Biomedical subjects

W D McCormick

Publications and source records attributed to W D McCormick.

3 recordsLinked to original sources

PubMed2002

Fluctuations in viscous fingering.

Our experiments on viscous (Saffman-Taylor) fingering in Hele-Shaw channels reveal finger width fluctuations that were not observed in previous experiments, which had lower aspect ratios and higher capillary numbers Ca. These fluctuations intermittently narrow the finger from its expected width. The magnitude of these fluctuations is described by a power law, Ca(-0.64), which holds for all aspect ratios studied up to the onset of tip instabilities. Further, for large aspect ratios, the mean finger width exhibits a maximum as Ca is decreased instead of the predicted monotonic increase.

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PubMed2001

Suppression of dripping from a ceiling.

An isothermal layer suspended from a surface is gravitationally (Rayleigh-Taylor) unstable. We find that, when a vertical temperature difference DeltaT above a critical value (DeltaT)(c) is imposed across the liquid-gas layer system (heated from below), the restoring force provided by the temperature-dependent surface tension (thermocapillarity) can stabilize the layer. Our measurements of the most unstable wave number for DeltaT<(DeltaT)(c) agree well with our linear stability analysis. The instability occurs at long wavelengths: the most unstable wavelength at (DeltaT)(c) is infinite.

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PubMed1999

Instability of the Kolmogorov flow in a soap film.

We examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number R(c) is approximately equal to the square root of 2. In our soap film experiment, we find a critical value R(c) is approximately equal to 70. This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. Our observations indicate that flow in the soap film cannot be decoupled from flow in the surrounding gas.

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