Four Decades of Utilizing Shadowgraph Techniques to study Natural Convection in Cavities: Literature Review

Characterization of Supersonic Compressible Fluid Flow Using High-Speed Interferometry

“…Therefore, time stability was examined. As aforementioned, we captured 50 frames during one measurement sequence, taking 50 ms, and used averaged phase maps ∆ϕ for further processing-see (12). However, the standard deviation,…”

“…Moreover, contactless optical methods do not disturb the flow field. Due to the presence of density gradients, compressible fluid flow is very suitable for an investigation using optical methods that are sensitive either to the refractive index of the medium through which the light wave propagates (interferometry), or to a refractive index gradient in the medium (schlieren [7][8][9][10][11], shadowgraph [12][13][14][15][16], Moiré deflectometry [17][18][19][20][21]). Interferometric methods such as classical interferometry [22,23], holographic interferometry [24] and digital holographic interferometry [25][26][27][28][29] stand as the most accurate optical techniques [26,30,31] that are applied in many sectors of industry and scientific research, notably in the study of liquid cooling [32], diffusion [33], convection [34,35], temperature measurements and visualization [1,25,36], temperature fields measurement in pulsatile jets [25], studies of living cell imaging [37,38], precision measurement [15,39,40], vibrometry [41,42] etc.…”

Work-in-Progress: Visualization and Simulation of the Thermal Boundary Layer around a Cylinder as a Classroom Demonstration

“…Shadowgraphy is a research method developed and used for decades by scientists for flow visualization [12] but there is no reason it cannot be applied as an effective learning tool in classroom teaching of heat transfer. The shadowgraph technique is the least expensive and the simplest optical method that can be used for flow visualization in transparent media like air or water.…”

“…Hence, refracted light rays cast a shadow with varying light intensity to produce the shadowgraph. After passing through the fluid, the light beam may be projected onto a screen or can be refocused by another lens or mirror and recorded by a CCD camera [12,13].…”

“…The shadowgraph visualization setup is simple, including a point light source, a couple of mirrors or lenses, a screen or a CCD camera to capture the images [12]. Instead of a point light source along with a mirror or lens to make a parallel beam of light, we use a collimated LED light source, and a machine-vision camera with a telecentric lens, that only receives light rays parallel to the optical axis, is used instead of a screen and a lens or mirror to refocus the image.…”