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Airbus;Globes;Hensoldt, 14th European Conference on Synthetic Aperture Radar, EUSAR 2022 -- 25 July 2022 through 27 July 2022 -- 184506, Translational and rotational motion of maneuvering targets can cause range and cross-range cell migrations, culminating in a highly smeared final inverse synthetic aperture radar (ISAR) picture. To overcome this problem, a method for ISAR high-resolution imaging and motion compensation (MOCOMP) is proposed that combines adaptive joint timefrequency (AJTF) analysis and keystone transform (KT) based on genetic algorithm (GA). In synthetic data processing, the motion characteristics of the target are estimated using the Matching Pursuit (MP) technique with a third-order model of polynomial function. The Gabor-wavelet transform (GWT) is utilized as a JTF tool to generate a corresponding 3D time-range-Doppler cube. Keystone transform as remapping of the time axis is applied and Translational Motion Compensation (TMC), Rotational Motion Compensation (RMC), and KT have all been proved to operate well together. In raw data processing, the high-resolution image is obtained by using an AJTF and KT based on a genetic algorithm sans MP and GWT to compensate for migrations in the range and Doppler axis. © 2022 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.

Airbus;Globes;Hensoldt, 14th European Conference on Synthetic Aperture Radar, EUSAR 2022 -- 25 July 2022 through 27 July 2022 -- 184506, Translational and rotational motion of maneuvering targets can cause range and cross-range cell migrations, culminating in a highly smeared final inverse synthetic aperture radar (ISAR) picture. To overcome this problem, a method for ISAR high-resolution imaging and motion compensation (MOCOMP) is proposed that combines adaptive joint timefrequency (AJTF) analysis and keystone transform (KT) based on genetic algorithm (GA). In synthetic data processing, the motion characteristics of the target are estimated using the Matching Pursuit (MP) technique with a third-order model of polynomial function. The Gabor-wavelet transform (GWT) is utilized as a JTF tool to generate a corresponding 3D time-range-Doppler cube. Keystone transform as remapping of the time axis is applied and Translational Motion Compensation (TMC), Rotational Motion Compensation (RMC), and KT have all been proved to operate well together. In raw data processing, the high-resolution image is obtained by using an AJTF and KT based on a genetic algorithm sans MP and GWT to compensate for migrations in the range and Doppler axis. © 2022 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.

The purpose of this work is to test the feasibility of using particle image velocimetry(PIV) for measurements of flow through a porous medium, more specifically in this casea rotating bed reactor S3. The results from experiments preformed can then be usedto validate and improve computational fluid dynamics models. The report presentsdifferent possible combinations of solids and fluids for refractive index matchingand tests some velocity limits of the optical equipment used. PIV appears to be apromising method for measuring flow through a porous medium. The theoreticallimit due to motion blur is an angular velocity of around 3800 RPM, and the actualtested lower bound for this limit is 453 RPM.

The purpose of this work is to test the feasibility of using particle image velocimetry(PIV) for measurements of flow through a porous medium, more specifically in this casea rotating bed reactor S3. The results from experiments preformed can then be usedto validate and improve computational fluid dynamics models. The report presentsdifferent possible combinations of solids and fluids for refractive index matchingand tests some velocity limits of the optical equipment used. PIV appears to be apromising method for measuring flow through a porous medium. The theoreticallimit due to motion blur is an angular velocity of around 3800 RPM, and the actualtested lower bound for this limit is 453 RPM.

We report a study where Car–Parrinello molecular dynamics simulations and variable-temperature (30–300 K) 1H spin–lattice relaxation time experiments nicely complement each other to characterize the dynamics within a set of four crystalline 1,4-diethynylbicyclo[2.2.2]octane (BCO) rotors assembled in the metal–organic rotor, {Li+4(−CO2-Ph-BCO-py)4(H2O)8}·2DMF. The remarkable finding of this work is that, despite the individual rotational barriers of four rotors being indiscernible and superimposed in a broad relaxation process, we were able to unravel a strongly interrelated series of rotational motions involving disrotatory and conrotatory motions in pairs as well as rotational steps of single rotators, all three processes with similar, sizeable rotational barriers of 6 kcal mol−1. It is noteworthy that DFT molecular dynamics simulations and variable-temperature (30–300 K) proton spin–lattice relaxation time experiments deliver the same high value for the rotational barriers stressing the potential of the combined use of the two techniques in understanding rotational motion at the nanoscale.

In some social or religious events, pedestrians make spiral movement circulating around the central object. This paper studies the way making a favourable model to reproduce such a movement. The pedestrian motion is modelled by use of Cellular Automata (CA). The model is implemented in square lattice with static floor fields in polar coordinate. In order to obtain realistic behaviour, we have further implemented the floor field associated to the wall avoidance and lane formation. The results are quantitatively analysed to evaluate the circularity of the pedestrian movement by use of the optical flow analysis, one of the image processing techniques. Velocity vector of the brightness patterns in the simulated movies are evaluated by this approach. The results of various simulations and evaluations show that this model adequately reproduces the spiral movement of pedestrians.

