Fluctuating pressure measurements in a turbulent separation bubble

Trünkle, Julian; Mohammed-Taifour, Abdelouahab; Weiss, Julien

doi:10.1016/j.crme.2015.09.003

Cited by 6 publications

(4 citation statements)

References 13 publications

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“…This indicates that the flow was generally unsteady and three-dimensional. In Figure 1.10c, it can be seen that similar surface flow patterns were observed by Barone et al 16 In that study, separation on a smooth surface due to adverse pressure gradients was observed, at comparable Reynolds numbers to the present study. Separation was found to be highly unsteady, which again is consistent with these results.…”

Section: Surface Flow Visualization Resultssupporting

confidence: 74%

“…Of particular interest are the irregular separation lines, similar to those observed in Trünkle et al 16 The The results of the simple inviscid flowfield (Fig. 3.6) show that decreasing the width of the scavenge channel results in lower pressures and higher velocities, as expected.…”

Section: A Surface Flow Visualization Resultssupporting

confidence: 63%

“…Surface flow visualization is used to characterize the large scale flow structures and separation 16 . The tests were conducted with titanium dioxide as the colorant, kerosene as the carrier fluid, and oleic acid as an emulsifier.…”

Section: F Surface Flow Visualizationmentioning

confidence: 99%

“…Surface flow visualization is used to characterize the large scale flow structures and separation 16 . …”

Section: Surface Flow Visualizationmentioning

confidence: 99%

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A Parametric Study of Inertial Particle Separator Geometry

Connolly¹

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An Inertial Particle Separator (IPS) is a particulate removal device typically installed at the inlet of a gas turbine to mitigate effects of sand ingestion on the engine. This system can minimize particulate ingestion during helicopter landings in austere brown-out conditions so as to increase engine life. Typically, IPS systems have lower engine power losses than alternative engine inlet filtration technologies.The present studies investigated a variety of novel IPS geometries. Tests were conducted on a fundamental twodimensional experimental facility that allows optical access. Geometries were evaluated using a variety of performance criteria. Of primary import is particle separation efficiency which measures the effectiveness of the system at removing particulate from the core engine flow stream. The separation efficiency of a particular IPS configuration is reliant in part on the characteristics of the flowfield, especially for finer particulate. Low scavenge air mass flow fractions are desirable, as it is directly related to the amount of power diverted from the engine to power the IPS. However, lowering scavenge mass flow fraction increases rates of flow separation and instability, leading to lost particle separation efficiency. There is a lack of available experimental data for IPS geometries designed to operate effectively at these low scavenge mass flow fractions.Modifications from a baseline geometry were made to the scavenge leg and Outer Surface Geometry (OSG).Performance was evaluated based on particle separation efficiency, Particle Image Velocimetry (PIV), surface flow visualization, first order predictive methods, as well as power loss and mass flow rate variations. These experiments showed that reductions in the scavenge channel height were effective at increasing separation efficiency at low scavenge mass flow fraction. Additionally, these modifications successfully reduced flow instability and demonstrated a link between flow separation and particle separation efficiency. The present studies provide comprehensive empirical data to guide future development of IPS geometries specifically optimized to perform effectively at low power levels.4

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Section: Surface Flow Visualization Resultssupporting

confidence: 74%

Section: A Surface Flow Visualization Resultssupporting

confidence: 63%

Section: F Surface Flow Visualizationmentioning

confidence: 99%

“…Surface flow visualization is used to characterize the large scale flow structures and separation 16 . …”

Section: Surface Flow Visualizationmentioning

confidence: 99%

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A Parametric Study of Inertial Particle Separator Geometry

Connolly¹

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Unsteadiness in a large turbulent separation bubble

Mohammed-Taifour

Weiss

2016

J. Fluid Mech.

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The unsteady behaviour of a massively separated, pressure-induced turbulent separation bubble (TSB) is investigated experimentally using high-speed particle image velocimetry (PIV) and piezo-resistive pressure sensors. The TSB is generated on a flat test surface by a combination of adverse and favourable pressure gradients. The Reynolds number based on the momentum thickness of the incoming boundary layer is 5000 and the free stream velocity is$25~\text{m}~\text{s}^{-1}$. The proper orthogonal decomposition (POD) is used to separate the different unsteady modes in the flow. The first POD mode contains approximately 30 % of the total kinetic energy and is shown to describe a low-frequency contraction and expansion, called ‘breathing’, of the TSB. This breathing is responsible for a variation in TSB size of approximately 90 % of its average length. It also generates low-frequency wall-pressure fluctuations that are mainly felt upstream of the mean detachment and downstream of the mean reattachment. A medium-frequency unsteadiness, which is linked to the convection of large-scale vortices in the shear layer bounding the recirculation zone and their shedding downstream of the TSB, is also observed. When scaled with the vorticity thickness of the shear layer and the convection velocity of the structures, this medium frequency is very close to the characteristic frequency of vortices convected in turbulent mixing layers. The streamwise position of maximum vertical turbulence intensity generated by the convected structures is located downstream of the mean reattachment line and corresponds to the position of maximum wall-pressure fluctuations.

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