1,721,126 research outputs found
Alessandro Bosi, Premessa, in Anita Gramigna, Marco Righetti, Carlo Rosa, Estetica della formazione. La conoscenza nella bellezza, Unicopli, Milano 2008, pp. 9-16.
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Experimental study of the flow field over bottom intake racks
No full textBottom racks made by longitudinal bars are hydraulic structures widely adopted for engineering purposes. In the present paper we revisit the problem of their hydraulic design, analyzing the data obtained from a systematic series of experiments carried out in a laboratory flume. For each run we measured the diverted discharge, the water surface longitudinal profile, and using a two-dimensional backscatter laser Doppler anemometer, we measured the velocity field over the rack and in the slit between two adjacent bars. The latter measurements, in particular, allow us to obtain the along-rack distributions of the discharge coefficient to be used to determine the rate of change of the diverted discharge. We use such distributions to derive a physically based relationship relating the overall diverted discharge to the length of the rack, the void ratio, the discharge coefficient measured under static conditions, the specific head of the stream approaching the rack, and a modified Froude number. The robustness of the proposed relationship is confirmed by the comparison between the discharges calculated through the proposed relationship and those measured in an extensive series of experiments available in the literature, characterized by ranges of the relevant flow parameters much larger than those investigated in the present contribution
Closure to "Experimental Study of theFlow Field over Bottom Intake Racks" byMaurizio Righetti and Stefano Lanzoni
No full textParticle-fluid interactions in a horizontal near-wall turbulent flow
No full textThe role of particles heavier than the fluid (glass spheres in water) in a turbulent open channel flow over a smooth bed is examined at volume concentration about 10−3. The
present work focuses on the dynamical interaction between the solid (particles) and the fluid phases in the near-wall region. Experimental measurements have been performed
by means of phase Doppler anemometry to acquire two velocity components, particle size and concentration data simultaneously; the Reynolds number of the flow was
close to 15 000. It is observed that in the particle-laden flow, the vertical profiles of the streamwise mean velocity (for both fluid and solid phases) are reduced in the outer
layer (y+ >20), but increased in the viscous sublayer (y+ <5) in comparison to the clear-water conditions, leading to an apparent slip kinematic boundary condition close
to the wall (y+ ≈2). Moreover, in the presence of solid particles, the flow exhibits a velocity close to the wall (y+ <15) which is smaller than that of the particles, while in
the outer layer the opposite takes place. In particle-laden flow, turbulence intensities of the streamwise and especially of the vertical velocity are damped for y+ >10–20
(depending on particle inertia) but enhanced in the very near-wall region (y+ <5), as is the Reynolds stress. These findings can be explained if they are referred to the
mechanism of particle entrainment and deposition, which takes place close to the wall. This mechanism is related to particle inertia and to the dynamic of the structure
of near-wall turbulence, which connects the buffer and outer regions with the very near-wall region. A significant momentum exchange between the two phases, which
is particularly effective in the buffer region, is revealed by the quadrant analysis of the Reynolds stresses.
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Roma, paesaggi contemporanei
No full textAtti del convegno di studi (Sapienza, Università di Roma 28-30 maggio 2008
Pump-as-turbine for Energy Recovery Applications: The Case Study of An Aqueduct
Full text linkPump-as-Turbine (PaT) technology is taking the field in different small-hydro or energy recovery applications. These machines can be installed in water distribution grids to have pressure levels adjustment and electrical energy production. A PaT working in turbine mode has a different best efficiency point due to a variation of the fluid-dynamic operating conditions. In this paper, laboratory tests are performed to investigate its performances in pump and turbine mode. Hydraulic efficiency, torque and mechanical power are evaluated in several load conditions. In conclusion, an energy evaluation is shown considering a test case of a water distribution grid
A semi-implicit scheme for 3D free surface flows with high-order velocity reconstruction on unstructured Voronoi meshes
No full textIn this paper, we present a computationally efficient semi-implicit scheme for the simulation of three-dimensional hydrostatic free surface flow problems on staggered unstructured Voronoi meshes. For each polygonal control volume, the pressure is defined in the cell center, whereas the discrete velocity field is given by the normal velocity component at the cell faces. A piecewise high-order polynomial vector velocity field is then reconstructed from the scalar normal velocities at the cell faces by using a new high-order constrained least-squares reconstruction operator. The reconstructed high-order piecewise polynomial velocity field is used for trajectory integration in a semi-Lagrangian approach to discretize the nonlinear convective terms in the governing PDE. For that purpose, a high-order Taylor method is used as ODE integrator. The resulting semi-implicit algorithm is extensively validated on a large set of different academic test problems with exact analytical solution and is finally applied to a real-world engineering problem consisting of a curved channel upstream of two micro-turbines of a hydroelectric power plant. For this realistic case, some experimental reference data are available from field measurements. © 2012 John Wiley & Sons, Ltd
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