Laminar-turbulent transition in an electromagnetically levitated droplet

Abstract

During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds number of 600.

Surface Tension and Viscosity of the Ni‐based Superalloy CMSX‐4 Measured by the Oscillating Drop Method in Parabolic Flight Experiments

“…A transition from a laminar to a turbulent flow regime as a function of the rf-heater field could be demonstrated. In related experiments Egry [25] et al and Hayers [26] et al could demonstrate that under laminar flow conditions realistic viscosity values in agreement with independently measured values could be obtained. Thus, it can be safely assumed that with the heater field turned off, the positioner field reduced, and with the time delay between the shut off of the heater field and the application of pulses for surface oscillation excitation, turbulent fluid flow is absent providing realistic values of the viscosity.…”

Studies on Decarburisation and Desiliconisation of Levitated Fe–C–Si Alloy Droplets

“…Berry et al 17) showed that the localized viscosity can change by a factor of 2 due to positioning field while the heating coils can alter by a factor of four causing considerable anisotropic distribution of flow. Hyers et al 18) later showed that flow inside the droplet can change from a laminar flow to viscous flow as the Reynold's number reaches 600 (this value is about 2 300 for water flowing in a pipe) and used tracers to demonstrate that "noncoherent chaotic motion signifying emergence of turbulence inside the drop" occurs due to EML. Since viscosity controls Reynold number to a considerable extent and since it was shown that the viscosity is nonuniform within the droplet, the flow also could be complex having laminar to turbulent characteristics within the droplet.…”

Physical Property Measurements of Liquid Metals at High Temperatures under Microgravity

“…In addition, the levitation field also induces fluid flow in the melt. 16) Therefore containerless techniques are only applicable to those problems where absence of convection is not mandatory. Thermophysical properties of levitated samples have been measured in microgravity during two Spacelab missions, using the electromagnetic levitation facility TEMPUS.…”