238 research outputs found
Hysteresis phenomenon in turbulent convection
Coherent large-scale circulations of turbulent thermal convection in air have
been studied experimentally in a rectangular box heated from below and cooled
from above using Particle Image Velocimetry. The hysteresis phenomenon in
turbulent convection was found by varying the temperature difference between
the bottom and the top walls of the chamber (the Rayleigh number was changed
within the range of ). The hysteresis loop comprises the one-cell
and two-cells flow patterns while the aspect ratio is kept constant (). We found that the change of the sign of the degree of the anisotropy of
turbulence was accompanied by the change of the flow pattern. The developed
theory of coherent structures in turbulent convection (Elperin et al. 2002;
2005) is in agreement with the experimental observations. The observed coherent
structures are superimposed on a small-scale turbulent convection. The
redistribution of the turbulent heat flux plays a crucial role in the formation
of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres
Legitimiteit gezocht: dilemma’s van democratische afstand en nabijheid in het RES-proces
The Legitimacy and Effectiveness of Law & Governance in a World of Multilevel Jurisdiction
ACE Inhibition in Anti-Thy1 Glomerulonephritis Limits Proteinuria but Does Not Improve Renal Function and Structural Remodeling
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An application of tomographic PIV to investigate the spray-induced turbulence in a direct-injection engine
Fuel sprays produce high-velocity, jet-like flows that impart turbulence onto
the ambient flow field. The spray-induced turbulence augments fuel-air mixing,
which has a primary role in controlling pollutant formation and cyclic
variability in engines. This paper presents tomographic particle image
velocimetry (TPIV) measurements to analyse the 3D spray-induced turbulence
during the intake stroke of a direct-injection engine. The spray produces a
strong spray-induced jet in the far field, which travels through the cylinder
and imparts turbulence onto the surrounding flow. Planar high-speed PIV
measurements at 4.8 kHz are combined with TPIV at 3.3 Hz to evaluate spray
particle distributions and validate TPIV measurements in the particle-laden
flow. An uncertainty analysis is performed to assess the uncertainty associated
with vorticity and strain rate components. TPIV analyses quantify the spatial
domain of the turbulence in relation to the SIJ and describe how turbulent flow
features such as turbulent kinetic energy, strain rate and vorticity evolve
into the surrounding flow field. Access to the full tensors facilitate the
evaluation of turbulence for individual spray events. TPIV images reveal the
presence of strong shear layers (visualized by high S magnitudes) and pockets
of elevated vorticity along the immediate boundary of the SIJ. Values are
extracted from spatial domains extending in 1mm increments from the SIJ.
Turbulence levels are greatest within the 0-1mm region from the SIJ boarder and
dissipate with radial distance. Individual strain rate and vorticity components
are analyzed in detail to describe the relationship between local strain rates
and 3D vortical structures produced within strong shear layers of the SIJ.
Analyses are intended to understand the flow features responsible for rapid
fuel-air mixing and provide valuable data for the development of numerical
models
Surface pressure and aerodynamic loads determination of a transonic airfoil based on particle image velocimetry
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