3D reconstruction of a compressible flow by synchronized multi-camera BOS

Three-dimensional reconstruction of a microjet with a Mach disk by Mach–Zehnder interferometers

“…To obtain density data on shock-containing free jets, various non-intrusive experimental techniques have been presented in the past, including rainbow schlieren deflectometry (Satti et al 2007;Kolhe & Agrawal 2009;Takano et al 2016), background oriented schlieren (Venkatakrishnan 2005;Van Hinsberg & Rösgen 2014;Nicolas et al 2017), moiré schlieren (Tabei, Shirai & Takakusagi 1992) (Nicolas et al 2017), D e = 22 mm RSD (Takano et al 2016), D e = 10 mm MZI (Nakamura & Iwamoto 1996), D e = 10 mm Moire schlieren (Tabei et al 1992), D e = 6 mm FIGURE 12. Comparison among centreline density profiles of underexpanded sonic jets obtained by various optical diagnostics for NPR = 4.0.…”

“…Figure 12 shows a comparison between the density profiles along the jet centreline obtained using the various quantitative flow visualization methods for underexpanded sonic jets emitted from axisymmetric convergent nozzles under the same nozzle operating condition (NPR = 4) with different exit diameters. The density profiles normalized by the ambient density ρ b from Tabei et al (1992), Nakamura & Iwamoto (1996), Takano et al (2016) and Nicolas et al (2017) are superimposed on our measurement (indicated by the blue line) using the Mach-Zehnder interferometer and the numerical result (indicated by the red line) from the RANS simulation with the SST k-ω turbulence model. In order to make it easier to view, the precision error bars are removed from our experimental result and the theoretical density rise by a normal shock wave is also included as a reference.…”

“…The density profiles obtained from both the rainbow schlieren and the background schlieren show good quantitative agreement with the simulation over the entire region. It should be noted that the nozzle used by Takano et al (2016) is geometrically similar to that shown in figure 2, while the wall contour of the nozzle utilized by Nicolas et al (2017) is converged in the downstream direction at a constant half-angle of 30 • and followed by a short straight duct to provide a uniform sonic condition on the jet exit plane. From a comparison between the centreline density profile obtained by the present Mach-Zehnder interferometer and that by the rainbow schlieren deflectometry, it is important to note that there is almost no difference in effects of the nozzle size on the jet density field.…”

Vertical digital holographic bench for underexpanded jet gas density reconstruction

“…Interferograms are recorded at 10Hz for different Nozzle Pressure Ratio (NPR). The tomography based on the minimization of a least squared criterion regularized by Tikhonov by a conjugated gradients method similarly to [3] gives density reconstruction of instantaneous of the jet. The compression structures have a 3 dimensional shape has shown by the iso-densities represented in Fig.…”

Application of Rainbow Schlieren Deflectometry for Jets from Round Laval Nozzles Followed by Cylindrical Ducts

“…However, conventional schlieren techniques have been extensively applied for qualitative flow visualization because they take considerable effort to extract quantitative properties. On the other hand, recent methods for visualizing jet density fields quantitatively include laser-based interferometry such as Twyman-Green interferometry [2], Mach-Zehnder interferometry [3] [4] [5] or schlieren based optical techniques such as the background oriented schlieren (BOS) [5] [6], calibrated schlieren [7] [8], and rainbow schlieren deflectometry [7] [9] [10] [11]. Among them, the rainbow schlieren deflectometry would presumably be the simplest optical technique to acquire density fields of jets quantitatively.…”