Application of particle image velocimetry and the background-oriented schlieren technique in the high-enthalpy shock tunnel Göttingen

Visualization of Shock Train-Boundary Layer Interaction in Mach 2.5 Isolator Flow

“…11 The constant diameter dot sizing corresponded to 3-5 pixel diameter dots when imaged allowing for sub pixel accuracy, while variable density gradient magnitudes in separate regions of the flow required a variation in interrogation window sizing. BOS has furthermore found an application in the visualization of short-duration, hypersonic flow-fields through the work of Kirmse et al 12 A laser speckle pattern generated by the background illumination of ground glass was used as a background pattern to visualize the shock layer of a 160mm diameter sphere in flows of M = 8.1 with total enthalpies ranging from 12MJ/kg to 22MJ/kg. Although satisfactory agreement with computational work was obtained, due to the ungovernable shape and size of particulates, a printed background is posturized to improve system sensitivity and reliability.…”

“…A variety of qualitative background generation techniques have been used in literature, from splashing tiny droplets of paint with a brush 21 to laser speckles generated through ground glass. 12 The subsequent quantitative approach to the background grid generation is discussed below.…”

“…[8][9][10] The BOS method has been used to visualize large field-of-view flows in applications ranging from on-site industrial HVAC systems to short-duration shock tunnel facilities. [11][12][13][14] Reinholtz et al utilized a pseudo-random pattern of manually stamped 3/16" black dots on retro-reflective paint in the AEDC's 16-ft transonic tunnel. 11 The constant diameter dot sizing corresponded to 3-5 pixel diameter dots when imaged allowing for sub pixel accuracy, while variable density gradient magnitudes in separate regions of the flow required a variation in interrogation window sizing.…”

Background-oriented schlieren (BOS) techniques

“…Ramanah and Mee (2006) and Ramanah et al (2007), for example, investigated scramjet flows in hypersonic impulse facility and compared the results with conventional schlieren images. Kirmse et al (2011) performed combined PIV and BOS measurements in a highenthalpy shock tunnel at Mach 8. Supersonic facilities such as shock tubes have also been used in order to visualize the shock-heated regions on a sharp cone at Mach 3.8 (Raghunath et al 2004) and shock waves at Mach 4 (Mizukaki 2010).…”

“…The latter used a Movistrob 400 (Bamberg and Bormann Electronic Gmbh) with a maximum light intensity of 550 lux and a pulse width of about 8 µs. Kirmse et al (2011) used an Nd:YAG laser generating pulses of 25 ns in combination with optical band path filters in front of the camera in order to minimize the influence of the self-luminosity of the highenthalpy flow under investigation. Yamamoto et al (2014) utilized a laser stroboscope with a pulse width of 20 ns as an illumination source (CAVITAR, Finland).…”