Effects of Crosswind Shear on Trailing Vortex Evolution

Different types of land cover are associated with different surface roughness, which produce variations in the frictional force on the wind. Therefore, mean wind profiles at low levels often differ markedly over short distances where there is a gradient in surface roughness. Horizontal gradients in surface roughness may produce vertical vorticity, circulation, and horizontal divergence. The effect of roughness on vertical wind shear and storm-relative helicity is also qualitatively important and may lead to large gradients in helicity over short distances. Recent studies also suggest an important role of friction in tornadogenesis.
 We show conceptually and theoretically how gradients in surface roughness produce quasi-ambient convergence and vertical vorticity, and gradients in vertical shear and storm-relative helicity. We then present observational data and numerical simulations that demonstrate the effects of surface roughness on the kinematics and shear of boundary-layer flow, for future work examining the importance of these processes for tornadogenesis.

This study numerically investigates the influence of square-wave inlet velocity pulsations on flow structure and heat transfer around a transverse circular cylinder, with particular emphasis on wall condensation behavior. The evolution of wake vortices and the distribution of the convective heat transfer coefficient on the cylinder surface are analyzed under both single-phase and two-phase flow conditions over a range of pulsation frequencies. The results indicate that inlet pulsations significantly modify the wake dynamics, leading to reduced vortex size and enhanced momentum and turbulence dissipation in single-phase flow, which in turn improves convective heat transfer downstream of the separation point. Under two-phase condensation conditions, similar wake modifications are observed, while additional small-scale vortical structures are generated within the condensate film due to interfacial shear, further enhancing local heat transfer. Overall, the findings demonstrate that appropriately tuned inlet pulsations can effectively enhance heat transfer performance for both single-phase and condensing flows around a circular cylinder.

Aircraft wake is a pair of counter-rotating vortices generated behind the aircraft, which can greatly impact the safety of fast takeoff and landing of aircraft and limit the improvement of airport capacity. The current wake parameter retrieval methods cannot locate the wake vortex's position and estimate its strength level in real time. To deal with this issue, a novel algorithm based on YOLOv5s deep learning network is proposed. The new algorithm establishes single vortex locating concept to adapt the wake vortex's evolution at complicate background wind field conditions, and proposes strength-based classification standard which can represent the real-time hazard of wake vortex to shorten the takeoff and landing intervals. Meanwhile, EIOU loss function is introduced to improve the precision of YOLOv5s network. Compared with the state-of-the-art object detection approaches, such as Cascade R-CNN, FCOS, and YOLOv5l, the superiority of new method is demonstrated in terms of accuracy and robustness by using the field detection data from Hong Kong International Airport.

Normal mode solutions are found numerically in a quasi-geostrophic model that includes five or ten vertical levels and either five or nine latitude “levels.” Wind shear and static stability may be adjusted at any of the vertical or latitude levels. Attention is focused on arrangements of static stability and, to a lesser extent, vertical shear that produce large growth rates, while restricting the horizontal gradients of static stability and shear to maintain the validity of the quasi-geostrophic assumption. The association of small static stability and/or large vertical shear in the lower troposphere with large growth rate of short wavelengths found by Staley and Gall is further confirmed. It is also found that rapid amplification of short wavelengths is little diminished even when the small static stability is very localized (in latitude) in the lower troposphere. The perturbations, however, attenuate rapidly away from regions of small static stability. Large static stability above low static s...

A zero inlet swirl turbine rotor (ZISTR) works with axial inlet gas flow directly exhausted from a combustion chamber without any upstream vanes. The suction side trailing edge shock of the ZISTR generates a significant amount of aerodynamic loss. A shock loss reduction method is presented for the ZISTR. The principle of the method is to replace the single shock by double shocks. For minimizing the shock loss, the strength of the double shocks is set to be equal. This is based on a design criterion that multiple shocks should be with equal strength to achieve the minimum shock loss. This design criterion has been widely used for supersonic inlet design, but it is first extended to the transonic turbine design in the present article. A shock model, using aerodynamic relations of oblique shock, is put forward to quantitatively determine the shape of the concave suction-side profile. Numerical simulations indicate that the concave suction-side profile induces a new shock upstream of the suction-side trailing edge shock, and these two shocks are with nearly equal strength in the improved ZISTR. The shock loss of the improved ZISTR is obviously reduced. The concave tip profile would redistribute the blade load on the tip and increase the tip leakage flow loss. Hence, it is suggested that the concave profiles should be designed between 0% and 80% blade span, and the tip profile should keep unchanged. The improved ZISTR with an unchanged tip profile achieves an improvement of turbine efficiency by 0.8% at the design condition.

