1,720,968 research outputs found
Lifetime of turbulent patch in Taylor Couette setup
No full textIn linearly stable shear flows like pipe and plane Couette flows, the transition from the laminar to the turbulent regime occurs abruptly. To better understand this transition, the time evolution of turbulent patches, created by controlled finite amplitude perturbations, have been studied in the literature. These studies mostly focused on pipe flows for which a finite lifetime of the patch was proven. The same conclusion was drawn in the only available study performed in a Taylor Couette setup. Here, we measured the lifetime in a different size TC setup. We show that the lifetime is indeed finite and also very sensitive to the boundary condition, but not much to the perturbation mechanism. We suggest that in addition to the Reynolds number, the lifetime depends on the aspect ratio to the radius ratio of the setup
Experimental study of surface modification in a fully turbulent Taylor-Couette flow
No full textFriction measurements were performed in a Taylor-Couette setup. Drag reduction was obtained with a riblet surface and indicated a drag reduction for a wide range of shear Reynolds numbers, with a maximum of 5.3% at Re_s=47000 (s+=14). Tomographic PIV verified that the friction coefficients are strongly related to the flow regimes and structures. The bulk fluid rotation was changed by the application of the riblets, as the wall-bounded flow conditions at the inner cylinder wall were changed due to the surface modification and is called the rotation effect. A simple model was used to indicate the averaged bulk velocity shift (1.4%), after which the drag changes due to the rotation effect (-1.9%) and the riblet effect (-3.4%) were determined. The bulk velocity shift of 1.4% was verified by PIV measurements. Compliant surfaces will be further investigated to check their required conditions for drag reduction of wall-bounded flow
Measurement of turbulent mixing in an axis-symmetric oil-water jet of micro-droplets: macroscopic and microscopic flow processes
No full textPIV-Velocimetry measurements in liquid-liquid flow simultaneously in both phases by Refractive Index Matching
No full textDrag and Power-loss in Rowing Due to Velocity Fluctuations
No full textAbstractThe flow motions in the turbulent boundary layer between water and a rowing boat initiate a turbulent skin friction. Reducing this skin friction results in better rowing performances. A Taylor-Couette (TC) facility was used to verify the power losses due to velocity fluctuations PV′ in relation to the total power , as a function of the velocity amplitude A. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency eV . The velocity efficiency eV for a typical rowing velocity amplitude A of 20 – 25% was about 0.92 – 0.95%. Suppressing boat velocity fluctuations with 60% will increase boat speed with 1.6%. Riblet surfaces were applied on the inner and outer cylinder wall to indicate the drag reducing ability of such surfaces. The results of the measurements at constant velocity are identical as the results reported earlier, while the experimental configuration was different. This confirms once more the consistency of the TC-system for drag studies. The maximum drag reduction DR was 3.4% at a Reynolds number Res 4.7 × 104, which corresponds to a shear velocity in this TC-system with water of V 4.7 m/s. For typical rowing velocity fluctuations, the riblets maintain to reduce the drag with 2.8% and corresponds to a averaged velocity increase of 0.9%. The drag reducing ability of riblets is partly lost due to velocity fluctuations with high amplitudes (A > 20%). From these results, it is concluded that the friction coefficient Cf will vary within one cycle. Higher acceleration/deceleration leads to a additional level of turbulent kinetic energy
Experiments on air entrainment from a stationairy slug bubble in a vertical tube
No full textMechanical Maritime and Materials Engineerin
Design study for the Measurement Section & Diffuser optimisation for the TU Delft cavitation tunnel
No full textA too small optical accessible area of the old Measurement Section of the Cavitation tunnel made monitoring the upcoming experiments, with for instance high speed cameras, impossible. This was its main imperfection. A proper amount of optical accessible area needed lead too this conversion. The new Measurement Section designed has an optical accessible area which is sufficient for the experiments. It was needed to have a zero velocity-, and pressure gradient over the new Measurement Section. The displacement thickness of the boundary layer which narrows effectively the inner of the Measurement Section would lead to acceleration of the flow and therefore needed to be compensated. This was done by gradually descending the bottom plate of the new Measurement Section over its length, since the side walls of the new Measurement Section had to be parallel for a constant distance of the camera to the side walls over its total length.Fluid MechanicsSolid & Fluid MechanicsMechanical, Maritime and Materials Engineerin
Breakup of polystyrene particles in turbulent Taylor-Couette flow: Vallidation of a DNS model for asphaltene agglomeration
No full textThe study of polystyrene particles in Talor-Couette flow for the vallidation of a DNS code for asphaltene agglomerationsolid and fluid mechanicsProcess and EnergyMechanical, Maritime and Materials Engineerin
Transition to turbulence in Taylor Couette flow
No full textThe most recent studies of intermittent state in linearly stable shear flows, like pipe, Plane Couette and Taylor Couette flow, have shown that turbulent structures, created by finite-amplitude perturbation, have an exponential distribution of the lifetimes. Here we experimentally examine the lifetime of turbulent spot in Taylor Couette flow (with stationary inner cylinder) for different perturbation mechanisms and different boundary conditions. We show that for all of these cases, the decay of the turbulent spot can be described by Poisson process, which supports the chaotic transient model for this flow. Furthermore, we show that characteristic lifetime of the turbulent spot increases with Reynolds number faster than exponentially, but does not diverge to infinity. This is in agreement with the most recent studies in pipe and Taylor Couette flows and implies that turbulence is a transient state for all Reynolds numbers (before the global bifurcation). Finally, we show that there is a universal behavior for the characteristic lifetime of the intermittent state in Taylor Couette flow with stationary inner cylinder. This universal series is obtained using critical Reynolds number and aspect ratio as scaling parameters.Solid and Fluid MechanicsMechanical EngineeringMechanical, Maritime and Materials Engineerin
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