Fluid Dynamics Research

Poole, Ryan; Turner, M R

2024 Fluid Dynamics Research

doi: 10.1088/1873-7005/ad7aa0

Jets and wakes are fundamental fluid flows that arise in a wide range of environmental and aerospace applications. They are typically studied as open systems. Here we are interested in the implications of placing the jet or wake inside of another system, as well as the implications of compliant walls. In particular, the effect of asymmetry is considered on the absolute instability properties for this internal flow, when it is transversely confined by compliant walls. Two distinct cases are considered, namely the case of two compliant walls with non-identical wall parameters and the case of identical compliant walls asymmetrically located about the fluid center line. The absolute instability characteristics are identified by following special saddle points (pinch points) of the dispersion relation in the complex wavenumber plane, and the flow’s stability properties are mapped out using parameter continuation techniques. The compliant walls introduce new modes which typically dominate the stability properties of the flow, in comparison to the case of pure shear layers. In the case of symmetrically located walls with non-identical wall parameters, it was found that the absolute stability properties are dominated by the modes linked to the more flexible of the two walls. In the case of identical walls asymmetrically confining the flow, it was found that these flows exhibit smaller regions of absolute instability in parameter space, when compared to the symmetric flow configuration.

Khairi, Muthana Mraweh; Razavi, Seyed Esmail; Talati, Faramarz; Ehghaghi Bonab, Mir Biuok

2024 Fluid Dynamics Research

doi: 10.1088/1873-7005/ad7400

In this research, a three-dimensional turbulent wall jet was modeled using an Improved Delayed Detached Eddy Simulation to examine its flow and thermal properties. The accuracy of the simulation was confirmed by comparing key flow characteristics with experimental data. The study involved introducing an oscillating wall and a hot wall within the computational domain to observe their effects on thermal behavior and turbulence structure. OpenFOAM v2012 was utilized for the simulations based on a 3D channel design. The turbulent structure exhibited distinct separated, small-scale, and large-scale turbulence within the domain. The findings indicated that reducing the computational domain height increased the Nusselt number, and positioning the hot wall near the core of the jet also increased the Nusselt number. Additionally, increasing the frequency and amplitude of the oscillating wall resulted in a higher Nusselt number. These results contribute to a deeper understanding of the fluid physics in this specific scenario and can enhance knowledge in the fields of solid and turbulence fluid structure interaction. The analysis of the turbulence structure revealed that a lower domain height created elongated turbulence structures, and placing the hot wall at the end of the computational domain had less impact on smoothing the turbulence structures due to the presence of very strong, large turbulence structures.

Kumar, Rakesh; Sharma, Tanya

2024 Fluid Dynamics Research

doi: 10.1088/1873-7005/ad73ff

The present work examines the linear stability of non-linear convected flow inside a Riga plate channel. The channel is filled with hybrid nanoliquid and is under the novel influence of the partial slip phenomenon in the present scenario. The left domain of the channel is supported by the Riga sheet whereas the right part is bounded by a sheet of slippery nature. The stability model for this partial slip mechanism is developed in the form of an eigenvalue problem which is explored via the Chebyshev pseudospectral method in combination with the QZ-algorithm. It is reported that the convection forces in hybrid nanofluid are amplified with Riga magnetic number (Hr) under slip/no-slip assumptions. It is interestingly noted that the flow is destabilized by 11.47% with non-linear convection (Nc) when considering no-slip at the right-hand sheet. However, the stability region is enlarged with Nc by 9.53% in the presence of slip at the right-hand sheet. The partial-slip (γ) assumption in the channel decelerates the growth rate of disturbances. The increment in Fe3O4-nanoparticles over the fixed volume of CoFe2O4-nanoparticles hampers the instability of the hybrid nanofluid mixture.

Kawaguchi, Mikimasa; Iwasaki, Masato; Nakayama, Ryoutaro; Yamamoto, Ryo; Nakashima, Akira; Ogata, Yoichi

2024 Fluid Dynamics Research

doi: 10.1088/1873-7005/ad716a

Analysis methods based on mode decomposition have been proposed to describe the characteristics of flow phenomena. Among them, proper orthogonal decomposition (POD), which decomposes modes into eigenvalues and basis vectors, has long been used. Many studies have shown that POD is a useful method for capturing the characteristics of unsteady flow. In particular, Snapshot POD has attracted much recent attention and has been used to solve unsteady flow problems. However, the basis vectors of the mode obtained by conventional POD is different for each condition. Therefore, whether the basis vectors of each mode are switching in the direction of parameters (e.g. different shapes or different Reynolds numbers) or whether they develop or decay is difficult to discuss. As a result, discussions on conventional POD tend to be qualitative. To address this issue, the present study uses Parametric Global POD, a method that perfectly matches basis vectors in results with different parameters (in this study, different Reynolds numbers). Parametric Global POD method was applied to the analysis of the flow field in a curved pipe and found to capture the development or decay of modes with major basis vectors in the direction of parameters, which is difficult to achieve with conventional POD methods.