Op#cal Methods (flow visualiza#on, fluid density, concentra#on and temperature) Václav Uruba CTU Prague, AS CR VISUALISATION September 30, 2014 2 Visualisa<on • Surface par<cles • Flow par<cles – Volume par<cles distribu<on + light sheet – Volume illumina<on + localized par<cles • Fluid density September 30, 2014 3 Visualisa<on • We see streaklines and not streamlines • Laminar: streaklines = streamlines • Turbulent: streaklines ≠ streamlines x2 ⎣⎡ x1 (t ) , x2 (t )⎦⎤ u ( x,t ) ⎡⎣ x1 (t0 ) , x2 (t0 )⎤⎦ x1 September 30, 2014 x2 x1 4 Flow Visualiza<ons • On a solid surface – – – – – – – Oil flow Sublima<on Sand erosion Wall tuPs Oil dots Oil streaks Wall dye steaks • On a free surface (water table) – Surface bubbles – Hydraulic analogy (surface waves) – Hydraulic analogy (Water colors) • In a 3D space – – – – – – TuPs in air (grid, pole) Smoke in air Colored smoke (smoke wire) Laser sheet & smoke Dye in water: color streaks, or all water Hydrogen bubbles in water September 30, 2014 5 Oil Flow “surface streamlines” , i.e. surface shear stress lines top view – VKI L2-‐A wind tunnel, 28cm x 28cm, 40 m/s September 30, 2014 6 Coloured Oil Flow “surface streamlines”, separa#on in front of cylinder on flat plate September 30, 2014 7 Sand Erosion for Urban Microclimate Courtesy of D.Olivari, ~1990 VKI L1-‐B wind tunnel, 3 m x 2m Courtesy of J. Van Beeck, ~2006 VKI L2-‐B wind tunnel, 35 cm x 35 cm Sand erosion zones , i.e. zones of high intensity ground wind top view – VKI L1-‐B & L2-‐B wind tunnels September 30, 2014 8 Surface TuPs Tu`s indica#ng wind direc#on air intake in turbine engine pod VKI L1-‐A wind tunnel, 3m diam, 60 m/s September 30, 2014 9 Surface TuPs Tu`s direc#on indica#ng posi#on of stagna#on point VKI L1-‐A wind tunnel, 3m diam, 60 m/s Leading Edge of AEA B-‐737 wing September 30, 2014 10 Oil Streaks Oil streaks indica#ng velocity Hypersonic delta wing VKI Longshot tunnel, 42cm diam, Mach = 14 September 30, 2014 Courtesy of B. Richards, ~1970 11 Coloured Oil Streaks Coloured oil streaks indica#ng flow pafern Squealer-‐#p turbine blade, VKI CT-‐2 cascade facility September 30, 2014 Courtesy of T. Hofer & T. Arts, 2009 12 Water Tunnel – Coloured Streaks Coloured wall streaks – Triangular fin on flat plate VKI Water Tunnel, 12cm x 24 cm -‐ 0,1 m/s September 30, 2014 Ref. V. Ypersiel, S. Zemsch, M. Carbonaro VKI-‐U-‐1993-‐01 13 Water Table – Surface Soap Bubbles Turbulent unsteady wake in vortex-‐shedding flowmeter September 30, 2014 VKI Christmas postcard, test by M. Carbonaro, ~1978 14 Water Table – Surface Soap Bubbles Turbulent wakes downstream water collectors in cooling towers September 30, 2014 15 Supercri<cal Water Table – Surface Waves Choked and non-‐choked hypersonic intake September 30, 2014 16 Real-‐life “Water Table” – Surface Waves Front bow shock, side shocks at wheels and wake recompression shocks Flood in Milano, “Corriere della Sera” sept.2010 September 30, 2014 17 TuPs in air Hand-‐held s#ck with wool tu`, to explore flow field September 30, 2014 18 Smoke Streaks Flow across open door due to temperature difference between rooms September 30, 2014 19 Smoke Streaks For adver#sing purposes only…obvious streamline behaviour September 30, 2014 20 Smoke plumes Forced-‐dra` cooling tower plumes VKI L1-‐A wind tunnel, 3m diam. September 30, 2014 21 Smoke Wire – Coloured Smoke Sheets Secondary Flows in Turbine Cascade -‐ VKI special set-‐up Ref. C. Sieverding & P. Van Den Bossche, J. Fluid Mechanics, vol 134, 1983 September 30, 2014 22 Laser Sheet Enhanced Smoke Flow Vor#cal wake behind a delta wing VKI L-‐7 Wind Tunnel, 16cm x 16 cm, ~20 m/s September 30, 2014 23 Dye Streaks in Water Bluff protuberance on flat plate – landing gear pod VKI Water Channel 12 cm x 24 cm, ~2 cm/s September 30, 2014 24 Dye Streaks in Water Bluff protuberance on flat plate – landing gear pod VKI Water Channel 12 cm x 24 cm, ~2 cm/s September 30, 2014 25 Dye Streaks in Water Bluff protuberance on flat plate – landing gear pod VKI Water Channel 12 cm x 24 cm, ~2 cm/s September 30, 2014 26 Dye Streaks in Water Tunnel Body vor#ces on leeward side of missile at incidence – side view VKI Water Tunnel, 12 cm x 24 cm, ~5 cm/s September 30, 2014 27 Dye Streaks in Water Tunnel Body vor#ces on leeward side of missile at incidence – top view VKI Water Tunnel, 12 cm x 24 cm, ~5 cm/s September 30, 2014 28 Fluorescent Dye Streak & Laser Sheet Karman