A new wind tunnel for the study of pressure-induced separating and reattaching flows

Mohammed-Taifour, Abdelouahab; Schwaab, Quentin; Pioton, J.; Weiss, Julien

doi:10.1017/s0001924000010265

Cited by 19 publications

(23 citation statements)

References 33 publications

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“…At this velocity, the Reynolds number based on the boundary-layer momentum thickness is Re θ ≃ 5000 upstream of separation (x 1.10 m). It was verified by Mohammed-Taifour et al [30] that the incoming boundary layer has the characteristics of a "canonical" ZPG boundary layer. Across the span of the test section, the integral thicknesses of the incoming boundary layer are constant within 5% and the friction coefficient within 7%.…”

Section: A Wind Tunnelmentioning

confidence: 87%

“…Given that the most energetic frequency of flow fluctuations in the separated region is less than 100 Hz, no software correction was applied to the anemometer's signal. The overall accuracy of the longitudinal velocity measurements was estimated to be about 1% at the 95% confidence level [30].…”

Section: B Instrumentationmentioning

confidence: 96%

“…The experiments reported in this paper were performed in the TFT Boundary-Layer Wind Tunnel, which was specifically designed and constructed for this purpose [30]. The wind tunnel features a 3-meterlong test section designed to produce a zero-pressure-gradient (ZPG) turbulent boundary layer in its first half.…”

Section: A Wind Tunnelmentioning

confidence: 99%

“…This combination creates a massively separated, closed separation bubble on the test surface. A detailed description of the wind-tunnel geometry, the distribution of the pressure coefficient in the complete test section, and an interpretation of oil-film visualization experiments are provided in Mohammed-Taifour et al [30]. Figure 1 shows a sketch of the test section in the region of the separation bubble.…”

Section: A Wind Tunnelmentioning

confidence: 99%

“…The forward-flow fraction γ is defined as the percentage of the time that the flow moves in the main (downstream) direction. The design and testing of the thermal tuft was reported in Schwaab and Weiss [32], and the first experimental results in the TFT Boundary-Layer Wind Tunnel are provided in Mohammed-Taifour et al [30]. The probe's uncertainty was estimated at 1.5% at the 95% confidence level [32].…”

Section: B Instrumentationmentioning

confidence: 99%

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Unsteady Behavior of a Pressure-Induced Turbulent Separation Bubble

2015

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Wall static-pressure and longitudinal-velocity fluctuations are measured in a pressure-induced turbulent separation bubble generated on a flat test surface by a combination of adverse and favorable pressure gradients. The Reynolds number, based on momentum thickness upstream of separation, is Re θ ≃ 5000 at a free-stream velocity of U ref 25 m∕s. The results indicate that the flow is characterized by two separate time-dependent phenomena: a lowfrequency mode, with a Strouhal number St 1 ≃ 0.01, which is related to a global "breathing" motion (i.e., contraction/ expansion) of the separation bubble, and a higher-frequency mode, with a Strouhal number St 2 ≃ 0.35, which is linked to the roll-up of vortical structures in the shear layer above the recirculating region and their shedding downstream of the bubble. These two phenomena are reminiscent of the "flapping" and "shedding" modes observed in fixed-separation experiments, though their normalized frequencies are different. The breathing mode is also shown to be strikingly similar to the low-frequency unsteadiness observed in shock-induced separated flows at supersonic speeds. Nomenclaturepower spectrum of movable sensor G xx = measured power spectrum of reference (fixed) sensor G yy = measured power spectrum of movable sensor h = maximum height of dividing streamline L = length scale in shock-induced separated flows L b = length of separation bubble, which is equal to 0.42 m p = static pressure p 0 = fluctuating static pressure Re θ = Reynolds number based on momentum thickness St, St 1;2 = Strouhal number, which is equal to fL b ∕U ref St f , St s = Strouhal number of flapping and shedding modes, which is equal to fx R ∕U ∞ St L = Strouhal number in shock-induced separated flows, which is equal to fL∕U ∞ St δ ω = Strouhal number of free shear layers, which is equal to fδ ω ∕ U T C = time constant of constant-voltage anemometer circuit Tu = turbulence level U = longitudinal velocity U = average velocity in the shear layer, which is equal to U max ∕2 U c = convective velocity U s = mean longitudinal velocity of inviscid flow at separation V w = voltage across hot-wire probe x = longitudinal position in test section x R = length scale in fixed-separation flows x det = longitudinal position of transitory detachment on test-section centerline, which is equal to 1.75 m x = nondimensional longitudinal position in test section, which is equal to x − x det ∕L b x D = short-time average of nondimensional instantaneous detachment position x R = short-time average of nondimensional instantaneous reattachment position y = vertical position under test surface, positive going down z = spanwise position in test section δ = 99% boundary-layer thickness δ ω = shear-layer vorticity thickness, which is equal to U max − U min ∕∂U∕∂y max γ = forward-flow fraction γ 0 = short-time average of forward-flow fraction ν = kinematic viscosity θ = momentum thickness ρ = air density Subscripts ref = measurement at wind-tunnel reference location (center of contraction exit area) rms = root mean...

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Section: A Wind Tunnelmentioning

confidence: 87%

Section: B Instrumentationmentioning

confidence: 96%

Section: A Wind Tunnelmentioning

confidence: 99%

Section: A Wind Tunnelmentioning

confidence: 99%

Section: B Instrumentationmentioning

confidence: 99%

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Unsteady Behavior of a Pressure-Induced Turbulent Separation Bubble

2015

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A detailed procedure for measuring turbulent velocity fluctuations using constant-voltage anemometry

et al. 2015

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Calorimetric wall-shear-stress microsensors for low-speed aerodynamics

Weiss,

Giani

2024

Exp Fluids

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This article describes the design, calibration, and testing of new calorimetric microsensors for the measurement of wall shear stress in low-speed aerodynamic flows. The sensors are made of three beams of platinum-plated silicon nitride suspended over a small cavity. Their range of operation and their bandwidth are of the order of $$\pm 10$$ ± 10 Pa and 1 kHz, respectively. Results from experimental campaigns in a laminar separation bubble, a turbulent separation bubble, and on a NACA 0015 airfoil at low Reynolds number indicate a high sensitivity and an inherent capacity to measure instantaneous backflow. This demonstrates the capability of the new sensors to accurately determine the mean and fluctuating wall shear stress in laminar, transitional, and turbulent separating and reattaching flows.

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A new wind tunnel for the study of pressure-induced separating and reattaching flows

Cited by 19 publications

References 33 publications

Unsteady Behavior of a Pressure-Induced Turbulent Separation Bubble

Unsteady Behavior of a Pressure-Induced Turbulent Separation Bubble

A detailed procedure for measuring turbulent velocity fluctuations using constant-voltage anemometry

Calorimetric wall-shear-stress microsensors for low-speed aerodynamics

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