Mark J. Marr‐Lyon

Stabilization of a cylindrical capillary bridge far beyond the Rayleigh-Plateau limit using acoustic radiation pressure and active feedback

A novel method of suppressing the Rayleigh–Plateau capillary instability of a cylindrical liquid bridge is demonstrated which uses the radiation pressure of an ultrasonic wave to control the shape of the bridge. The shape of the bridge is optically sensed and the information used to control the spatial distribution of the radiation stress on the surface of the bridge. The feedback is phased so as to suppress the growth of the axisymmetric mode which normally becomes unstable when the slenderness, given by the length to diameter ratio, exceeds π. Stabilization is achieved out to a slenderness of 4.3 for a bridge density matched to the surrounding water bath in a Plateau tank. Breakup of such long bridges was found to produce a satellite drop from the receding thread of liquid. The active stabilization mechanism used may have application to other capillary systems.

Stabilization of electrically conducting capillary bridges using feedback control of radial electrostatic stresses and the shapes of extended bridges

Electrically conducting, cylindrical liquid bridges in a density-matched, electrically insulating bath were stabilized beyond the Rayleigh–Plateau (RP) limit using electrostatic stresses applied by concentric ring electrodes. A circular liquid cylinder of length L and radius R in real or simulated zero gravity becomes unstable when the slenderness S=L/2R exceeds π. The initial instability involves the growth of the so-called (2, 0) mode of the bridge in which one side becomes thin and the other side rotund. A mode-sensing optical system detects the growth of the (2, 0) mode and an analog feedback system applies the appropriate voltages to a pair of concentric ring electrodes positioned near the ends of the bridge in order to counter the growth of the (2, 0) mode and prevent breakup of the bridge. The conducting bridge is formed between metal disks which are grounded. Three feedback algorithms were tested and each found capable of stabilizing a bridge well beyond the RP limit. All three algorithms stabiliz...

Active electrostatic stabilization of liquid bridges in low gravity

In experiments performed aboard NASAs low-gravity KC-135 aircraft, it was found that rapid active control of radial electrostatic stresses can be used to suppress the growth of the (2,0) mode on capillary bridges in air. This mode naturally becomes unstable on a cylindrical bridge when the length exceeds the Rayleigh–Plateau (RP) limit. Capillary bridges having a small amount of electrical conductivity were deployed with a ring electrode concentric with each end of the bridge. A signal produced by optically sensing the shape of the bridge was used to control the electrode potentials so as to counteract the growth of the (2,0) mode. Occasionally the uncontrolled growth of the (3,0) mode was observed when the length far exceeded the RP limit. Rapid breakup from the growth of the (2,0) mode on long bridges was confirmed following deactivation of the control.

Radiation pressure of standing waves on liquid columns and small diffusion flames

The radiation pressure of standing ultrasonic waves in air is demonstrated in this investigation to influence the dynamics of liquid columns and small flames. With the appropriate choice of the acoustic amplitude and wavelength, the natural tendency of long columns to break because of surface tension was suppressed in reduced gravity [M. J. Marr‐Lyon, D. B. Thiessen, and P. L. Marston, Phys. Rev. Lett. 86, 2293–2296 (2001); 87(20), 9001(E) (2001)]. Evaluation of the radiation force shows that narrow liquid columns are attracted to velocity antinodes. The response of a small vertical diffusion flame to ultrasonic radiation pressure in a horizontal standing wave was observed in normal gravity. In agreement with our predictions of the distribution of ultrasonic radiation stress on the flame, the flame is attracted to a pressure antinode and becomes slightly elliptical with the major axis in the plane of the antinode. The radiation pressure distribution and the direction of the radiation force follow from the...

Active acoustic stabilization of capillary bridges significantly beyond the Rayleigh limit: Experimental confirmation.

Liquid bridges between two solid surfaces have applications in low gravity such as the solidification of floating zones. Long bridges naturally become unstable to a symmetric mode by bulging near one end while the opposite end thins. For a cylindrical bridge in low gravity of radius R and length L, the slenderness S=L/2R has a natural (Rayleigh) limit of π beyond which the bridge breaks. It has been demonstrated that acoustic radiation pressure may be used in simulated low gravity to produce stable bridges significantly beyond the Rayleigh limit with S as large as 3.6. The bridge (PDMS mixed with a dense liquid) has the same density as the surrounding water bath containing an ultrasonic standing wave. Modulation can be used to excite specific bridge modes [Morse et al., Phys. Fluids 8, 3–5 (1996)]. The shape of our bridge is optically sensed and the ultrasonic drive is electronically adjusted such that the radiation stress distribution dynamically quenches the most unstable mode. This active control simul...