Flow velocity in a Czochralski crystal puller model was measured by an ultrasonic technique. Silicone oil and mercury were used as model liquids and the experiments covered a wide range of Reynolds number Re equal or nearly equal to 10(exp 2)-10(exp 5). From the velocity measurements, oscillatory characteristics of the flow were obtained. Six groups of different frequencies of the oscillation were found to exist in the experiments without applying temperature differences. The influence of thermal convection on frequencies of the oscillation was clarified in the case of mercury. Due to the thermal convection, one frequency of the oscillation is divided into two frequencies. With increasing Reynolds number, the frequencies joined again and a chaotic flow was finally observed., チョクラルスキイ結晶成長法モデルでの流れ速度を超音波を用いた手法で測定した。シリコンオイルと水銀をモデル流体として用い、広い範囲のレイノルズ数Re≒10(exp 2)〜10(exp 5)のもとで実験を行った。速度測定から流れの振動特性が得られ、温度差を与えない実験では異なった振動数の6つのグループが存在することが分かり、また水銀の場合については熱対流の振動数への影響が明らかになった。熱対流により、1つの振動数は2つに分かれ、レイノルズ数の増加につれて、2つの振動数の流れは合流し、カオス流が観測された。

In this paper, we present an improved algorithm for the segmentation of cytoplasm and nuclei from clumps of overlapping cervical cells. This problem is notoriously difficult because of the degree of overlap among cells, the poor contrast of cell cytoplasm and the presence of mucus, blood, and inflammatory cells. Our methodology addresses these issues by utilizing a joint optimization of multiple level set functions, where each function represents a cell within a clump, that have both unary (intracell) and pairwise (intercell) constraints. The unary constraints are based on contour length, edge strength, and cell shape, while the pairwise constraint is computed based on the area of the overlapping regions. In this way, our methodology enables the analysis of nuclei and cytoplasm from both free-lying and overlapping cells. We provide a systematic evaluation of our methodology using a database of over 900 images generated by synthetically overlapping images of free-lying cervical cells, where the number of cells within a clump is varied from 2 to 10 and the overlap coefficient between pairs of cells from 0.1 to 0.5. This quantitative assessment demonstrates that our methodology can successfully segment clumps of up to 10 cells, provided the overlap between pairs of cells is <0.2. Moreover, if the clump consists of three or fewer cells, then our methodology can successfully segment individual cells even when the overlap is ∼0.5. We also evaluate our approach quantitatively and qualitatively on a set of 16 extended depth of field images, where we are able to segment a total of 645 cells, of which only ∼10% are free-lying. Finally, we demonstrate that our method of cell nuclei segmentation is competitive when compared with the current state of the art. © 2015 IEEE.

Flow-induced crystallization is investigated through short-term shear flow experiments on poly(1-butene) in the RheoDSC device. We demonstrate that the DSC signal shows contributions from spherulitic morphology in the center of the sample and oriented structures at the edge of the sample, the latter being induced by edge effects at the free surface. It is shown that, although small in terms of volume, the crystallization at the edge has a dominating influence on the measured rheology. We show how these kinds of effects can be recognized in stand-alone rheometric studies of flow-induced crystallization.

Flow-induced crystallization is investigated through short-term shear flow experiments on poly(1-butene) in the RheoDSC device. We demonstrate that the DSC signal shows contributions from spherulitic morphology in the center of the sample and oriented structures at the edge of the sample, the latter being induced by edge effects at the free surface. It is shown that, although small in terms of volume, the crystallization at the edge has a dominating influence on the measured rheology. We show how these kinds of effects can be recognized in stand-alone rheometric studies of flow-induced crystallization.

This paper describes the basic design of a low-cost boundary layer wind tunnel specially conceived to be much shorter than conventional environmental wind tunnels while allowing for real-time adjustment of vortex size and speed without needing to alter mean flow speed or affecting fan performance. Potential applications include medium scale modeling of atmospheric wind as it interacts with large urban areas, soil erosion, sediment transportation, and large-area pollution dispersion. Also, calibration of some numerical models of two dimensional low-speed fluid flow may be accomplished with adequate instrumentation., Se propone un diseño de bajo costo de un túnel de viento con vórtice variable, que mediante la inyección controlada de flujos cruzados direccionales, permite variar el tamaño y velocidad de rotación de los vórtices independientemente de la velocidad promedio del flujo. Se evita con ello la reconfiguración de la sección de estabilización, comúnmente utilizado en los túneles de capa limite. El uso de este túnel de viento en la escala y velocidad indicada serían para pruebas prácticas usando modelos a escala para cuantificar la interacción del viento atmosférico con construcciones civiles, caracterizar patrones de erosión de terrenos y transporte de sedimentos, y determinar los patrones generales de dispersión de contaminantes atmosféricos en ciertas escalas de terreno; podría utilizarse también para definir parámetros de calibración en modelos numéricos de flujo de fluidos a baja velocidad en dos dimensiones.

