Ultra-high-speed tomographic digital holographic velocimetry in supersonic particle-laden jet flows

Abstract

Ultra-high-speed tomographic digital holographic velocimetry is used to measure the three-component, three-dimensional velocities and trajectories of micron-sized particles in a supersonic underexpanded jet flow. In high-speed digital in-line holography, the depth resolution or depth of field is severely restricted by the limited resolution of the digital recording array, which leads to significant elongation of the reconstructed particles in the depth direction. It is shown that by applying tomographic digital holography, this limitation imposed by the high-speed recording array is relaxed and that the accurate reconstruction of 3D particle intensities is possible without the depth-of-field problem. This method is demonstrated by measuring 110 μm solid particles suspended in a ‘mildly underexpanded’ jet with a nozzle pressure ratio of 2.0. The interference pattern produced by both the suspended particles and the density gradient field is simultaneously recorded by two digital high-speed cameras at a frame rate of 500 000 fps with an exposure time of 250 ns. Individual object fields are reconstructed by tomographic holography and the velocity of the micron-sized particles is analyzed by cross-correlation particle tracking velocimetry. The accuracy of the particle velocity measurements is estimated to be within 5 m s−1 or approximately 4.5% of the particle velocity. In addition, the method is used to study the particle–flow interactions by means of coherent imaging, which reveals a complex interaction between the micron-sized particles and the flow structure of this high-speed 3D unsteady turbulent particle-laden flow.

Lactose microparticle formation from finely atomised droplets

“…B1 (Supplementary information). The second method involves recording the light diffraction facilities in the Mechanical Engineering Department in Monash University, as used elsewhere (Buchmann et al, 2013). A laser beam was expanded through a series of lenses and directed through the atomised spray onto a digital CCD camera which is equipped with a long-distance microscope lens with a magnification factor of 2.95 mm/pixel.…”

“…In micro-ball milling, the bulk powder is centrifugally rotated in a chamber with small metal balls which aid in the micronisation process (Bensebaa, 2013). Air jet milling, on the other hand, uses high air velocities to induce fracture on particles when they collide (Chamayou and Dodds, 2007).…”

“…While air-jet milling is suitable for producing micron-sized particles, this process requires considerable energy input in order to accelerate the particles to a velocity suitable for fracture (Chamayou and Dodds, 2007;Saravacos and Kostaropoulos, 2002). Moreover, inefficiencies of milling on soft material were also observed; a freezing process is sometimes required in order to reduce the elasticity of the material (Saleem and Smyth, 2010).…”

Direct particle depth displacement measurement in DHPTV using spatial correlation of focus metric curves

“…However, the particle depth displacement z Δ during a short interval t Δ in DHPTV is so small that even a small uncertainty z err in the depth location can be at the same order as z Δ and thus leads to an unacceptable velocity error. An alternative approach for accurate depth position is tomographically recording inline particle holograms using multiple CCD cameras [22,23].…”

Quantitative, three-dimensional imaging of aluminum drop combustion in solid propellant plumes via digital in-line holography

“…The magnification factor is determined using the method suggested in [15]. A glass slide containing dots with known spacing (Max Levy Autograph distortion target DA020) is placed within the DIH line-of-sight and traversed in the z direction until it is in focus at the front focal plane.…”