamic theory that incorporates a momentum decay mechanism, we calculate the drag coefficient of a circular liquid domain of finite viscosity moving in a two-dimensional membrane. We derive an analytical expression for the drag coefficient which covers the whole range of domain sizes. Several limiting expressions are discussed. The obtained drag coefficient decreases as the domain viscosity becomes smaller with respect to the outer membrane viscosity. This is because the flow induced in the domain acts to transport the fluid in the surrounding matrix more efficiently.Comment: 8 pages, 5 Figures. Accepted for publication in Eur. Phys. J.

Turbulent drag on a low-frequency vibrating grid in superfluid He-4 at very low temperatures

We present measurements of the dissipative turbulent drag on a vibrating grid in superfluid He-4 over a wide range of (low) frequencies. At high velocities, the dissipative drag is independent of frequency and is approximately the same as that measured in normal liquid He-4. We present measurements on a similar grid in superfluid He-3-B at low temperatures which shows an almost identical turbulent drag coefficient at low frequencies. However, the turbulent drag in He-3-B is substantially higher at higher frequencies. We also present measurements of the inertial drag coefficient for grid turbulence in He-4. The inertial drag coefficient is significantly reduced by turbulence in both superfluid and normal liquid He-4

Orbital evolution under the action of fast interstellar gas flow with non-constant drag coefficient

The acceleration of a spherical dust particle caused by an interstellar gas flow depends on the drag coefficient which is, for the given particle and flow of interstellar gas, a specific function of the relative speed of the dust particle with respect to the interstellar gas. We investigate the motion of a dust particle in the case when the acceleration caused by the interstellar gas flow represent a small perturbation to the gravity of a central star. We present the secular time derivatives of the Keplerian orbital elements of the dust particle under the action of the acceleration from the interstellar gas flow for arbitrary orbit orientation. The semimajor axis of the dust particle is a decreasing function of time for an interstellar gas flow acceleration with constant drag coefficient and also for such an acceleration with the linearly variable drag coefficient. The decrease of the semimajor axis is slower for the interstellar gas flow acceleration with the variable drag coefficient. The minimal and maximal values of the decrease of the semimajor axis are determined. In the planar case, when the interstellar gas flow velocity lies in the orbital plane of the particle, the orbit always approaches the position with the maximal value of the transversal component of the interstellar gas flow velocity vector measured at perihelion. The properties of the orbital evolution derived from the secular time derivatives are consistent with numerical integrations of the equation of motion. If the interstellar gas flow speed is much larger than the speed of the dust particle, then the linear approximation of dependence of the drag coefficient on the relative speed of the dust particle with respect to the interstellar gas is usable for practically arbitrary (no close to zero) values of the molecular speed ratios (Mach numbers).Comment: 12 pages, 6 figures, 2 equations added in v

Determination of the hypersonic-continuum/rarefied-flow drag coefficient of the Viking lander capsule 1 aeroshell from flight data

Results of an investigation to determine the full scale drag coefficient in the high speed, low density regime of the Viking lander capsule 1 entry vehicle are presented. The principal flight data used in the study were from onboard pressure, mass spectrometer, and accelerometer instrumentation. The hypersonic continuum flow drag coefficient was unambiguously obtained from pressure and accelerometer data; the free molecule flow drag coefficient was indirectly estimated from accelerometer and mass spectrometer data; the slip flow drag coefficient variation was obtained from an appropriate scaling of existing experimental sphere data. Comparison of the flight derived drag hypersonic continuum flow regime except for Reynolds numbers from 1000 to 100,000, for which an unaccountable difference between flight and ground test data of about 8% existed. The flight derived drag coefficients in the free molecule flow regime were considerably larger than those previously calculated with classical theory. The general character of the previously determined temperature profile was not changed appreciably by the results of this investigation; however, a slightly more symmetrical temperature variation at the highest altitudes was obtained

An assessment of sphere drag coefficient data

Wind tunnel test data for falling sphere drag coefficient determinatio

A comparative study of immersed-boundary interpolation methods for a flow around a stationary cylinder at low Reynolds number

The accuracy and computational efficiency of various interpolation methods for the implementation of non grid-confirming boundaries is assessed. The aim of the research is to select an interpolation method that is both efficient and sufficiently accurate to be used in the simulation of vortex induced vibration of the flow around a deformable cylinder. Results are presented of an immersed boundary implementation in which the velocities near nonconfirming boundaries were interpolated in the normal direction to the walls. The flow field is solved on a Cartesian grid using a finite volume method with a staggered variable arrangement. The Strouhal number and Drag coefficient for various cases are reported. The results show a good agreement with the literature. Also, the drag coefficient and Strouhal number results for five different interpolation methods were compared it was shown that for a stationary cylinder at low Reynolds number, the interpolation method could affect the drag coefficient by a maximum 2% and the Strouhal number by maximum of 3%. In addition, the bi-liner interpolation method took about 2% more computational time per vortex shedding cycle in companion to the other methods

Modification to the shading routine in the HREC orbital drag coefficient computer program Final report

Shading and pre-shading techniques for modified orbital drag coefficient computer progra

Behavior of Spherical Particles at Low Reynolds Numbers in a Fluctuating Translational Flow. Preliminary Experiments

The behavior of small spheres in non-steady translational flow has been studied experimentally' for values of Reynolds nunber from 0 to 3000. The aim of the work was to improve our quantitative understanding of particle transport in turbulent gaseous media, a process of extreme importance in powerplants and energy transfer mechanisms. Particles, subjected to strong sinusoidal oscillations parallel to the direction of steady translation, were found to have changes in average drag coefficient depending upon their translational Reynolds number, the frequency and amplitude of the oscillations. When the Reynolds number based on the sphere diameter was les s than 200, the synunetric translational oscillation had negligible effect on the aver age particle dr ago For Reynolds numbers exceeding 300, the effective drag coefficient was significantly increased in a particular frequency range. For example, an increase in drag coefficient of 25 per cent was observed at a Reynolds nwnber of 3000 when the amplitude of the oscillation was 2 per cent of the sphere diazneter and the disturbance frequency was approximately the Strouhal frequency. The occurrence of the maximum effect at frequencies between one and two times the Stroubal frequency strongly suggests non-linear interaction between wake vortex shedding and the oscillation in translational motions. Flow visualization studies support this suggestion