Measurements with a flow direction boundary-layer probe in a two-dimensional laminar separation bubble

Häggmark, C. P.; Bakchinov, Andrey; Alfredsson, P. Henrik

doi:10.1007/s003480050383

Cited by 12 publications

(7 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[6][7][8][9][10] Laminar separated flows that develop due to the application of an adverse pressure gradient are inherently unstable. [6][7][8][9][10] Laminar separated flows that develop due to the application of an adverse pressure gradient are inherently unstable.…”

Section: Introductionmentioning

confidence: 99%

Coherent structures in an airfoil boundary layer and wake at low Reynolds numbers

2006

View full text Add to dashboard Cite

Mitigation of preferential concentration of small inertial particles in stationary isotropic turbulence using electrical and gravitational body forces Phys. Fluids 24, 073301 (2012) Axisymmetric intrusions in two-layer and uniformly stratified environments with and without rotation Phys. Fluids 24, 036603 (2012) Wavelet decomposition of forced turbulence: Applicability of the iterative Donoho-Johnstone threshold Phys. Fluids 24, 025102 (2012) Maximizing dissipation in a turbulent shear flow by optimal control of its initial state Phys. Fluids 23, 045105 (2011) A stochastic model of coherent structures for particle deposition in turbulent flows Phys. Fluids 20, 053303 (2008) Additional information on Phys. Fluids Boundary layer and turbulent wake development for a NACA 0025 airfoil at low Reynolds numbers was studied experimentally. Wind tunnel experiments were carried out for a range of Reynolds numbers and three angles of attack. Laminar boundary layer separation occurs on the upper surface of the airfoil for all Reynolds numbers and angles of attack examined. Two flow regimes are investigated ͑i͒ boundary layer separation without reattachment and ͑ii͒ separation bubble formation. The results suggest that coherent structures form in the separated flow region and the wake of the airfoil for both flow regimes. The formation of the roll-up vortices in the separated shear layer is linked to inviscid spatial growth of disturbances and is attributed to the Kelvin-Helmholtz instability. Linear stability theory can be employed to adequately describe the salient characteristics of such vortices and the initial stage of the separated shear layer transition. The development of the roll-up vortices leads to boundary layer transition, and the vortices break down during the transition process. Vortex shedding also occurs in the airfoil wake and vortices form in the near-wake region. It is shown that the boundary layer behavior has a profound effect on the identified coherent structures, and each of the two flow regimes is associated with distinctly different vortex shedding characteristics.

show abstract

Section: Introductionmentioning

confidence: 99%

Coherent structures in an airfoil boundary layer and wake at low Reynolds numbers

2006

View full text Add to dashboard Cite

show abstract

“…They also presented an analysis algorithm for utilizing the skewness of hot-film signals for detecting the transition on a pitching airfoil. 3 H€ aggmark et al 4 carried out measurements with a directional sensitive hot-wire probe in a 2D LSB caused by an adverse pressure gradient. The reversed flow occurrence and the intermittency were recorded inside the bubble.…”

Section: Introductionmentioning

confidence: 99%

Investigation of laminar separation bubble over a supercritical airfoil in an incompressible flow

Tatar

Masdari

Tahani

2021

Proceedings of the Institution of Mechanical Engineers, Part C:

View full text Add to dashboard Cite

Supercritical airfoils have an unknown behavior at incompressible flow regime and Reynolds numbers lower than those related to their design point at transonic condition. In this work, boundary layer transition is studied over a supercritical airfoil by means of hot-film and pressure measurements completed with numerical simulations. The experiments are performed at chord-based Reynolds number of [Formula: see text]and Mach number of [Formula: see text] at different angles of attack. Hot-film measurement over the upper surface of the supercritical airfoil is carried out and the transition points are computed using the standard deviation of the signals. The upper surface pressure is also recorded and a peak in its second derivative is presented as the transition point generated by the laminar separation bubble mechanism. Moreover, an appropriate time-frequency analysis is applied to the hot-film signals to get an insight into the spectral content and development of the transitional boundary layer structures. On the other hand, two numerical codes are employed and the transition points obtained from numerical simulations are compared with the experimental outcomes. Results express a rapid change of the bubble position over the upper surface, as the angle of attack is increased to the value of [Formula: see text]. Laminar separation bubble is observed in the surface pressure distribution data and is well identified using its second derivative along the streamwise direction. The spectral characteristics of the boundary layer are satisfactorily explored including the streamwise fluctuations within the laminar flow, intermittent behavior of the transitional zone and the wide range of the spectrum in turbulent flow, thanks to the time-frequency analysis. A promising agreement is observed between the transition points computed by both the numerical and experimental studies and confirms the accuracy of findings achieved by the second derivative of surface pressure data, hot-film measurements and the reliability of the employed numerical transition models for optimization studies.

show abstract

“…The flow in the cavity is spouted again, achieving small fine injections through numerous small porous holes. In order to figure out the effect of the jets on the flow field experimentally in the cavity, the relatively high response device for measuring the flow direction, so called thermal tuft probe reported by C. P. Häggmark, et al [8], is applied in the cavity instead of using conventional tuft. To reveal the flow field, it is necessary to investigate the flow direction in the cavity.…”

Section: Introductionmentioning

confidence: 99%

Study of Interaction between Supersonic Flow and Rods or Jets Surrounded by Porous Cavity

Kuniyoshi¹,

Yaga²,

Koda³

et al. 2012

OJFD

View full text Add to dashboard Cite

In this experiment, the effects of the combination of jets or rods and a porous cavity on the supersonic flow field are studied by means of visualization of schlieren method and the measurements of wall static pressures and the flow direction in the cavity with the thermal tuft probe. Three cases of jets or rods arrangements are tested in the experiments. As a result, a bow shock wave which is generated by the jets or rods is observed by mean of schlieren method. And it is confirmed that the expansion region appears downstream of the rods but is not in case of the jets pattern. Moreover the pressure ratios of starting shock wave passing through porous cavity for jets pattern differ from that of rods pattern. In the cavity, the flow direction at the measurement position in the cavity is always opposite to the main flow, as long as the starting shock wave is located upstream of the porous cavity for all cases. Difference in the backward flow ratio between the jets and rods patterns is observe after the starting shock wave passes through the porous cavity.

show abstract

Measurements with a flow direction boundary-layer probe in a two-dimensional laminar separation bubble

Cited by 12 publications

References 6 publications

Coherent structures in an airfoil boundary layer and wake at low Reynolds numbers

Coherent structures in an airfoil boundary layer and wake at low Reynolds numbers

Investigation of laminar separation bubble over a supercritical airfoil in an incompressible flow

Study of Interaction between Supersonic Flow and Rods or Jets Surrounded by Porous Cavity

Contact Info

Product

Resources

About