The Search for Atmospheric Laminar Channels: Experimental Results and Method Dissemination

In this paper, a practical application of theoretical developments found in our previous works is explored in relation to atmospheric lidar data. Multifractal structures, previously named “laminar channels”, have been identified in atmospheric profiles—these exhibit cellular and self-structuring properties, and are spatially ordered across the atmospheric profile. Furthermore, these structures have been connected to the spontaneous emergence of turbulent behavior in the calm atmospheric flow. Calculating the location and occurrence of these channels can help identify features of atmospheric evolution, such as the development of the planetary boundary layer (PBL). Employing this theoretical background to atmospheric lidar data, attempts are made to confirm this suggestion and extract information about atmospheric structure and evolution by analyzing turbulent vortex scale dynamics and scale-corresponding Lyapunov exponents that form the basis of identifying the laminar channels in atmospheric lidar profiles. A parameter named “scale laminarity index” is then introduced, which quantifies the relation between vortex scale and chaoticity throughout the profile. Finally, the algorithmic methods employed in this study are described and distributed for future use.

Control of Sunroof Buffeting Noise by Optimizing the Flow Field Characteristics of a Commercial Vehicle

When a commercial vehicle is driving with the sunroof open, it is easy for the problem of sunroof buffeting noise to occur. This paper establishes the basis for the design of a commercial vehicle model that solves the problem of sunroof buffeting noise, which is based on computational fluid dynamics (CFD) numerical simulation technology. The large eddy simulation (LES) method was used to analyze the characteristics of the buffeting noise with different speed conditions while the sunroof was open. The simulation results showed that the small vortex generated in the cab forehead merges into a large vortex during the backward movement, and the turbulent vortex causes a resonance response in the cab cavity as the turbulent vortex moves above the sunroof and falls into the cab. Improving the flow field characteristics above the cab can reduce the sunroof buffeting noise. Focusing on the buffeting noise of commercial vehicles, it is proposed that the existing accessories, including sun visors and roof domes, are optimized to deal with the problem of sunroof buffeting noise. The sound pressure level of the sunroof buffeting noise was reduced by 6.7 dB after optimization. At the same time, the local pressure drag of the commercial vehicle was reduced, and the wind resistance coefficient was reduced by 1.55% compared to the original commercial vehicle. These results can be considered as relevant, with high potential applicability, within this field of research.

Diagnosis of Pre-Depression Large-Scale Vortex Instability in the Tropical Atmosphere

<p>An approach is proposed [1] for determining the precise time of the start of tropical cyclogenesis, which includes a combined analysis of data from cloud-resolving numerical modeling and GOES Imagery. The approach is based on the similarity of patterns in the fields of vertical helicity (numerical simulation) and temperature (satellite data), allowing for the localization of intense rotating convective clouds known as the Vortical Hot Towers. As a theoretical ground, we applied a hypothesized (to date) interpretation of tropical cyclogenesis as a large-scale instability caused by the mechanism of the turbulent vortex dynamo in the atmosphere [1,2], and with bearing in mind the crucial role of Vortical Hot Towers in providing the dynamo-effect [2]. In this context, birth of a hurricane is considered as an extreme threshold event in the helical atmospheric turbulence of a vorticity-rich environment of a pre-depression cyclonic recirculation zone. Helical turbulence is characterized by the broken mirror symmetry and permits an existence of inverse energy cascade in three-dimensional cases. In order to trace and analyze processes of self-organization in the tropical atmosphere, that span scales from convective clouds with horizontal dimensions of 1-5 km to mesoscale vortices of hundreds of kilometers, we used the post-processing [1-3] of data from cloud-resolving numerical simulations [4].  Implementation of the proposed approach revealed that large-scale vortex instability can begin a few hours, or even dozens of hours, before the formation of the Tropical Depression. This work was supported by the research project “Monitoring” No. 01200200164.</p><p>References</p><p>[1] Levina, G. V., 2020. Birth of a hurricane: early detection of large-scale vortex instability. J. Phys.: Conf. Ser., <strong>1640  </strong>012023,  doi:10.1088/1742-6596/1640/1/012023</p><p>[2] Levina, G. V., 2018. On the path from the turbulent vortex dynamo theory to diagnosis of tropical cyclogenesis. Open J. Fluid Dyn., <strong>8,</strong> 86–114,  https:<strong>//</strong>doi.org/10.4236/ojfd.2018.81008</p><p>[3] Levina, G. V. and M. T. Montgomery, 2015. When will Cyclogenesis Commence Given a Favorable Tropical Environment?  Procedia IUTAM, <strong>17</strong><strong>,</strong> 59–68, https://doi.org/10.1016/j.piutam.2015.06.010</p><p>[4] Montgomery, M. T., M. E.  Nicholls, T. A. Cram, and A. B. Saunders, 2006: A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci., 63, 355–386,  https://doi.org/10.1175/JAS3604.1</p>

ON ONE APPROACH TO DETERMINING THE VORTEX SOUND SOURCE

The work consists of five sections and a bibliographic list. The first section provides answers to questions about the relevance, the applied value of the study, as well as the need to develop new approaches that allow modeling vortex structures in engineering practice. In the second section, some mathematical models and approaches used to solve problems of vortex dynamics are considered. The third section is devoted to solving the problem of determining the main parameters of the flow in the core of a vortex ring for given geometric dimensions. It is shown that a turbulent vortex ring is obtained as a result of the interaction of two vortex columns. The fourth section is devoted to methods for characterizing a concentrated vortex as a source of acoustic vibrations. As an object of research, the flow in the core of a turbulent vortex ring is considered. It is assumed that the core of the vortex ring has the shape of a torus. An approach is proposed that makes it possible to establish a strict link between the main flow parameters and the shape of the vortex ring. The aim of this work is to obtain the flow parameters in the core of a vortex ring with their subsequent substitution into the acoustic-vortex equation to analyze the source of acoustic oscillations. It is also necessary to show the presence of a structure in the vortex ring corresponding to some point symmetry and, thus, to abandon the concept of the circular symmetry of the core of the vortex ring. The proposed approach is based on the assertion that a vortex ring can be represented as a set formed according to a “rule” that determines a spatial geometric shape. As a result, an approach was proposed for analyzing the vortex ring as a source of acoustic oscillations, and it was also formulated and theoretically substantiated that the core of a turbulent vortex ring having the shape of a torus can be considered as a result of the interaction of two vortex columns.

Investigation on the Fluctuations of the Spray Angle Generated From Pressure-Swirl Atomizers

The unsteady characteristic of the pressure-swirl atomization system was studied experimentally in this paper. It was found that the fluctuations of the spray can be divided into two modes: high and low frequency mode, among which the frequency of the high mode is within the range of 500–1100Hz, and the low mode is 100–400Hz. The low mode depends on the turbulent exchange of momentum between the liquid and the surrounding stagnant gas. While the high mode depends on the comprehensive effect of the turbulent vortex generated by the liquid flowing through the atomizer and the natural frequency of the atomizer. Experiments show that the peak frequency of the low mode increases but the peak frequency of the high mode decreases when the pressure drop of the atomizer increases. When the atomizer outlet area size increases, both the peak frequency of the low mode and the high mode decrease. When the deflection angle of the swirl chamber increases, the peak frequency of the low mode increases, while the peak frequency of the high mode decreases first and then increases, reaching the minimum at 60°, and the value at 45° is basically the same as at 80°.