Non-modal perturbation growth in a laminar jet: an experimental study

Иванов, О. О.; Ashurov, D. A.; Gareev, L. R.; Vedeneev, Vasily

doi:10.1017/jfm.2023.286

Cited by 5 publications

(5 citation statements)

References 35 publications

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“…PIV measurements in the transverse cut plane of the jet, which are described in Ivanov et al [20] in detail and are not included in this short paper, showed that the evolution of introduced perturbation matches qualitative features of theoretical optimal perturbations quite well. Namely, the following characteristic features of the "lift-up" growth mechanism have been confirmed.…”

Section: Cross Section Visualization and Analysismentioning

confidence: 74%

“…The lengthening of the petals occurs linearly, therefore, the radial velocity perturbation is approximately constant, which is consistent with the theoretical calculations of stationary optimal perturbations of the jet (see fig. 6a at Ivanov et al [20]).…”

Section: Cross Section Visualization and Analysismentioning

confidence: 96%

“…Close-to-linear growth of the axial velocity is in accordance with the development of theoretical optimal perturbations (see fig. 8 at Ivanov et al [20]).…”

Section: Axial Velocity Downstream Evolutionmentioning

confidence: 96%

“…Based on obtained experimental results, we definitely identify the non-modal 'lift-up' growth mechanism of introduced disturbances. The development of perturbations was tracked and compared with the theoretically calculated optimal perturbations [20].…”

Section: Introductionmentioning

confidence: 99%

“…To initiate the non-modal mechanism of perturbations growth, the cross-section distribution of axial velocity perturbation component could qualitatively replicate the same distribution for calculated optimal perturbations (see fig. 7 at Ivanov et al [20]) containing the zones of particles speeding-up and slowing-down so the longitudinal vortex pairs to create. It is also known that stationary perturbations have larger non-modal growth than non-stationary ones [17].…”

Section: Introduction Of Stationary Perturbationsmentioning

confidence: 99%

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Experimental study of perturbation growth in a round laminar jet

Gareev,

Vedeneev,

Ivanov

et al. 2023

Proc Appl Math and Mech

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Jet flows have many applications in various technical processes such as temperature control, mixing, spraying and so forth. Along with wide usage in technology and manufacturing, jet flows are the object of fundamental scientific interest. In particular, a proper understanding of laminar‐turbulent transition in jets is highly important. In this experimental work, we study round laminar submerged jet flow of air and the evolution of controlled perturbations. First, the modal perturbation growth mechanism was under consideration. Thin metal rings were put into the jet at a small distance from the orifice to amplify unstable eigen modes of the jet by oscillating at different frequencies. Experimental and theoretically predicted wavelengths, radial distributions of velocity fluctuations and amplification curves of modal perturbations were compared and a good correspondence was found. Second, the non‐modal perturbation growth mechanism was under consideration. To excite algebraic perturbation growth, we put special wavy structures (deflectors) into the jet, which provide a roller‐like transverse motion in the perturbed jet. The features of the transition to turbulence caused by this non‐modal growth were considered. Based on obtained experimental results, we definitely identify the non‐modal ‘lift‐up’ growth mechanism of introduced disturbances. The development of perturbations qualitatively corresponds to the theoretically calculated optimal perturbations.

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Section: Cross Section Visualization and Analysismentioning

confidence: 74%

Section: Cross Section Visualization and Analysismentioning

confidence: 96%

“…Close-to-linear growth of the axial velocity is in accordance with the development of theoretical optimal perturbations (see fig. 8 at Ivanov et al [20]).…”

Section: Axial Velocity Downstream Evolutionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introduction Of Stationary Perturbationsmentioning

confidence: 99%

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Experimental study of perturbation growth in a round laminar jet

Gareev,

Vedeneev,

Ivanov

et al. 2023

Proc Appl Math and Mech

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On nonmodal stability of elliptic pipe flow

Demyanko,

Klyushnev

2023

Physics of Fluids

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The temporal nonmodal stability of the Poiseuille flow in a pipe of axially uniform elliptic cross section is numerically studied. In particular, it is shown that the maximum amplification of kinetic energy of disturbances depends significantly on the pipe aspect ratio, and this dependence is non-monotonic. It agrees with the corresponding dependence of the energy critical Reynolds number, which is the lower limit of the Reynolds numbers enabling the growth of disturbance kinetic energy. In other words, changing the aspect ratio similarly affects both nonmodal and monotonic stability of the flow. The optimal disturbances displaying the maximum amplification are streamwise counter-rotating vortices. These disturbances are streamwise uniform at sufficiently large Reynolds numbers and may become streamwise harmonic as the Reynolds number decreases. In addition, their symmetry with respect to the cross section axes varies with the aspect ratio. Thus, the obtained results suggest that changing the aspect ratio may be a perspective tool for the passive control of the subcritical laminar-turbulent transition in pipe flows. In other words, this factor is worth considering when designing various devices (e.g., heat exchangers or ventilation systems) containing pipes to enhance their efficiency.

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Optimal disturbances in round submerged jets

Ashurov

2024

Physics of Fluids

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In this paper, optimal growth analysis of spatial disturbances in round submerged jets is performed. Optimal energy growth is studied for various Reynolds numbers Re and frequencies ω. Different velocity profiles proposed by Michalke [“Survey on jet instability theory,” Prog. Aerosp. Sci. 21, 159–199 (1984)] are investigated by varying the shear layer momentum thickness δ, while the jet radius R is considered fixed (as characteristic length). In the case of stationary disturbances, there are no amplified eigenmodes, so eventually the energy of such disturbances decays downstream. Such disturbances are characterized by optimal energy growth as a function of streamwise coordinate z. At certain location downstream zmax this value reaches its maximum Gmax and then decays, although not monotonically, unlike the result of the temporary setting [Jimenez-Gonzalez et al., “Modal and non-modal evolution of perturbations for parallel round jets,” Phys. Fluids 27, 044105 (2015); Jimenez-Gonzalez and Brancher, “Transient energy growth of optimal streaks in parallel round jets,” Phys. Fluids 29, 114101 (2017)]. The well-known scaling Gmax∝Re2 and zmax∝Re is confirmed for stationary disturbances. Conversely, for nonstationary disturbances there is a range of frequencies in which an amplified mode is present. In this case, optimal perturbations far downstream consist only of the amplified mode. The main effect of non-modality here is “the energy pumping” of the amplified mode, so the disturbances are characterized by the “energy ratio” G/Em, i.e., the ratio of the energy of an arbitrary perturbation to the energy of the amplified mode. The influence of the shear layer momentum thickness on optimal disturbances is studied; increasing the shear layer momentum thickness of the base flow “smears” the area occupied by the optimal disturbance, although it does not dramatically affect energy gain values, slightly decreasing maximum energy as shear layer momentum thickness increases. Spatial oscillations in the energy of stationary optimal disturbances in jet flows are discovered. The spectrum structure examination shows that the frequency of these oscillations corresponds to the frequencies of the two least damped discrete eigenmodes.

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Non-modal perturbation growth in a laminar jet: an experimental study

Cited by 5 publications

References 35 publications

Experimental study of perturbation growth in a round laminar jet

Experimental study of perturbation growth in a round laminar jet

On nonmodal stability of elliptic pipe flow

Optimal disturbances in round submerged jets

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