Controlled Synthetic Freestream Turbulence Intensity Introduced by a Local Volume Force

Tangermann, Eike; Klein, Markus

doi:10.3390/fluids5030130

Cited by 6 publications

(4 citation statements)

References 26 publications

(30 reference statements)

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“…In the Appendix A, we compare the temporal evolution of turbulence metrics of our forcing approach with that by Carroll and Blanquart. [ 37 ] The enhancement of volume forcing by using controllers is also reported in the recent literature [ 41,52 ] for different applications.…”

Section: Methodsmentioning

confidence: 97%

Effect of turbulence intensity and surface tension on the emulsification process and its stationary state—A numerical study

et al. 2022

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We study turbulent emulsions and the emulsification process in homogeneous isotropic turbulence (HIT) using direct numerical simulations (DNS) in combination with the volume of fluid method (VOF). For generating a turbulent flow field, we employ a linear forcing approach augmented by a proportional‐integral‐derivative (PID) controller, which ensures a constant turbulent kinetic energy for two phase flow scenarios and accelerates the emulsification process. For the simulations, the density ratio of dispersed and carrier phases is chosen to be similar to that of oil and water (0.9), representing a typical application. We vary the turbulence intensity and the surface tension coefficient. Thus, we modulate those parameters that directly affect the Hinze scale, which is expected to be the most stable maximum droplet diameter in emulsions in HIT. The considered configurations can be characterized with Taylor Reynolds numbers in the range of 100–140 and Weber numbers, evaluated with the velocity fluctuations and the integral length scale, of 4–70. Using the 3‐D simulation results, we study the emulsification process as well as the emulsions at a statistically stationary state. For the latter, droplet size distributions are evaluated and compared. We observe a Hinze scale similarity of the size distributions considering a fixed integral length scale, that is, similar Hinze scales obtained at different turbulence intensities or for different fluid properties result in similar distributions.

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Section: Methodsmentioning

confidence: 97%

Effect of turbulence intensity and surface tension on the emulsification process and its stationary state—A numerical study

et al. 2022

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“…With this definition, the volume force distribution is assumed to be constant in the streamwise direction x 1 within a given generation volume V g and zero outside. The effect of the streamwise extension of this region on the perturbation generated by the volume forces has been discussed in [32].…”

Section: Turbulence Production and Control Methodologymentioning

confidence: 99%

Turbulent Eddy Generation for the CFD Analysis of Hydrokinetic Turbines

Gregori¹,

Salvatore²,

Camussi³

2022

Preprint

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This paper presents a novel theoretical and computational methodology for the generation of an onset turbulent field with prescribed properties in the numerical simulation of an arbitrary viscous flow. The methodology is based on the definition of a suitable distribution of volume force terms in the right–hand side of the Navier–Stokes equations. The distribution is represented by harmonic functions that are randomly variable in time and space. The intensity of the distribution is controlled by a simple PID strategy in order to obtain that the generated turbulent flow matches a prescribed turbulence intensity. A further condition is that a homogeneous isotropic flow is es- tablished downstream of the region where volume force terms are imposed. Although it is general, the proposed methodology is primarily intended for the computational modelling of hydrokinetic turbines in turbulent flows representative of tidal or riverine installations. A first numerical applica- tion is presented by considering the injection of homogeneous and isotropic turbulence with 16% intensity into a uniform unbounded flow. The analysis of statistical properties as auto-correlation, power spectral density, probability density functions, demonstrates that the generated flow tends to achieve satisfactory levels of stationarity and isotropy, whereas the simple control strategy used determines overestimated turbulent intensity levels.

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“…The method has been described in detail in Reference. 7 A force term F syn is added to the momentum equation.…”

Section: Synthetic Turbulencementioning

confidence: 99%

“…Their calibration has been described in Reference. 7 The overall setup is shown in Figure 2 with the forcing zone marked red located approximately 0.75c upstream of the leading edge followed immediately by the measurement zone marked yellow. It also can be seen how the mesh is refined within the turbulent region.…”

Section: Synthetic Turbulencementioning

confidence: 99%

Numerical Simulation of a Separating Laminar Boundary Layer Exposed to Ambient Turbulence

Tangermann¹,

Klein²

2021

14th WCCM-ECCOMAS Congress

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Laminar separation on wings exposed to flow of a low Reynolds number is a very common phenomenon already at low angles of attack. It is extremely sensitive to turbulence in the freestream as is can affect the boundary layer upstream of the separation, the transition into turbulence and at very large length scales also locally change the angle of attack. Hybrid RANS/LES simulations of laminar separation haven been performed with parametric variations of both intensity and length scale of the ambient turbulence. The boundary layer has then been analyzed in order to demonstrate the effect of eddies impinging the laminar boundary layer upstream of the separation leading to stabilizing and destabilizing effects, which both have been identified and visualized.

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Controlled Synthetic Freestream Turbulence Intensity Introduced by a Local Volume Force

Cited by 6 publications

References 26 publications

Effect of turbulence intensity and surface tension on the emulsification process and its stationary state—A numerical study

Effect of turbulence intensity and surface tension on the emulsification process and its stationary state—A numerical study

Turbulent Eddy Generation for the CFD Analysis of Hydrokinetic Turbines

Numerical Simulation of a Separating Laminar Boundary Layer Exposed to Ambient Turbulence

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