Search results for "turbulent"

Effective temperature and scaling laws of polarized quantum vortex bundles

2011

Abstract An effective non-equilibrium temperature is defined for (locally) polarized and dense turbulent superfluid vortex bundles, related to the average energy of the excitations (Kelvin waves) of vortex lines. In the quadratic approximation of the excitation energy in terms of the wave amplitude A, a previously known scaling relation between amplitude and wavelength k of Kelvin waves in polarized bundles, namely A ∝ k − 1 / 2 , follows from the homogeneity of the effective temperature. This result is analogous to that of the well-known equipartition result in equilibrium systems.

Effects of roughness on particle dynamics in turbulent channel flows: a DNS analysis

2014

AbstractDeposition and resuspension mechanisms in particle-laden turbulent flows are dominated by the coherent structures arising in the wall region. These turbulent structures, which control the turbulent regeneration cycles, are affected by the roughness of the wall. The particle-laden turbulent flow in a channel bounded by irregular two-dimensional rough surfaces is analysed. The behaviour of dilute dispersions of heavy particles is analysed using direct numerical simulations (DNS) to calculate the three-dimensional turbulent flow and Lagrangian tracking to describe the turbophoretic effect associated with two-phase turbulent flows in a complex wall-bounded domain. Turbophoresis is inves…

Turbulence structure and budgets in curved pipes

2013

Abstract Turbulent flow in curved pipes was investigated by Direct Numerical Simulation. Three curvatures δ (pipe radius a /curvature radius c ) were examined: δ  = 0 (straight pipe), simulated for validation and comparison purposes; δ  = 0.1; and δ  = 0.3. The friction velocity Reynolds number (based on the pipe radius a ) was 500 in all cases, yielding bulk Reynolds numbers of ∼17,000, ∼15,000 and ∼12,000 for δ  = 0, 0.1 and 0.3, respectively. The computational domain was ten pipe radii in length and was resolved by up to 20 × 10 6 hexahedral finite volumes. The time step was chosen equal to a wall time unit; 1 Large Eddy TurnOver Time (LETOT) was thus resolved by 500 time steps and simul…

Phenomenological description of sedimentation in turbulent vortex tangles

2008

The aim of this Brief Report is to provide a simple intuitive derivation of the results for sedimentation velocity of a small spherical particle in a counterflow vortex tangle in turbulent superfluid. When the velocity of the tangle vortex lines is small as compared to that of the particle, our results reduce to those obtained previously by other authors through more complex arguments, except for a logarithmic dependence of one of the coefficients on the vortex line density. Comparison of both derivations may be useful to clarify the range of validity of the expressions for the forces between the particle and the tangle.

Hydrodynamic Equations of Anisotropic, Polarized, Turbulent Superfluids

2009

Longitudinal counterflow in turbulent liquid helium: velocity profile of the normal component

2013

In this paper, the velocity profile of the normal component in the stationary flow of turbulent superfluid helium inside a cylindrical channel is determined, making use of a one-fluid model with internal variables derived from Extended Thermodynamics. In the hypothesis of null barycentric velocity of the fluid (the so-called counterflow situation) it is seen that, in the presence of a sufficiently high vortex length density, the velocity profile of the normal component becomes very flat in the central region of the channel. Thus, a central flat profile of the normal fluid does not necessarily imply that the flow of the normal component is turbulent.

Turbulent mixing and dispersion mechanisms over flexible and dense vegetation

2019

The present study investigates flow turbulence and dispersion processes in the presence of flexible and dense vegetation on the bed. The turbulent dispersion coefficients and the terms of the turbulent kinetic energy equation are determined by using data collected in a straight laboratory channel with living vegetation on the bed. Results show that the turbulent integral lengths assume an order of magnitude comparable to the stems’ characteristic dimension independently by the direction and the turbulence assumes an isotropic behavior. The coefficients of dispersion have a trend similar to that of the turbulent lengths and assume low values in the longitudinal, transversal and vertical dire…

The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows

2008

Wall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric para…

EXPERIMENTAL STUDY ON THE FLUID FLOWIN THE CONDUCTS

2018

Fluids are high mobility environments that, under the action of external forces, are continuously and irreversibly deformed. The flow of fluid through a pipe is ensured by a pressure difference between its ends. The presented paper aims to experimentally determine the velocity profile of flowing a Newtonian fluid through a circular section pipe by measuring the local speed at five points on the pipe radius.

Numerical prediction of turbulent flow and heat transfer in helically coiled pipes

2010

Abstract Computational results were obtained for turbulent flow and heat transfer in curved pipes, representative of helically coiled heat exchangers. Following a grid refinement study, grid independent predictions from alternative turbulence models ( k – ɛ , SST k – ω and RSM– ω ) were compared with DNS results and experimental pressure drop and heat transfer data. Using the SST k – ω and RSM– ω models, pressure drop results were in excellent agreement with literature data and the Ito correlation. For heat transfer, the literature is not comparably complete or accurate, but a satisfactory agreement was obtained in the range of available data. Unsatisfactory results, both for pressure drop …