Experimental investigation on the effect of particles on large scale vortices of an isolated hemispherical roughness element

Gao, Tiehong; Sun, Jinhua; Chen, Wenyi; Fan, Ying; Zhang, Yan-tao

doi:10.1063/5.0050773

Cited by 9 publications

(7 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the central plane of the MHVs (y/R = 0), negative Reynolds stress (blue contours) in the area of the MHV head portion indicates strong ejection and sweeping(Corino & Brodkey 1969) momentum transport between the outer flow and the near wall flow. Positive Reynolds stress (red contours) exists obliquely below the negative Reynolds stress area, which is similar to the observation ofGao et al (2021). Recall in figure6, the velocity profile exhibits a 'concave' shape in the range 0.4 < z/R < 1 due to the velocity deficit in the near wake.…”

supporting

confidence: 84%

“…There have been many studies performed on hemispherical roughness elements (Toy et al 1983;Tang & Jiang 2012;Citro et al 2015), especially within turbulent boundary layers (Savory & Toy 1986b;Manhart 1998;Tavakol & Yaghoubi 2010;Tavakol, Yaghoubi & Motlagh 2010;Guala et al 2012;Wood et al 2016;Cao & Tamura 2020;Li et al 2022). Previous investigations also include particle transport in hemispherical wakes (Prevel et al 2013;Gao et al 2021), hemisphere in pulsatile flows (Carr & Plesniak 2016;Carr et al 2020), and hemispherical wakes in the supersonic regime (Wang et al 2012;Mortazavi et al 2014;Kiriakos et al 2021). Large-eddy simulations (LES) and direct numerical simulations (DNS) have been applied widely in the above-mentioned studies.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tomographic PIV investigation on near-wake structures of a hemisphere immersed in a laminar boundary layer

Tu,

Wang,

Gao

et al. 2023

J. Fluid Mech.

View full text Add to dashboard Cite

The near wake of a hemisphere immersed in a laminar boundary layer is studied utilizing time-resolved tomographic particle image velocimetry (TPIV). Focus is placed on the three-dimensional vortical structures and the formation details of hairpin vortices before the onset of transition. The three-dimensional instantaneous pressure field of the hemisphere wake is reconstructed for better understanding the flow mechanism. Experiments are carried out with Reynolds number $Re_{r}=1370$ , based on the hemisphere radius $R$ . Features of periodicity of the near wake are analysed using proper orthogonal decomposition and Fourier transformation. The velocity fluctuation in the wall-normal direction is shown to be crucial to the formation of hairpin vortices in the near wake. By investigating the transport of mass and vorticity, and the correlation between pressure and hairpin vortex strength, the formation mechanism is revealed clearly. Specifically, the main hairpin vortices (MHVs) are formed within the reaction of outer high-speed flow and near-wall flow. The formation of the head portion is followed by the leg portion formation. The shedding of the MHVs is highly correlated with the pressure, as well as the pressure gradient in the wall-normal direction. For the side hairpin vortices (SHVs), the leg portion is formed first, followed by the generation of the head portion thanks to induction of the re-oriented standing vortices. The generation of the SHVs can be regarded as the downstream bridging of the standing vortices, similar to the generation of hairpin vortices due to the connection of streamwise vortices in turbulent boundary layers.

show abstract

supporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Tomographic PIV investigation on near-wake structures of a hemisphere immersed in a laminar boundary layer

Tu,

Wang,

Gao

et al. 2023

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…3(b) is smaller than that in Fig. 3(a), which is obviously caused by the particle phase and is similar to the results behind the hemisphere (Gao et al 2021). Meanwhile, the origin point of streamlines in the recirculation zone moves closer to the cone by approximately 0.2h.…”

Section: Average Velocitysupporting

confidence: 73%

“…2). The liquid-phase flow field was obtained by subtracting the solid-phase flow field from the original flow field (Gao et al 2021). The velocity calculated using this technique did not exceed the maximum relative error of 0.05%.…”

