Particle Image Velocimetry Measurements of the Separation Bubble on an Iced Airfoil

Jacobs, Jason; Bragg, Michael B.

doi:10.2514/6.2006-3646

Cited by 13 publications

(27 citation statements)

References 15 publications

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“…The main separated bubble length increases with the angle-of-attack but the smaller bubble trapped between the glaze-ice and a little accreted ice behind the main ice and do not change significantly with increasing the angle-of-attack. These phenomenon has been predicted in previous works for NACA0012 [9,10] and for backward-facing step flow investigated by Kostas et al [13], and Hudy et al [8]. On the lower surface of the airfoil the same pattern is detected.…”

Section: Resultssupporting

confidence: 72%

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Numerical and experimental study of flow field characteristics of an iced airfoil

Mirzaei

Ardekani

Doosttalab

2009

Aerospace Science and Technology

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Section: Resultssupporting

confidence: 72%

“…In this study Bragg method [9] was employed for estimation of reattachment points for both CFD and experimental simulations. Fig.…”

Section: Resultsmentioning

confidence: 99%

Numerical and experimental study of flow field characteristics of an iced airfoil

Mirzaei

Ardekani

Doosttalab

2009

Aerospace Science and Technology

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“…In the latter experiments two-and three-dimensional castings were used in order to reproduce the ice accretions. Even though the spanwise modulation is much more apparent when the three-dimensional castings were used, it is also present with two-dimensional casting; Jacobs & Bragg (2006) suggested that the observed three-dimensionality may be a demonstration of the existence of a global mode in the separation bubble.…”

Section: Summary and Discussionmentioning

confidence: 94%

“…The perturbed separation and reattachment lines are described by a set of connected no-slip (node and saddle) critical points on the wall surface, as seen in figure 9(a, b). Identical topologies have been observed experimentally in separation bubbles on a flat plate (Perry & Fairlie 1975), either by oil-visualization techniques or by particle image velocimetry on iced airfoils (Gurbacki 2003;Jacobs & Bragg 2006). In the latter experiments two-and three-dimensional castings were used in order to reproduce the ice accretions.…”

Section: Summary and Discussionmentioning

confidence: 99%

Structural changes of laminar separation bubbles induced by global linear instability

Rodríguez

Theofilis

2010

J. Fluid Mech.

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The topology of the composite flow fields reconstructed by linear superposition of a two-dimensional boundary layer flow with an embedded laminar separation bubble and its leading three-dimensional global eigenmodes has been studied. According to critical point theory, the basic flow is structurally unstable; it is shown that in the presence of three-dimensional disturbances the degenerate basic flow topology is replaced by a fully three-dimensional pattern, regardless of the amplitude of the superposed linear perturbations. Attention has been focused on the leading stationary eigenmode of the laminar separation bubble discovered by Theofilis et al. (Phil. Trans. R. Soc. Lond. A, vol. 358, 2000, pp. 3229-3324); the composite flow fields have been fully characterized with respect to the generation and evolution of their critical points. The stationary global mode is shown to give rise to a three-dimensional flow field which is equivalent to the classical U-shaped separation, defined by Hornung & Perry (Z. Flugwiss. Weltraumforsch., vol. 8, 1984, pp. 77-87), and induces topologies on the surface streamlines that are resemblant to the characteristic stall cells observed experimentally. IntroductionThe instability of a laminar separation bubble (LSB), embedded inside a boundary layer and arising as a consequence of an adverse free-stream pressure gradient on a flat surface, or induced by changes of the surface curvature, constitutes a problem of prime technological significance: in an aeronautical context related applications include lifting surfaces, low-pressure turbines and wind-turbine blades. The presence of a separated shear layer as an integral part of the LSB suggests that the instability properties of the shear layer should play a decisive role in the reattachment of the separated boundary layer. The one-dimensionality of the model shear-layer profile and its resulting amenability to classic, ordinary-differential-equation-based analysis (Michalke 1964; Blumen 1970 and subsequent work in this 'local' vein) has generated a wealth of knowledge on the problem of shear-layer instability perse and as applied to the LSB flow. On the other hand, Gaster postulated (H. Fasel, private communication November 2004) that, besides paying attention to the amplification of incoming disturbances by solution of the local instability problem, analysis of LSB flows 'in the true sense' should also be performed, by which a global instability analysis of the entire separated boundary layer flow is implied.

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“…The behaviour of large-scale vortex shedding and the differences in the iced-aerofoil flowfields between a three-dimensional ice shape casting and a two-dimensional extrusion of the ice shape casting were identified by Jacobs and Bragg (5,6) . From this investigation, it was discovered that the three-dimensional horn-ice shape produced stream-wise vortex structures, which led to a faster pressure recovery of the separated boundary layer, and thus a shorter mean reattachment length than the two-dimensional extrusion of the ice shape.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of flowfield over an iced aerofoil

Manshadi¹,

Esfeh

2016

Aeronaut. j.

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Wind-tunnel measurements were used to study the characteristics of the unsteady separation bubbles on a NACA 0015 aerofoil with simulated two-dimensional leading-edge glaze ice accretions. The unsteadiness present in the iced-aerofoil flowfield was determined using measurements of the time-dependent aerofoil surface pressure distribution at Reynolds number of 1.0 × 106. Additionally, the unsteady flow features were investigated through the power spectrum of the stream-wise velocity fluctuations using a hot-wire anemometry. The results showed that the highest value of root-mean-square fluctuation of the surface pressure consistently occurred upstream of the mean shear-layer reattachment location. Spectral analysis of stream-wise velocity fluctuations near reattachment location revealed evidence of the regular frequency at Strouhal numbers of 0.5-0.63. Moreover, the low-frequency oscillations associated with shear-layer flapping was also identified in the wake velocity spectra on the order of 10 Hz that resulted in Strouhal numbers of 0.0186-021.

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Particle Image Velocimetry Measurements of the Separation Bubble on an Iced Airfoil

Cited by 13 publications

References 15 publications

Numerical and experimental study of flow field characteristics of an iced airfoil

Numerical and experimental study of flow field characteristics of an iced airfoil

Structural changes of laminar separation bubbles induced by global linear instability

Experimental investigation of flowfield over an iced aerofoil

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