Abstract
The Mach–Zehnder interferometer with the finite fringe setting is applied for a shock-containing microjet issued from an axisymmetric convergent nozzle with an inner diameter of 1.0 mm at the exit. Experiments are performed at a nozzle pressure ratio of 3.0 to produce a slightly underexpanded sonic jet where the Reynolds number, based upon the diameter and flow properties at the nozzle exit, is 4.45 times 10^4. The reconstruction of the jet density field is performed using the Abel inversion method under the assumption of an axisymmetric flow as well as the Fourier transform method for the phase shift analyses of interferograms. The three-dimensional density field of a shock-containing microjet can be captured with a spatial resolution of 4 upmum, and the near-field shock structure inside the jet plume is shown in the density contour plot at the cross-section including the jet centerline. In addition, the density field of the microjet is illustrated with various techniques, including representation such as the vertical-knife-edge schlieren, the horizontal-knife-edge schlieren, the bright-field schlieren, and the shadowgraphy. In addition to experiments, the Reynolds averaged Navier–Stokes (RANS) simulation with the SST k–omega turbulence model is carried out to model the microjets, and a quantitative comparison with the experiments is performed. The jet centerline density profile obtained by the present experiment is quantitatively compared with those from the previous Mach–Zehnder interferometer, the background oriented schlieren, as well as the RANS simulation.
Highlights
Since the pioneering research of Scroggs and Settles (1996), there has been considerable experimental research on the subject of the dynamics of a supersonic microjet for the application of microscale devices
The flow structures of a microjet with weak shocks were investigated by the Mach–Zehnder interferometer with the finite-fringe setting
We observe that the density field in the compression regions of the first three shock-cells has two local maxima at locations away from the jet centerline, which has not been reported by other studies
Summary
Since the pioneering research of Scroggs and Settles (1996), there has been considerable experimental research on the subject of the dynamics of a supersonic microjet for the application of microscale devices. The structures of supersonic microjets were systematically studied for the first time by Scroggs and Settles (1996), who made axisymmetric nozzles with exit Mach numbers ranging from 1.0 to 2.8 and two different inner diameters of 600 μ m and 1200 μ m at the nozzle exit They measured the Pitot pressures along the jet centerline by impinging the jet upon at a plate, including a pressure port of 0.2 mm in diameter with a pressure sensor attached to the reverse side. Phalnikar et al (2008) fabricated a micro Pitot probe with a pressure hole of 50 μ m in diameter, and later, Aniskin et al (2013) developed one with an intake port of 12 μ m diameter These two research groups performed the Pitot pressure measurements to study the size of shock cells and the supersonic core length of the microjet. With complex shock-containing structures, a proper and homogeneous seeding is very difficult
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