Section: Fig 1 Schematic Diagram Of Experimentalmentioning

confidence: 99%

“…A more intense momentum exchange between large particles and the fluid has a significant effect on the turbulence intensity and Reynolds stress in the near-wall region, while more frequent ejection events occur compared to small particles (Rashidi et al 1990). Moreover, the presence of particles affects the wake structure of the rough element, causing changes in flow characteristics (Gao et al 2021).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Experimental Study of the Particles Influence on the Pyramid Wake within the Turbulent Boundary Layer

2023

JAFM

View full text Add to dashboard Cite

Particle imaging velocimetry (PIV) was used to study the near-field variation of a pyramid rough element in clear water and a liquid-solid boundary layer (thickness: 60 mm). Particles with an average diameter of 355 µm and Stokes number of 4.3 were injected into a 1:1000 mass ratio (solid particles: water) liquid-solid twophase solution. Experiments were conducted to collect instantaneous velocity field information in the streamwise-normal direction and streamwise-spanwise direction at a Reynolds number of 8350. Then, the average velocity field and turbulence intensity of the rough element wake under single-phase and two-phase conditions were compared, and the morphology and periodicity of the shedding structure were analyzed by using proper orthogonal decomposition (POD) combined with the power spectral density function (PSD). Particles were shown to have no significant impact on the recirculation area in the streamwise-spanwise plane but did result in a reduction of the recirculation zone in the streamwise-normal plane and a 0.2h closer location of the streamline's origin to the obstacle. Along with the weakening of the upwash structure, the particle phase diminishes the velocity gradient along the span direction and turbulence intensity. Structural shedding at the top of the pyramid and near the wall occurred simultaneously, and the same shedding period was maintained. Particularly, in the first two POD modes, the energy of the shedding structure near the wall was higher than that at the obstacle tip, with a maximum energy differential of approximately 6%. The Strouhal number of the shedding structure decreased by particles from 0.217 to 0.209. The concentration distribution and degree of dispersion in the particle-laden flow illustrate different results, with lower statistics in the wake flow field.

show abstract

Effects of single circular synthetic jet on turbulent boundary layer

Zhang,

Li,

Ping

et al. 2023

J Hydrodyn

View full text Add to dashboard Cite

The periodic synthetic jet emerging from a circular hole actively controls the turbulent boundary layer (TBL). A time-resolved particle image velocimetry (TR-PIV) system was designed to capture the velocity field database and based on the single-pixel ensemble correlation (SPEC) algorithm, an average drag reduction rate of 6.2% was obtained. The results show that the synthetic jet causes a wide range of low momentum zones and a low-speed streak in the downstream flow field. And the places where the disturbance intensity is strong are often accompanied by a larger velocity deficit. The instantaneous flow fields are visualized with the Finite-Time Lyapunov Exponent (FTLE), and the hairpin vortex packet composed of five hairpin vortices and the generation of new hairpin vortices are observed when there is no control. Under the action of the synthetic jet, the hairpin vortices are continuously generated from the jet hole. The synthetic jet mainly achieves the drag reduction effect mainly by modulating the mean convection term 𝑐 𝐶 and the spatial development term 𝑐 𝐷 . The drag reduction effect appears in the region of 𝑥/𝛿 0 > 0.38, and the maximum drag reduction rate is 12.2% at 𝑥/𝛿 0 = 0.5,, and then gradually decreased. Using proper orthogonal decomposition (POD), it is found that the synthetic jet reduces the energy proportion of the large-scale energetic structures. After the conditional average, the synthetic jet limits the influence range of bursting events at various scales in the near-wall region, and weakens the normal transport of momentum and energy brought about by large-scale ejection events (Q2 events) and the wall friction resistance caused by large-scale sweep events (Q4 events).

show abstract

Experimental investigation on the effect of particles on large scale vortices of an isolated hemispherical roughness element

Cited by 9 publications

References 43 publications

Tomographic PIV investigation on near-wake structures of a hemisphere immersed in a laminar boundary layer

Tomographic PIV investigation on near-wake structures of a hemisphere immersed in a laminar boundary layer

Experimental Study of the Particles Influence on the Pyramid Wake within the Turbulent Boundary Layer

Effects of single circular synthetic jet on turbulent boundary layer

Contact Info

Product

Resources

About