Passive stabilization of capillary bridges in air with acoustic radiation pressure and the equilibrium shape of bridges

Long liquid cylinders ordinarily become unstable because of a capillary instability originally studied by Rayleigh and Plateau. In the present research liquid bridges in air were acoustically stabilized to 43% beyond the natural limiting length identified by Rayleigh and Plateau [Marr‐Lyon, Thiessen, and Marston, Phys. Rev. Lett. (to be published)]. The stabiliza‐tion was achieved by placing the bridge at the velocity antinode of a standing wave and selecting the wavelength such that the surface‐averaged radiation pressure of the sound field increases with increasing bridge radius. The tests were performed on NASA’s KC‐135 aircraft in weightless conditions on bridges having volumes equal to that of a circular cylinder of the same length as the bridge. In the standing wave, the bridge becomes elliptical because of the spatial distribution of the radiation pressure. Calculations of the scattering of sound by elliptical cylinders using Mathieu functions show that elliptical deformation only weakly affects th...

Passive and Active Stabilization of Liquid Bridges in Low Gravity

Tests are planned in the low gravity environment of the International Space Station (ISS) of new methods for the suppression of the capillary instability of liquid bridges. Our suppression methods are unusual in that they are not limited to liquid bridges having very special properties and may impact a variety of lowgravity and earth-based technologies. There are two main approaches to be investigated: (1) Passive Acoustic Stabilization (PAS) and (2) Active Electrostatic Stabilization (AES). In PAS, the suppression of the mode growth is accomplished by placing the bridge in an acoustic field having the appropriate properties such that the acoustic radiation pressure automatically pulls outward on the thinnest portion of the bridge. In AES, the bridge deformation is sensed optically and counteracted by actively adjusting the electrostatic Maxwell stresses via two ring electrodes concentric with the slightly conducting bridge to offset the growth of the unstable mode. While the present work emphasizes cylindrical bridges, the methods need not be restricted to that case. The methods to be explored are relevant to the suppression of capillary instabilities in floating zone crystal growth, breakup of liquid jets and columns, bubbles, and annular films as well as the management of coolants or propellants in low-gravity. Copyright

Active stabilization of liquid capillary bridges using optically sensed modal amplitudes

Cylindrical capillary bridges consisting of liquid between two circular supports naturally become unstable and break when the length of the bridge exceeds its circumference for the situation where the weight or buoyancy of the bridge can be neglected. This is the Rayleigh–Plateau (RP) slenderness limit which is relevant to the management of liquids and to the formation of liquid drops. We have demonstrated methods of suppressing this instability based on the optical sensing of the instantaneous modal amplitude and the rapid adjustment of the axial distribution of applied radial stress. This applied stress may be the result of ultrasonic radiation pressure [M. J. Marr‐Lyon et al., J. Fluid Mech. 351, 345–357 (1997)] or electrostatic stresses from an array of electrodes [M. J. Marr‐Lyon et al., Phys. Fluids (accepted)]. We have stabilized bridges as much as 42% beyond the RP limit by phasing the stress so that the effective modal spring constant becomes positive; however, the modal damping is then decreased...

Single‐bubble sonoluminescence in water during transitions from hypergravity to low gravity on NASA’s KC‐135 aircraft and laser‐beam extinction methods for studying bubble dynamics

The sound field which drives SBSL also provides the radiation force which counteracts the average buoyancy of the bubble. One consequence is that the location of the bubble should be altered by the effective acceleration of gravity ge. Variations in ge may alter the physical processes giving rise to luminescence. This group’s previous experiments have confirmed that SBSL is not automatically quenched in the reduced and enhanced ge conditions in an aircraft undergoing parabolic flight trajectories [D. B. Thiessen et al., in Proc. of the 4th Microgravity Fluid Phys. Conf. (NASA, 1998), pp. 379–383]. The new experiments were carried out with the SBSL chamber in contact with a constant‐pressure gas‐filled chamber. During intervals of negligible drift in the SBSL intensity, there can be a rapid intensity rise (with a relaxation time of about 5 s) of about 4% as ge is decreased from 1.8 to near 0 g, but the increase is not seen in all data sets. In related work, diagnostics based on monitoring laser‐beam extinc...

Probing and stabilization of interfaces with acoustic radiation pressure: Application to bubbles and capillary bridges

Acoustic radiation pressure at interfaces can be used as a probe of dynamics and as a method of suppressing instability. Examples include the probing of the interfacial rheology of acoustically levitated bubbles in water in the presence of surfactants which are either insoluble [T. J. Asaki, D. B. Thiessen, and P. L. Marston, Phys. Rev. Lett. 75, 2686–2689 and 4336 (1995)] or soluble [T. J. Asaki and P. L. Marston, J. Acoust. Soc. Am. 102, 3372–3377 (1997)] in water. Modulated radiation pressure was also used to probe the dynamics of liquid bridges of oil surrounded by water [S. F. Morse, D. B. Thiessen, and P. L. Marston, Phys. Fluids 8, 3–5 (1996)] and to suppress the breakup of cylindrical bridges having lengths significantly beyond the natural Rayleigh–Plateau limiting length [M. J. Marr‐Lyon, D. B. Thiessen, and P. L. Marston, J. Fluid Mech. 351, 345–357 (1997)]. In all of these examples the interfacial tension is significant for the normal modes of interest. Normal‐mode frequencies can be significan...