The Effect of the Mach Number on a Turbulent Backward-Facing Step Flow

Bolgar, Istvan; Scharnowski, Sven; Kähler, Christian J.

doi:10.1007/s10494-018-9921-7

Cited by 26 publications

(27 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1. The facility is discussed in detail in Bolgar et al (2018). Two adjustable throats, the Laval nozzle upstream of the test section and the diffuser further downstream, enable an operating range of Mach numbers from 0.2 to 3.0.…”

Section: Measurement Setupmentioning

confidence: 99%

Accurate turbulence level estimations using PIV/PTV

2018

Self Cite

View full text Add to dashboard Cite

The estimation of the turbulence level of flow facilities is very important for the comprehensive description of experimental results. While for low flow velocities various measurement techniques can be used (for example hot-wire, LDV, PIV) the task becomes difficult in the case of compressible flows as temperature and density fluctuations bias the measurement of the velocity fluctuations. In this work, we analyze the free-stream flow of the trisonic wind tunnel Munich (TWM) by means of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The goal is to determine the flow quality, i.e. the turbulence level, over the operating range of the facility without bias due to temperature and density variations. The capability of PIV/PTV for the estimation of small velocity fluctuations is investigated in detail. It is shown that a small particle shift on the measurement plane in combination with a large particle image displacement on the image plane allows for precise velocity measurements. Furthermore, a variation of the time separation between the PIV double images, t , enables the measurement uncertainty to be determined, which was estimated to be as low as 0.04% of the mean displacement for a mean displacement of x = 100 pixel and an interrogation window size of 32 × 32 pixel. Regarding the wind tunnel turbulence, it was found that the turbulence level generally decreases with increasing Mach number for the TWM facility, starting with 1.9% at Ma = 0.3 and reaching 0.45% at Ma = 3.0 . With this analysis, a methodology exists to perform accurate turbulence measurements in incompressible and compressible flows.

show abstract

Section: Measurement Setupmentioning

confidence: 99%

Accurate turbulence level estimations using PIV/PTV

2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…Due to the small number of particle images, the mean reattachment length for the supersonic cases could not be reliably determined and is, therefore, not indicated. For the subsonic cases without nozzle flow, the reattachment length (normalized with the step height) is about 10% − −15% shorter compared to the measurements in [8], which were performed on a model with longer splitter plate and without nozzle. On the other hand, numerical simulations of a planar launcher model with dual-bell nozzle in sea-level mode performed by [24] predict a 20% longer reattachment length for M = 0.8 .…”

Section: Velocity Measurementsmentioning

confidence: 77%

“…Additionally, only a 2D model allows for symmetric inflow conditions for the outer flow and the nozzle flow. Experiments with the same forebody geometry confirmed the two-dimensionality and characterized the boundary layer at the end of the main body [6,8,35]. Axisymmetric models are usually mounted by means of struts [15,31,42] which might disturb the outer flow.…”

Section: Measurement Set-upmentioning

confidence: 80%

“…Only very few particles could be detected within the recirculation region of the step. This indicates that only the largest particles could be seen with the chosen laser and camera set-up, because in earlier works, much more seeding was present in this region [8,35]. For the densely seeded PIV images, a background noise level with a standard deviation ≈ 6.8 counts was estimated from the auto-correlation function with the method presented in [32].…”

Section: Velocity Measurementsmentioning

confidence: 93%

“…The thickness of the forebody and the splitter plate is 25 mm and 15 mm, respectively. The forebody geometry is the same as that used in [8,35,47]. In the center of the splitter plate, a 2D dual-bell nozzle is integrated.…”

Section: Measurement Set-upmentioning

confidence: 99%

See 2 more Smart Citations

Investigation of the base flow of a generic space launcher with dual-bell nozzle

Scharnowski

Kähler

2020

CEAS Space J

Self Cite

View full text Add to dashboard Cite

The typical afterbody flow of a space launcher is characterized by a strong interaction of the engine’s exhaust jet and the separated shear layer emerging from the main body. This interaction is further complicated by strong changes in the spatial and temporal behavior of the afterbody flow during the atmospheric ascent of a launcher. Theoretically, a dual-bell nozzle not only allows for a gain in payload compared to standard single-bell nozzles, but also it alters the wake flow topology due to the two nozzle modes. To predict the benefits as well as the additional risks, the afterbody flow of a generic space launcher model equipped with a cold-flow dual-bell nozzle is investigated in detail. The flow was analyzed for sub-, trans- and supersonic Mach numbers ranging from 0.3 to 2.9 for a variety of nozzle pressure ratios. Particle image velocimetry measurements and schlieren measurements with high repetition rate were performed to determine the dynamics of the separated shear layer, the nozzle jet and their interaction. It is shown that the reattachment length of the base flow decreases with increasing nozzle pressure ratio. Furthermore, the nozzle pressure ratio at which the dual-bell nozzle switches from sea-level mode to altitude mode is reduced by $$15\%$$ 15 % with high subsonic outer flow and by as much as $$65\%$$ 65 % for an outer flow at a Mach number of 1.6. Even for a constant nozzle pressure ratio, the nozzle flow topology depends on the Mach number of the outer flow.

show abstract