vortex street behind circular cylinder VKI Water Tunnel, 12cm x 24 cm, ~5 cm/s September 30, 2014 29 Hydrogen Bubbles in Water Wakes behind prongs of a scaled-‐up hot wire probe VKI Water Channel, 12cm x 24 cm, 10cm/s September 30, 2014 30 Hydrogen Bubbles in Water “Time-‐Lines” of periodically excited transi#onal boundary layer VKI Water Tunnel, 12cm x 24 cm, ~5cm/s Vibra#ng ribbon 85Hz, #me-‐lines 30 Hz September 30, 2014 31 DENSITY EVALUATION September 30, 2014 32 Density evalua<on • For variable density flows – High veloci<es – compressibility – Temperature fields • Methods – Shadowgraph – Schlieren – Interferometry September 30, 2014 33 Refrac<on index • Density ≈ Refrac<on index • Clausius-‐Mosog: n −1 = K ρ Refrac<on index Density Gladstone-‐Dale constant Air: K = 0,226 cm3/g September 30, 2014 34 Refrac<on index • Density ≈ Refrac<on index • Clausius-‐Mosog: n −1 = K ρ Refrac<on index Density Gladstone-‐Dale constant Air: K = 0,226 cm3/g September 30, 2014 35 Dvořák 1880 September 30, 2014 Shadowgraph Density 2nd spa<al deriva<ve 36 Foucalt 1859, Toepler 1864 September 30, 2014 Schlieren Density 1st spa<al deriva<ve 37 Zehnder 1891, Mach 1892 Density distribu<on Mach-‐Zehnder interferometer Schlieren September 30, 2014 38 LASER SHEET TECHNIQUES September 30, 2014 39 Laser sheet techniques • • • • • Par<cle Image Velocimetry (PIV) Laser-‐Induced Fluorescence (PLIF) Laser-‐Induced Incancescence (LII) Interferome<c Par<cle Imaging (IPI) Rayleigh Thermometry September 30, 2014 40 LASER INDUCED FLUORESCENCE LIF, PLIF September 30, 2014 41 Planar Laser Induced Fluorescence September 30, 2014 42 Laser-‐Induced Fluorescence Excited Molecule Photon Fluorescence Emission Excited State • Species selective measurements (OH, formaldehyde, fuel tracers, etc.) Ground State Absorption September 30, 2014 43 Laser-‐Induced Fluorescence Laser line Bandpass filter Normalised intensity 1,0 0,8 Fluorescence spectrum Absorp<on spectrum 0,6 Detected LIF 0,4 Residual laser light 0,2 0 200 250 300 350 400 450 500 550 600 Wavelength /nm l September 30, 2014 44 Planar Laser-‐Induced Fluorescence Detector Flame Light Sheet Op<cs September 30, 2014 45 Combus<on LIF system UV Camera Lens Optical Filter Image Intensifier CCD Camera Nd:YAG Laser Burner Sheet Optics September 30, 2014 Dye Laser 46 PLIF instantaneous mean variance September 30, 2014 47 LIF in Combus<on • • • • Gas with chemical reac<ons Produc<on of radicals Qualita<ve concentra<on of radical – OH – CH – NO – etc Concentra<on of larger molecules/tracers – Formaldehyde – Acetone – etc September 30, 2014 48 LASER-‐INDUCED INCANCESCENCE LII September 30, 2014 49 Laser-‐Induced Incancescence LII intensity (a.u.) • Soot par<cles are heated up by laser radia<on • The increased par<cle temperature results in increased emission of Plank radia<on Size decreases 0 100 200 300 400 500 Time (ns) September 30, 2014 50 Laser diagnos<cs in an IC engine September 30, 2014 51 Quan<ta<ve LII Soot volume fration (ppm) Soot-‐volume-‐frac<on in a Diesel engine • Soot formation at different EGR rates • Soot formation at different piston bowl geometries Work done at Combustion Physics, Lund University, Sweden September 30, 2014 52 INTERFEROMETIC PARTICLE IMAGING September 30, 2014 53 IPI • Interferometric detec<on of light scaqered and refracted from individual par<cles • Evalua<on of par<cles size • Could be combined with PIV September 30, 2014 54 IPI principle Focused image Defocused image Processed Valida<on Focused Defocused September 30, 2014 55 RAYLEIGH THERMOMETRY September 30, 2014 56 What is Rayleigh scattering? • Elastic scattering of light - Mie scattering: Dparticle >> λ - Rayleigh scattering: Dparticle < λ • All molecules contribute to the Rayleigh scattering, thus species specific measurements are not possible. • Blue light is scattered more efficiently than red light September 30, 2014 57 Rayleigh Thermometry • The Rayleigh signal is dependent on: - Laser intensity - Scattering cross section - Number density • If species composition and pressure are known in the gas the gas temperature can be determined from imaging of the Rayleigh scattering. September 30, 2014 58 Rayleigh Thermometry results Takes into account: • Scattering cross-section • Pressure • Laser pulse energy September 30, 2014 59 A last good advice... September 30, 2014 60
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