This paper presents three-dimensional large eddy simulations (LES) and two-dimensional direct numerical simulation (DNS) of wake vortices of an aircraft in a realistic atmospheric boundary layer (ABL). These calculations are performed in order to parametrize an operational model aiming at managing the separations between aircraft at take-off and landing. The computation considered here is taken from twelve selected cases corresponding to trials made at Idaho Falls sponsored by the Federal Aviation Administration (FAA) in 1990. After computing the evolution of a convective atmospheric boundary layer with a non-hydrostatic meteorological model, the evolution of the wake vortices (with their characteristics measured during the experiments) is computed. The threedimensional behavior of the wake vortices as well as the effects of the atmospheric parameters are shown. The results of the simulations are compared to experimental data.

High altitude ER‐2 aircraft observations in both hemispheres of the lower‐stratospheric polar night jet stream reveal generalized scale invariance. The scaling exponent has systematic correlation with wind shear and temperature gradient showing across‐jet persistence, along‐jet anti‐persistence, and an overall average value ≈5/9. The analysis provides a natural connection between generalized scale invariance and traditional large‐scale dynamical meteorology. For one mission in the southern hemisphere composite variograms could be constructed for nitrous oxide and ozone, from which it was deduced that the former is a true passive scalar in the lower stratosphere, while sources and sinks are operative for the latter. Copyright © 2004 Royal Meteorological Society

A model for atmospheric refractive index structure parameter is presented based on low-frequency measurements carried out at a semi-arid region. The model considers wind shear and thermal gradients also as input parameters.

Wake vortex safety analysis and control for unmanned aircraft systems (UAS) operating alongside commercial aircraft in the terminal zones are critical aspects in the integration of UAS into the National Airspace System (NAS), particularly in terminal airspace. We address an approach that integrates reduced-order models of wake generation, evolution, interaction and its control incorporating both theoretical and high-fidelity predictions. Our previous study [1] estimated UAS responses in terms of the roll control ratios (RCR) developed by the follower aircraft depending on their position and orientation relative to the wake shed by the leader aircraft, as well as the duration of the wake-UAS interaction. The current paper complements and expands the previous study to describe a predictive, robust feedback-loop flight control model that is applicable to various classes of UAVs in unsteady flight-path scenarios including control of wake response. The control design presented in this paper extends previous research results by first demonstrating asymptotic (zero steady-state error) altitude regulation control in the presence of unmodeled vertical wind gust disturbances. To address the practical considerations involved in small UAV applications with limited computational resources, the proposed control method is designed with a computationally simplistic structure, without the requirement of complex calculations or function approximators in the control loop. Proof of the theoretical result is summarized, and detailed numerical simulation results are provided, which demonstrate the capability of the proposed nonlinear control method to asymptotically reject wind gust disturbances and parameter variations in the state space model. Simulation comparisons with a standard linear control method are provided for completeness.

A novel workflow based on physics-informed machine learning to determine the permeability profile of fractured coal seams using downhole geophysical logs

Sediment-laden surface vortices in pump sump represent a three-phase flow, comprising gas, liquid, and solid phases, surpassing the complexity of clear water vortices, which has also more serious effect on the hydraulic machinery. In this paper, focusing on sediment-laden free surface vortices, a model experiment was employed to investigate their motion characteristics. The spatiotemporal evolution of sediment-laden vortices has been captured through three-dimensional velocity testing, revealing particle aggregation and dispersion patterns within vortex cores at various stages. Radial velocity within the vortex core accelerates the inward movement of particles, while axial velocity enhances their vertical transport. The scale of sandy vortices is larger than that of clear water vortices, approximately 1.2 times the size, and the rotational velocity within the vortex core is lower for sandy vortices, with maximum rotational velocities of 1.04 and 0.5 m/s, respectively. The maximum suction speed of the vortex is 6.1 times that of the initial stage, and the sediment-carrying capacity is 21 times greater. Finally, the mechanism and characteristics of vortex transporting sand and air are discussed, along with the detrimental effects of various sediment-carrying vortices on the sediment erosion of hydraulic machinery. The research findings of this paper have significant theoretical and engineering values.

