Experimental Studies of Time Mean Flows Around Rectangular Prisms

Mizota, Taketo; Okajima, Atsushi

doi:10.2208/jscej1969.1981.312_39

Cited by 16 publications

(5 citation statements)

References 7 publications

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“…The range of frequencies covered by the power law reduces with increasing downstream distance. The streamwise fluctuations clearly show a strong peak at twice the shedding frequency St s = 0.134, which is consistent with numerous studies (Mizota & Okajima 1981;Norberg 1993;Arslan et al 2012;Portela et al 2017). The 5/3 compensated spectra of the vertical fluctuations shown in figure 7(e) highlight the power law relationship, which lasts for approximately a decade of frequencies.…”

Section: Turbulent Flow Over Cylindersupporting

confidence: 91%

Characterization of energy transfer and triadic interactions of coherent structures in turbulent wakes

Kinjangi,

Foti

2023

J. Fluid Mech.

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Turbulent wakes are often characterized by dominant coherent structures over disparate scales. Dynamics of their behaviour can be attributed to interscale energy dynamics and triadic interactions. We develop a methodology to quantify the dynamics of kinetic energy of specific scales. Coherent motions are characterized by the triple decomposition and used to define mean, coherent and random velocity. Specific scales of coherent structures are identified through dynamic mode decomposition, whereby the total coherent velocity is separated into a set of velocities classified by frequency. The coherent kinetic energy of a specific scale is defined by a frequency triad of scale-specific velocities. Equations for the balance of scale-specific coherent kinetic energy are derived to interpret interscale dynamics. The methodology is demonstrated on three wake flows: (i) ${Re}=175$ flow over a cylinder; (ii) a direct numerical simulation of ${Re}=3900$ flow over a cylinder; and (iii) a large-eddy simulation of a utility-scale wind turbine. The cylinder wake cases show that energy transfer starts with vortex shedding and redistributes energy through resonance of higher harmonics. The scale-specific coherent kinetic energy balance quantifies the distribution of transport and transfer among coherent, mean and random scales. The coherent kinetic energy in the rotor scales and the hub vortex scale in the wind turbine interact to produce new scales. The analysis reveals that vortices at the blade root interact with the hub vortex formed behind the nacelle, which has implications for the proliferation of scales in the downwind near wake.

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Section: Turbulent Flow Over Cylindersupporting

confidence: 91%

Characterization of energy transfer and triadic interactions of coherent structures in turbulent wakes

Kinjangi,

Foti

2023

J. Fluid Mech.

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“…reported in Mizota & Okajima (1981), Sohankar (2006) and Trias et al (2015) for flows at higher Reynolds numbers.…”

Section: Appendix a Further Comparisons With Experiments And Dnsmentioning

confidence: 91%

The turbulence cascade in the near wake of a square prism

2017

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We present a study of the turbulence cascade on the centreline of an inhomogeneous and anisotropic near field turbulent wake generated by a square prism at Re = 3900 using the Kármán-Howarth-Monin-Hill (KHMH) equation. This is the fully generalised scale-by-scale energy balance which, unlike the Kármán-Howarth equation, does not require homogeneity or isotropy assumptions. Our data are obtained from a direct numerical simulation (DNS) and therefore enable us to access all the processes involved in this energy balance. A significant range of length-scales exists where the orientation averaged non-linear interscale transfer rate is approximately constant and negative, indicating a forward turbulence cascade on average. This average cascade consists of coexisting forward and inverse cascade behaviours in different scale space orientations. With increasing distance from the prism but within the near field of the wake, the orientationaveraged non-linear interscale transfer rate tends to be approximately equal to minus the turbulence dissipation rate even though all the inhomogeneity-related energy processes in the scale-by-scale energy balance are significant, if not equally important. We also find well-defined near −5/3 energy spectra in the streamwise direction, in particular at a centreline position where the inverse cascade behaviour occurs for streamwise oriented length-scales.

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“…The vortices could be classi"ed as follows: two-shear-layer related vortices (including the Karman vortex streets and symmetrical vortices), one-shear-layer related vortices, 3-D vortices (including the tip vortex and axial vortex), and others. Bearman & Trueman (1972) and Mizota & Okajima (1981) discussed the drag force related to the formation position of the Karman vortices behind 2-D rectangular cylinders with various side ratios, and they concluded that the close formation of the rectangular rear faces make the drag force large; they also explained the Nakaguchi peak (Nakaguchi et al 1968) of the drag force of a 2-D rectangular cylinder with the speci"c side ratio of 0)64. King (1977) showed the existence of symmetrical vortex shedding behind a circular cylinder at the reciprocal reduced velocity of one-fourth of the Karman vortex resonance reduced velocity, where in-line vibration could be excited.…”

Section: Introductionmentioning

confidence: 99%