Mechanism of entrainment in turbulent wakes

Bevilaqua, Paul M.; Lykoudis, Paul S.

doi:10.2514/3.6414

Cited by 28 publications

(10 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Clearly, the wake width determined by y 0.95 is narrower than those in terms of flatness factor and shear-induced vorticity. This fact corroborates with what were experimentally observed [1][2][3] that the phenomenon of intermittency in the outer region of the wake width, defined by l u , can be still observed. …”

Section: Resultssupporting

confidence: 80%

See 1 more Smart Citation

Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder

Shih

Chen

Chang

et al. 2016

Int. J. Mod. Phys. Conf. Ser.

View full text Add to dashboard Cite

There are two general concerns in the velocity measurements of turbulence. One is the temporal characteristics which governs the turbulent mixing process. Turbulence is rotational and is characterized by high levels of fluctuating vorticity. In order to obtain the information of vorticity dynamics, the spatial characteristics is the other concern. These varying needs can be satisfied by using a variety of diagnostic techniques such as invasive physical probes and non-invasive optical instruments. Probe techniques for the turbulent measurements are inherently simple and less expensive than optical methods. However, the presence of a physical probe may alter the flow field, and velocity measurements usually become questionable when probing recirculation zones. The non-invasive optical methods are mostly made of the foreign particles (or seeding) instead of the fluid flow and are, thus, of indirect method. The difference between the velocities of fluid and foreign particles is always an issue to be discussed particularly in the measurements of complicated turbulent flows. Velocity measurements of the turbulent wake flow over a circular cylinder will be made by using two invasive instruments, namely, a cross-type hot-wire anemometry (HWA) and a split-fiber hot-film anemometry (HFA), and a non-invasive optical instrument, namely, particle image velocimetry (PIV) in this study. Comparison results show that all three employed diagnostic techniques yield similar measurements in the mean velocity while somewhat deviated results in the root-mean-squared velocity, particularly for the PIV measurements. It is demonstrated that HFA possesses more capability than HWA in the flow measurements of wake flow. Wake width is determined in terms of either the flatness factor or This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 3.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited.

show abstract

Section: Resultssupporting

confidence: 80%

“…Here U ∞ and U c are the mean stream-wise velocities in the free stream and at the centerline, respectively. However, it is argued [1][2][3] that the phenomenon of intermittency, which is an evidence of turbulent fluctuations, in the outer region of the wake width, …”

Section: Introductionmentioning

confidence: 99%

Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder

Shih

Chen

Chang

et al. 2016

Int. J. Mod. Phys. Conf. Ser.

View full text Add to dashboard Cite

show abstract

“…Bevilaqua & Lykoudis 1971;Brown & Roshko 1974). The assertion here is that entrainment usually also involves a large-scale process sometimes called engulfment, or gulping, in which non-turbulent fluid is incorporated into the turbulence by a folding process analogous to the rolling-up of a rug.…”

Section: Entrainmentmentioning

confidence: 99%

Structure and entrainment in the plane of symmetry of a turbulent spot

1978

View full text Add to dashboard Cite

641Laser-Doppler velocity measurements in water are reported for the flow in the plane of symmetry of a turbulent spot. The unsteady mean flow, defined as an ensemble average, is fitted to a conical growth law by using data at three streamwise stations to determine the virtual origin in x and t. The two-dimensional unsteady stream function is expressed as 1fr = U~ tg(£, r/) in conical similarity co-ordinates g = xfUoot and 1J = y jU 00 t. In these co-ordinates, the equations for the unsteady particle displacements reduce to an autonomous system. This system is integrated graphically to obtain particle trajectories in invariant form. Strong entrainment is found to occur along the outer part of the rear interface and also in front of the spot near the wall. The outer part of the forward interface is passive. In terms of particle trajectories in conical co-ordinates, the main vortex in the spot appears as a stable focus with celerity 0· 77U 00 • A second stable focus with celerity 0·64U 00 also appears near the wall at the rear of the spot.Some results obtained by flow visualization with a dense, nearly opaque suspension of aluminium flakes are also reported. Photographs of the sublayer flow viewed through a glass wall show the expected longitudinal streaks. These are tentatively interpreted as longitudinal vortices caused by an instability of Taylor-Gortler type in the sublayer.

show abstract

“…Here, the term engulfing refers to the motion of ambient fluid into the region of the wake. Bevilaqua & Lykoudis (1971), based on experiments on the near wake of a sphere, observe that entrainment occurs in three phases: ambient fluid first deforms as the bounding interface approaches, it is then swirled into the wake by the spinning motion of large vortices associated with surface waves and turbulent mixing occurs in the final phase of entrainment. The rotation of the large vortices is the principal mechanism of wake growth.…”

Section: Introductionmentioning

confidence: 99%

Detached shear-layer instability and entrainment in the wake of a flat plate with turbulent separating boundary layers

Mohan

2015

J. Fluid Mech.

View full text Add to dashboard Cite

The near and very near wake of a flat plate with a circular trailing edge, with vigorous vortex shedding, is investigated with data from direct numerical simulations (DNS). Computations were performed for four different combinations of the Reynolds numbers based on plate thickness (D) and momentum thickness near the trailing edge (θ ). Unlike the case of the cylinder, these Reynolds numbers are independent parameters for the flat plate. The objectives of the study are twofold, to investigate the entrainment process when the separating boundary layers are turbulent and to better understand the instability of the detached shear layers (DSLs). A visualization of the entrainment process, the effect of changing the ratio θ /D on entrainment and wake-velocity statistics, and a way of understanding entrainment in a phase-averaged sense via distributions of the turbulent transport rate are provided here. The discussion on shear-layer instability focuses on the role of log-layer eddies in the destabilization process, the effect of high-speed streaks in the turbulent boundary layer in the vicinity of the trailing edge on shear-layer vortex generation rates, and a relationship between the prevalence of shear-layer vortex generation and shedding phase that is a result of an interaction between the shedding process and the shear-layer instability mechanism. A power-law relationship between the ratio of shear-layer and shedding frequencies and the Reynolds numbers mentioned above is obtained. A discussion of the relative magnitudes of the exponents is provided. A second power-law relationship between shed-vortex strength and these two Reynolds numbers is also proposed.

show abstract

Mechanism of entrainment in turbulent wakes

Cited by 28 publications

References 4 publications

Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder

Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder

Structure and entrainment in the plane of symmetry of a turbulent spot

Detached shear-layer instability and entrainment in the wake of a flat plate with turbulent separating boundary layers

Contact Info

Product

Resources

About