Topic
Vortex sheet
About: Vortex sheet is a research topic. Over the lifetime, 1601 publications have been published within this topic receiving 35497 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this paper, a conceptual model based on an analytical theory of von Karman vortex streets affected by stratification and differential rotation was developed for periodic coherent vortex structures arising in geophysical turbulent flows at low Rossby number.
Abstract: In this study self-organized periodic coherent vortex structures arising in geophysical turbulent flows at low Rossby number are investigated by developing a conceptual model based on an analytical theory of von Karman vortex streets affected by stratification and differential rotation. In the framework of a quasi-geostrophic (QG) two-layer beta-plane model vortex streets with three different types of vertical structures (barotropic, upper layer and hetonic) are analysed using the point vortex approximation. The streets are found to be exact solutions of the potential vorticity equation and to be characterized by four non-dimensional parameters. Von Karman streets are semi-localized solutions which form a bridge between vortex pairs (limit of symmetric dilute streets) and two parallel vortex sheets (limit of dense streets). On the beta-plane QG von Karman streets can only move to the east, i.e. with a speed outside the range of speeds of Rossby waves, so that a dynamical asymmetry in the zonal direction is introduced. A complete classification on a diagram of states shows that critical bounds exist in the parameter space, prescribing for example a maximum distance between vortex rows beyond which no QG vortex streets can be found. Typically a fast and a slow vortex street with different flow structures are found in the region of existence. As a function of distance between vortex rows baroclinic QG vortex streets show a characteristic non-monotonic speed behaviour at scales of the order of the baroclinic Rossby radius. A wide region of possible existence of QG von Karman streets is found in atmospheric, oceanic and planetary conditions as well as in rotating tank experiments. The theory can be applied to describe the coherent part of turbulent baroclinic intermittent zonal jet-like and frontal flows and provides a scaling for such flows.
25 citations
TL;DR: In this paper, it is shown that the baroclinic vorticity generated at the leading edge of the cold pool is transported rearward in the vortex sheet along the interface between cold and warm air, and the barotropic vortivity associated with environmental shear is conserved along streamlines.
Abstract: Two aspects of vorticity associated with cold pools are addressed. First, tilting of horizontal vortex tubes by the updraft at a gust front has been proposed as a means of getting near-ground rotation and hence a tornado. Theory and a numerical simulation are used to show that this mechanism will not work because warm air parcels approaching the gust front decelerate in strong adverse pressure gradient. The near-surface horizontal vorticity available for upward tilting is greatly reduced by horizontal compression before it is tilted. Consequently, uplifting of vortex tubes produces little vertical vorticity near the ground.Second, it is shown that the baroclinic vorticity generated at the leading edge of the cold pool is transported rearward in the vortex sheet along the interface between cold and warm air, and the barotropic vorticity associated with environmental shear is conserved along streamlines. Warm parcels away from the interface do not acquire baroclinic vorticity to offset their barotro...
25 citations
TL;DR: A method for imaging a moving fluid by appropriately combining travel times, projections of both the sound speed and the velocity are isolated and the component of fluid vorticity transverse to the plane of insonification is recovered.
Abstract: A new method for imaging a moving fluid using acoustic tomography is evaluated by numerical simulation. A cross section of the medium is probed by high‐frequency acoustic waves from several different directions. It can be shown that the resulting measured travel time data contain sufficient information to reconstruct both the spatially varying sound speed and the transverse component of the fluid vorticity [K. B. Winters and D. Rouseff, Inverse Problems 6, L33 (1990)]. The results are exact to within the validity of the straight‐ray geometric acoustics approximation. To evaluate a discrete version of the reconstruction algorithm, a three‐dimensional stably stratified mixing layer is simulated. The flow exhibits characteristic features in both density (sound speed) and vorticity. The dynamics of the fluid flow can be described as the instability of a vortex sheet. The acoustic travel time is calculated by integrating through the simulated flow fields. The synthetic data are then inverted to yield reconstru...
25 citations
TL;DR: Theoretical and experimental results show that the expansion end correction is significantly affected by the flow and hydrodynamic waves excited at the edge of the expansion, and the effects are different in three regions where the Strouhal number is small, of order 1, and large.
Abstract: For scattering of plane waves at a sudden area expansion in a duct, the presence of flow may significantly alter the reactive properties. This paper studies the influence of a mean flow field and unstable separated flow on the reactive properties of the expansion, formulated as an end correction. Theoretical and experimental results show that the expansion end correction is significantly affected by the flow and hydrodynamic waves excited at the edge of the expansion. The effects are different in three regions where the Strouhal number is small, of order 1, and large. The influence is most significant at Strouhal numbers of the order 1, with specific limiting values for large and small Strouhal numbers, respectively. In the analytic model, an important feature is the shear layer at the edge modeled as a vortex sheet with the unsteady Kutta condition applied at the edge. The influence of Mach number, Helmholtz number, and area expansion ratio is studied, and a quasistationary, small Strouhal number, approximation yields an expression for the end correction. Further, the influence of edge condition is explored, emphasizing the importance of interaction between sound and unsteady vorticity shedding at the edge of the area expansion.
25 citations
TL;DR: The applicability of the vortex method to cascades of oscillating airfoils is assessed by computing the unsteady incompressible lift, drag, and moment for small incidence, thickness, and vibratory displacement as discussed by the authors.
Abstract: The applicability of the vortex method to cascades of oscillating airfoils is assessed by computing the unsteady incompressible lift, drag, and moment for small incidence, thickness, and vibratory displacement—the so-called "classical" case. The results for a limited sampling of cascade geometries, reduced frequencies, vibration amplitudes, and interblade phase angles are in excellent agreement with available analytical results. Instantaneous streamline patterns and discretized vorticity distributions are presented as an aid in physical understanding. The importance of the interblade phase angle as a governing parameter is confirmed. Then the effects of mean incidence, vibration amplitude, and stagger angle are studied. Important new results are presented showing the evolution of the classical reactions into the stalled-flow reactions with incidence, frequency, and amplitude as parameters. In particular, the complicated interaction is demonstrated between the structural frequency of the blades (considered as one of the "inputs" to a nonlinear aeroelastic system) and the output frequency spectrum of the aerodynamic reactions. The implications for future direction of research and design code implementation are discussed.
24 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 3 |
| 2024 | 2 |
| 2023 | 17 |
| 2022 | 28 |
| 2021 | 36 |
| 2020 | 39 |