Investigation of wakes generated by fractal plates in the compressible flow regime using large-eddy simulations

Es-Sahli, Omar; Sescu, Adrian; Afsar, Mohammed; Buxton, O. R. H.

doi:10.1063/5.0018712

Cited by 10 publications

(6 citation statements)

References 63 publications

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“…Yet, in the last years, evidence has been found that some axisymmetric turbulent wakes do not follow the standard scalings of U and δ. Different experimental studies and direct numerical simulations of bluff plates with both regular and irregular peripheries found that C ε is not constant, but instead it goes as C ε ∼ Re m G /Re n L (e.g., Vassilicos, 2015;Dairay et al, 2015;Obligado et al, 2016;Nedic et al, 2013;Es-Sahli et al, 2020). Re G is a Reynolds number that depends on the inlet conditions, and Re L is a local, streamwise, position-dependent one (Vassilicos, 2015).…”

Section: Introductionmentioning

confidence: 99%

Application of the Townsend–George theory for free shear flows to single and double wind turbine wakes – a wind tunnel study

2022

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Abstract. The evolution of the mean velocity and the turbulence downstream of wind turbine wakes within the atmospheric boundary layer has been studied over the past decades, but an analytical description is still missing. One possibility to improve the comprehension of this is to look into the modeling of turbulent bluff body wakes. There, by means of the streamwise scaling of the centerline mean velocity deficit, the nature of the turbulence inside a wake can be classified. In this paper, we introduce the analytical model of classical wake theory as introduced by Albert Alan Townsend and William Kenneth George. To test the theories, data were obtained from wind tunnel experiments using hot-wire anemometry in the wakes of a single model wind turbine and a model wind turbine operating in the wake of an upstream model wind turbine. First, we test whether the requirements under which the Townsend–George theory is valid are fulfilled in the wake of a wind turbine. Based on this verification we apply the Townsend–George theory. Further, this framework allows for distinguishing between two types of turbulence, namely equilibrium and non-equilibrium turbulence. We find that the turbulence at the centerline is equilibrium turbulence and that non-equilibrium turbulence may be present at outer parts of the wake. Finally, we apply the Townsend–George theory to characterize the wind turbine wake, and we compare the results to the Jensen and the Bastankhah–Porté-Agel models. We find that the recent developments from the classical bluff body wake formalism can be used to further improve the wind turbine wake models. Particularly, the classical bluff body wake models perform better than the wind turbine wake models due to the presence of a virtual origin in the scalings, and we demonstrate the possibility of improving the wind turbine wake models by implementing this parameter. We also see how the dissipation changes across the wake, which is important to model wakes within wind farms correctly.

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Section: Introductionmentioning

confidence: 99%

Application of the Townsend–George theory for free shear flows to single and double wind turbine wakes – a wind tunnel study

2022

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“…The LES model simulates the transient flow field [16][17][18][19]. In the LES, based on the eddy scale, the vortex is divided into two parts, namely large and small eddies.…”

Section: Numerical Models and Methodsmentioning

confidence: 99%

Numerical Simulation of 3D Flow Field and Flow-Induced Noise Characteristics in a T-Shaped Reducing Tee Junction

Lv¹,

Wang²,

Guo³

et al. 2023

Fluid Dynamics &Amp; Materials Processing

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The so-called T-shaped reducing tees are typically used to divide, change and control (to a certain extent) the flow direction in pipe networks. In this study, the Ffowcs Williams-Hawkings (FW-H) equation and the Large Eddy Simulation (LES) methods are used to simulate the flow-induced noise related to T-shaped reducing tees under different inlet flow velocities and for different pipe diameter ratios. The results show that the maximum flow velocity, average flow velocity, and vorticity in the branch pipe increase gradually as the related diameter decreases. Strong vorticity and secondary flows are also observed in the branch pipe, and the associated violent pressure fluctuations are found to be the main sources of flow-induced noise. In particular, as the pipe diameter ratio decreases from 1 to 0.45, the Total Sound Pressure Level (TSPL) increases by 6.8, 6.26, and 7.43 dB for values of the inlet flow velocity of 1, 2, and 3 m/s, respectively. The distribution characteristics of the flow-induced noise in the frequency domain follow similar trends for different pipe diameter ratios.

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“…The hybrid CFD/CAA method was used to study flow and sound field of the baseline and the WIW-treated nozzles. The LES method, which has been proved to be a robust tool for the prediction of the jet noise [16][17][18][19], is applied in the near field. And the Ffowcs Williams and Hawkings [20] (FW-H) integration is used for far field prediction.…”

Section: Governing Equationsmentioning

confidence: 99%

Noise control for high subsonic jet by inner wall treatment

Mao

Tang

Yang

et al. 2023

Preprint

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Subsonic jet nozzles, commonly used in passenger aircrafts, generate significant noise that travels both downstream and upstream due to large-scale or fine-scale turbulences in the jet plume. To reduce jet noise, a novel wall treatment method, termed the wavy inner wall (WIW), is proposed. With this method, the smooth inner wall near the exit of the nozzle is replaced by treated walls that carry small wavy patterns. Numerical simulations are conducted to investigate the effects of the WIW treatment. Large eddy simulations (LES) were used to predict the unsteady flow field and the far-field noise, followed by the analogy method proposed by Ffowcs Williams and Hawkings. To better understand the mechanism behind the noise reduction achieved by the WIW treatment, the shear-layer instability, radial and azimuthal auto-correlation functions, turbulent kinetic energy, and acoustic source term from the Tam-Auriault (TA) jet-noise model were analyzed. Results indicated that the WIW treatment advances the onset of jet flow instability in the shear-layer, leading to the early breakdown of jet shear-layer and production of different scales of downstream turbulent structures. As a result, the distribution and production of turbulent kinetic energy are affected, and the generation and emission of jet noise are controlled. The WIW treatment enables the control of fine scale turbulence, resulting in the reduction of mid- to high-frequency noise in the far field, while ensuring a low thrust loss. This feature makes the WIW method a promising approach for jet noise control.

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Investigation of wakes generated by fractal plates in the compressible flow regime using large-eddy simulations

Cited by 10 publications

References 63 publications

Application of the Townsend–George theory for free shear flows to single and double wind turbine wakes – a wind tunnel study

Application of the Townsend–George theory for free shear flows to single and double wind turbine wakes – a wind tunnel study

Numerical Simulation of 3D Flow Field and Flow-Induced Noise Characteristics in a T-Shaped Reducing Tee Junction

Noise control for high subsonic jet by inner wall treatment

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