La presentazione è in caricamento. Aspetta per favore

La presentazione è in caricamento. Aspetta per favore

Tubo di Pitot. Flussi laminari e flussi turbolenti.

Presentazioni simili


Presentazione sul tema: "Tubo di Pitot. Flussi laminari e flussi turbolenti."— Transcript della presentazione:

1 Tubo di Pitot

2

3 Flussi laminari e flussi turbolenti

4 C.1.1 TURBOLENZA Turbolenza presente in molti campi dell’ingegneria (aerodinamica, diluizione di inquinanti, studio della scia a valle di un corpo in movimento, miscelazione e combustione in reattori chimici, moto dell’aria nell’apparato respiratorio e del sangue a valle di valvole cardiache, ecc.). Turbolenza: fenomeno non totalmente compreso ma non casuale: le statistiche della separazione di coppie di particelle (~t 3 ) sono diverse da quelle dei random walks (~t 1 ) (Ottino 1990). 6/ 19 PUNTO CRITICO IPERBOLICO PUNTO CRITICO ELLITTICO Approccio topologico: punti critici iperbolici ed ellittici, geometria frattale e strutture ad “8 in 8” (es.: Antonia et al. 1986, Davila & Vassilicos 2003).

5 C.1.2 TURBOLENZA 2D in oceano

6

7 Turbolenza quasi-bidimensionale (Q2D): importanza teorica (semplificazione della 3D ma anche peculiarità: conservazione lagrangiana della vorticità, cascata inversa dell’energia, ecc.) e pratica (es. previsioni atmosferiche, moto delle masse d’acqua negli oceani e nell’atmosfera). C.1.2 TURBOLENZA 2D in atmosfera GETTO 2D PUNTI CRITICI IPERBOLICI VORTICE E PUNTO CRITICO ELLITTICO 7/ 19

8 Measurement via PTVA of the acceleration on quasi-two-dimensional turbulent-like flows controlled by multi-scale electromagnetic forces Simone Ferrari (1)(2), Lionel Rossi (2) and John Christos Vassilicos (2) (1)(2)

9 1.2. Q2D EM controlled multi-scale flows Experimental set-up: a shallow layer of brine EM forced. Topology and forcing time-dependency are known and controlled. Power-law shaped energy spectrum and Richardson-like pair dispersion properties (Rossi et al., JFM 2006) in a laminar steady flow. Experiments: constant and time-dependent forcing. 4/ 17 Magnets’ size: 160 mm, 40 mm, 10 mmElectrodesElectrodesMagnets Tank size: 1700x1700 mm² Brine layer’s thickness: 5 mm ab cd Flow visualizations with constant forcing; (a, b, c: whole field; d: SW quarter) Stirring on the SW quarter (same flow on the left)

10 Constant forcingTime-dependent forcing Diluizione e turbolenza

11 15/ Time dependent flows Time dependent forcing with different frequencies, mean intensities and magnitudes, to excite different flow scales. A further step towards fully controlled turbulent-like flows. Expected time scales of the three scales of forcing t versus current I; M160, M40 and M10 refers to the magnets’ size; the black straight line identifies the current value over which the bottom friction is no more negligible. Mass exchange between small and medium scales is enhanced. Mass exchange between large and medium scales is enhanced.

12 10/ Results: measured trajectories Trajectories are measured at all the scales of the flow (stagnation points with three different length scales). Example of measured trajectories (8 runs): on the left the whole investigation field, on the right a zoom on the SW quarter MAGNETS’ POSITION = hyperbolic stagnation point = elliptical stagnation point large scales medium scales small scales

13 Dal Lagrangiano all’Euleriano

14 The mesh has 600x600 points with a mesh ’ s size of 3x3 pixels (resolution 4 times higher than PIV) 11/ Results: Eulerian fields VELOCIY: hyperbolic stagnation point; elliptical stagnation point ACCELERATION: “source”; “sink”;“spreader”

15 12a/ 17 Accelerazione Flusso con accelerazione locale nulla. L’accelerazione è alta dove sia la velocità che la deformazione sono alte. Accelerazione Velocità Deformazione

16 12b/ Results: Navier-Stokes equations’ terms A zoom on the SW quarter to highlight the physical coherence of the measures. Acceleration and viscous term in pixel/s 2, velocity in pixel/s; 1 pixel = mm This allows an indirect measure of the pressure gradient over all the investigation field. Velocity Acceleration Viscous term Acceleration is much larger than viscous term everywhere but at the small scales (like in turbulent flows).

17 3.4 Results: towards efficient mixing 14/ 17 u·au·a Power input and output, in pixel 2 /s 3 ; 1 pixel = mm Stirring intensity, in s -2 ; 1 pixel = mm Experimental measure of a over the whole investigation field. ·a·a Tools to optimize the power input according to the required mixing => efficient mixing. Stirring is stronger where a large and positive (Vassilicos, 2002): the points of highest stirring are not the ones connected to the largest power input. Local maxima of a correspond to acceleration sources, local minima of a correspond to acceleration sinks. MAGNETS’ POSITION The power input-output is closely related to the pressure term.

18


Scaricare ppt "Tubo di Pitot. Flussi laminari e flussi turbolenti."

Presentazioni simili


Annunci Google