In order to study the wake vortices generated by landing aircrafts, we conducted an experiment on the airfield of Tolmachevo Airport in 2018, which involved the Stream Line lidar, AMK-03 sonic anemometer and MTP-5 temperature profiler. The experiment determined the limits of applicability of the radial velocity method used to obtain estimates of the parameters of wake vortices from lidar measurements, depending on the type of aircraft and the intensity of wind turbulence. An analysis of the experimental results made it possible to identify a number of features of the spatial dynamics and evolution of aircraft wake vortices during different states of the surface layer of the atmosphere. In particular, it was found that in the case of low average lateral wind speed and moderate wind turbulence, the lifetime of the vortex formed behind the landing aircraft MD-11F can reach almost 4 minutes.

In order to study the wake vortices of landing aircraft, we carried out an experiment on the airfield of Tolmachevo Airport in 2018 using Stream Line lidar, an AMK-03 sonic anemometer, and an MTP-5 temperature profiler. The limits of applicability of the method of radial velocity in estimation of wake vortex parameters from lidar measurements were determined for different aircraft types and wind turbulence strength. The analysis of the experimental results makes it possible to identify features of the spatial dynamics and evolution of aircraft wake vortices under different states of the surface air layer. In particular, we found that the lifetime of a vortex generated behind a large MD-11F aircraft on landing can reach 4 min in the case of low average crosswind speed and moderate wind turbulence.

Wingtip vortices are an important phenomenon in fluid dynamics due to their complex and negative impacts. Despite numerous studies, the current understanding of the inner vortex is very limited; thus, a basis for the design of effective wingtip geometry and vortex manipulation is narrow. This work examines the structure of the trailing vortex shed from a swept-tapered wing, analogous to a commercial aircraft topology. Stereoscopic particle imaging velocimetry has been utilized to compare the vortex structure and development through several angles of attack at various downstream stations for a fixed Reynolds number (Re = 1.5 × 106). After correcting for vortex meander through helicity-based spatial localization of the vortex core, relationships between the vortex core velocity/vorticity fields, core shape, and turbulent properties have been examined. Subsequently, the vortex is found to exhibit a layered structure with slow linear rates of dissipation indicative of laminar diffusion mechanisms, despite being a turbulent vortex. The turbulent kinetic energy distribution in the vortex signals that relaminarization of the inner core occurs. Consideration of the streamline curvature around the core, via examination of the local Richardson number, indicated that a laminar core structure had formed within which large-scale turbulent eddies could not contribute to the turbulent diffusion of vorticity away from the core. The normalized circulation within the vortex core has been shown to exhibit self-similar behavior typical of the fully developed axisymmetric vortices.

The energy and momentum balance of an abyssal overflow across a major sill in the Samoan Passage is estimated from two highly resolved towed sections, set 16 months apart, and results from a two-dimensional numerical simulation. Driven by the density anomaly across the sill, the flow is relatively steady. The system gains energy from divergence of horizontal pressure work and flux of available potential energy . Approximately half of these gains are transferred into kinetic energy while the other half is lost to turbulent dissipation, bottom drag, and divergence in vertical pressure work. Small-scale internal waves emanating downstream of the sill within the overflow layer radiate upward but dissipate most of their energy within the dense overflow layer and at its upper interface. The strongly sheared and highly stratified upper interface acts as a critical layer inhibiting any appreciable upward radiation of energy via topographically generated lee waves. Form drag of , estimated from the pressure drop across the sill, is consistent with energy lost to dissipation and internal wave fluxes. The topographic drag removes momentum from the mean flow, slowing it down and feeding a countercurrent aloft. The processes discussed in this study combine to convert about one-third of the energy released from the cross-sill density difference into turbulent mixing within the overflow and at its upper interface. The observed and modeled vertical momentum flux divergence sustains gradients in shear and stratification, thereby maintaining an efficient route for abyssal water mass transformation downstream of this Samoan Passage sill.