arXiv subjects

Haitao Xu

Publications and source records attributed to Haitao Xu.

59 records · Page 4Linked to original sources

arXiv2008

Fluid Acceleration in the Bulk Turbulence of Dilute Polymer Solutions

We report experimental measurements of Lagrangian accelerations in the bulk of intense turbulent flows of dilute polymer solutions by following tracer particles with a high-speed optical tracking system. We observed a significant decrease in the acceleration variance in dilute polymer solutions. The shape of the normalized acceleration probability density functions, however, remain the same as in Newtonian water flows. We also observed an increase in the turbulent Lagrangian acceleration autocorrelation time in these dilute polymer solutions.

physics.flu-dyn↗

arXiv2007

Modification of the turbulent energy cascade by polymer additives

By tracking small particles in the bulk of an intensely turbulent flow, we show that even a very small concentration of long-chain polymers disrupts the usual turbulent energy cascade. The polymers affect scales much larger than their physical size, from the dissipation range to the inertial range. The effect depends strongly on the polymer concentration. While the dissipative-scale statistics change continuously as the polymer concentration is increased, the inertial-range energy transfer rate is only altered by the polymer additives when the concentration is above a threshold (approximately 5 parts per million by weight for the polymer we used).

physics.flu-dyn↗

arXiv2007

Evolution of geometric structures in intense turbulence

We report measurements of the evolution of lines, planes, and volumes in an intensely turbulent laboratory flow using high-speed particle tracking. We find that the classical characteristic time scale of an eddy at the initial scale of the object considered is the natural time scale for the subsequent evolution. The initial separation may only be neglected if this time scale is much smaller than the largest turbulence time scale, implying extremely high turbulence levels.

physics.flu-dyn↗

arXiv2007

Experimental measurement of acceleration correlations and pressure structure functions in high Reynolds number turbulence

We present measurements of fluid particle accelerations in turbulent water flows between counter-rotating disks using three-dimensional Lagrangian particle tracking. By simultaneously following multiple particles with sub-Kolmogorov-time-scale temporal resolution, we measured the spatial correlation of fluid particle acceleration at Taylor microscale Reynolds numbers between 200 and 690. We also obtained indirect, non-intrusive measurements of the Eulerian pressure structure functions by integrating the acceleration correlations. Our experimental data provide strong support to the theoretical predictions of the acceleration correlations and the pressure structure function in isotropic high Reynolds number turbulence by Obukhov and Yaglom in 1951. The measured pressure structure functions display K41 scaling in the inertial range.

physics.flu-dyn↗

arXiv2005

Pair Dispersion in Turbulence

Turbulent mixing of liquids and gasses is ubiquitous in nature. It is the basis of all industrial fluid mixing processes, and it determines the spread of pollutants or bioagents in the atmosphere and oceans. Biological organisms even use it to survive in marine ecosystems. A fundamental component of turbulent mixing is the separation of two nearby fluid elements, i.e., pair dispersion. Despite almost eighty years of intense scientific inquiry, no clear understanding of this fundamental aspect of turbulence has emerged. One critical unresolved question is the extent to which the initial separation of the fluid particles influences their subsequent motion. Surprisingly, our measurements in a laboratory water flow at very high turbulence levels (Taylor microscale Reynolds numbers up to R_lambda = 815) suggest that the initial separation remains important for all but the most violent flows on Earth. This observation has important consequences for such varied problems as pollution control, combustion modelling, hazardous chemical control, and even the understanding of how animals locate food, predators, and mates.

physics.flu-dyn↗