Search results for "laminar"
showing 10 items of 112 documents
Collision efficiencies empirically determined from laboratory investigations of collisional growth of small raindrops in a laminar flow field
2007
In laboratory experiments at the vertical wind tunnel of the University of Mainz the collisional growth of drops with radii between 70 and 170 μm in radius were observed while the collector drop freely floated in a cloud of droplets with radii ranging from 1 to 7 μm. Previously existing tables with collision efficiency values were interpolated and completed in such a way that drop growth rates calculated with these collision efficiencies match with observed growth rates. These new tables provide collision efficiency values for a wide range of drop sizes and radius ratios p including those ranges where efficiency values missed so far. This is of high importance for small p-ratios where the c…
Analysis of the static and dynamic behaviour of a magnetic liquid seal
1985
A rotating shaft seal, using ferrofluid between biconical truncated magnetic poles, is analysed both in static and dynamic conditions. After solving Laplace's equation and allowing an approximate expression for the magnetic potential, the magnetic forces acting on the working fluid are obtained. It is thus possible to determine the baric field existing in static conditions and the highest tolerable pressure jump. In the case of dynamic working the flow is schematized by two interior regions, where the azimuthal velocity prevails, and four boundary layers on the walls, where meridional transport of fluid takes place. Assuming laminar motion, by means of a perturbation procedure it is possibl…
3D MHD lead–lithium liquid metal flow analysis and experiments in a Test-Section of multiple rectangular bends at moderate to high Hartmann numbers
2013
Abstract Experiments with liquid lead–lithium (Pb–Li) were carried out in a stainless steel (SS) Test Section (TS) consisting of multiple 90° bends for various flow rates and applied magnetic fields of up to 4 T. Characteristic MHD flow parameter Hartmann number, Ha ( = B 0 a σ / μ , Ha2 is the ratio of electromagnetic force to viscous force) and interaction parameter, N ( = σ a B 0 2 / ρ U , N is the ratio of electromagnetic force to inertial force) of these experiments were varied from Ha = 515 to 2060 and N = 25 to 270 by changing the applied magnetic field and flow rates respectively. Three dimensional numerical simulations have been carried out using MHD module of FLUENT code. The meas…
Unsteady turbulence in plane channel flow
2011
Abstract Direct numerical simulations were conducted for oscillating flow with zero time mean (reciprocating flow) in a plane channel subject to a harmonic forcing term of varying amplitude and frequency. The results confirmed the existence of four flow regimes (laminar, “disturbed laminar”, intermittently turbulent, and fully turbulent) depending on the above parameters. The flow behaviour was found to depend on the complex interplay of mean and turbulence quantities, as described by the closed loop formed by the streamwise Reynolds-averaged momentum equation in conjunction with the exact transport equations for the turbulent (Reynolds) stresses. A crucial role in this loop appeared to be …
Dynamics of the transition from polarization disorder to antiphase polarization domains in vector fiber lasers
2014
We demonstrate that nonlinear polarization coupling in a fiber ring laser without polarization-selective elements, subject to the effects of average anomalous dispersion, Kerr effect, and nonlinear gain saturation, can lead to the antisynchronization of spatiotemporal chaos into a wide variety of ordered laminar states of orthogonal polarization temporal domains. These antiphase polarization domains include stable lattices of soliton trains with high duty cycle at repetition rates of hundreds of MHz, as well as sparse trains of coupled dark and bright solitary waves.
Effective thermal conductivity of superuid helium: Laminar, turbulent and ballistic regimes
2016
Abstract In this paper we extend previous results on the effective thermal conductivity of liquid helium II in cylindrical channels to rectangular channels with high aspect ratio. The aim is to compare the results in the laminar regime, the turbulent regime and the ballistic regime, all of them obtained within a single mesoscopic formalism of heat transport, with heat flux as an independent variable.
Prediction of Swirling Flow in a Corrugated Channel
1991
Laminar and turbulent flow in a corrugated channel is simulated using HARWELL-FLOW3D. The channel represents a typical cell within a proposed design for the heat-transfer element of a rotary regenerator. Velocity vectors in planes perpendicular and parallel to the axis of a corrugation are visualised using Harwell’s graphics package, OUTPROC. Both programs were mn on Harwell’s Cray 2. The velocity vector plots show clear evidence of swirl, which is thought to be the mechanism responsible for the high rates of heat transfer in this type of heat-exchanger geometry. The swirl strength is shown to be a function of the channel geometry.
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…
Types I and II intermittencies in a cascade laser model
1995
Abstract We report on types I and II intermittencies found in a cascade laser model. A continuous transition from one to another type of intermittency, which involves the coexistence of both types of laminar phases within the same time series, is found. Type II intermittency has special characteristics such as its origin at a frequency locked two-torus. When frequency unlocked this torus bifurcates to a three-torus, further giving rise to a type II intermittent like behaviour with new features during the laminar phases.
A Wind Tunnel Study of the Effects of Turbulence on the Growth of Cloud Drops by Collision and Coalescence
1999
A set of wind tunnel experiments was carried out to investigate the growth of single drops by collision coalescence with small droplets in laminar and turbulent flow. Analysis of the experiments shows that under otherwise similar conditions, there exists a tendency toward a faster drop growth under turbulence. The observed growth under laminar conditions agrees well with computed continuous growth of a collector drop using collision efficiencies reported in the literature.