This paper describes the basic design of a low-cost boundary layer wind tunnel specially conceived to be much shorter than conventional environmental wind tunnels while allowing for real-time adjustment of vortex size and speed without needing to alter mean flow speed or affecting fan performance. Potential applications include medium scale modeling of atmospheric wind as it interacts with large urban areas, soil erosion, sediment transportation, and large-area pollution dispersion. Also, calibration of some numerical models of two dimensional low-speed fluid flow may be accomplished with adequate instrumentation., Se propone un diseño de bajo costo de un túnel de viento con vórtice variable, que mediante la inyección controlada de flujos cruzados direccionales, permite variar el tamaño y velocidad de rotación de los vórtices independientemente de la velocidad promedio del flujo. Se evita con ello la reconfiguración de la sección de estabilización, comúnmente utilizado en los túneles de capa limite. El uso de este túnel de viento en la escala y velocidad indicada serían para pruebas prácticas usando modelos a escala para cuantificar la interacción del viento atmosférico con construcciones civiles, caracterizar patrones de erosión de terrenos y transporte de sedimentos, y determinar los patrones generales de dispersión de contaminantes atmosféricos en ciertas escalas de terreno; podría utilizarse también para definir parámetros de calibración en modelos numéricos de flujo de fluidos a baja velocidad en dos dimensiones.

The paper introduces a methodology for numerical simulation of landslides experiencing considerable deformations and topological changes. Within an interface capturing approach, all interfaces are implicitly described by specifically defined level-set functions allowing arbitrarily evolving complex topologies. The transient interface evolution is obtained by solving the level-set equation driven by the physical velocity field for all three level-set functions in a block Jacobi approach. The three boundary-coupled fluid-like continua involved are modeled as incompressible, governed by a generalized non-Newtonian material law taking into account capillary pressure at moving fluid-fluid interfaces. The weighted residual formulation of the level-set equations and the fluid equations is discretized with finite elements in space and time using velocity and pressure as unknown variables. Non-smooth solution characteristics are represented by enriched approximations to fluid velocity (weak discontinuity) and fluid pressure (strong discontinuity). Special attention is given to the construction of enriched approximations for elements containing evolving triple junctions. Numerical examples of three-fluid tank sloshing and air-water-liquefied soil landslides demonstrate the potential and applicability of the method in geotechnical investigations. © 2012 John Wiley & Sons, Ltd.

The paper introduces a methodology for numerical simulation of landslides experiencing considerable deformations and topological changes. Within an interface capturing approach, all interfaces are implicitly described by specifically defined level-set functions allowing arbitrarily evolving complex topologies. The transient interface evolution is obtained by solving the level-set equation driven by the physical velocity field for all three level-set functions in a block Jacobi approach. The three boundary-coupled fluid-like continua involved are modeled as incompressible, governed by a generalized non-Newtonian material law taking into account capillary pressure at moving fluid-fluid interfaces. The weighted residual formulation of the level-set equations and the fluid equations is discretized with finite elements in space and time using velocity and pressure as unknown variables. Non-smooth solution characteristics are represented by enriched approximations to fluid velocity (weak discontinuity) and fluid pressure (strong discontinuity). Special attention is given to the construction of enriched approximations for elements containing evolving triple junctions. Numerical examples of three-fluid tank sloshing and air-water-liquefied soil landslides demonstrate the potential and applicability of the method in geotechnical investigations. © 2012 John Wiley & Sons, Ltd.

The dynamics of a 2D rotating Crookes radiometer is studied using a moving mesh unified gas kinetic scheme. The whole evolution process of a fan from an initial unsteady start-up to a final steady state rotational movement in a rarefied gas environment is simulated numerically. Through the numerical study, the unsteady force distribution along a vane which dynamically drives the fan movement is captured. And a quantitative connection between total torque and rotational speed of the fan in the Knudsen number regime of 10-3 < Kn < 102 is obtained. Based on the dimensional analysis, the total radiometric torque can be decomposed into a net radiometric driving torque and a rotational resistance. Based on the numerical data, the analytical functions of the torque and angular velocity of a rotating fan in terms of Knudsen number are quantitatively constructed. This relationship is used to explain the experimental observation of the Knudsen number shift for the appearance of the maximum torque and the maximum rotational speed in the transitional flow regime. (C) 2012 American Institute of Physics. [http://dx.doi.orgt10.1063/1.4765353]

The dynamics of a 2D rotating Crookes radiometer is studied using a moving mesh unified gas kinetic scheme. The whole evolution process of a fan from an initial unsteady start-up to a final steady state rotational movement in a rarefied gas environment is simulated numerically. Through the numerical study, the unsteady force distribution along a vane which dynamically drives the fan movement is captured. And a quantitative connection between total torque and rotational speed of the fan in the Knudsen number regime of 10-3 < Kn < 102 is obtained. Based on the dimensional analysis, the total radiometric torque can be decomposed into a net radiometric driving torque and a rotational resistance. Based on the numerical data, the analytical functions of the torque and angular velocity of a rotating fan in terms of Knudsen number are quantitatively constructed. This relationship is used to explain the experimental observation of the Knudsen number shift for the appearance of the maximum torque and the maximum rotational speed in the transitional flow regime. (C) 2012 American Institute of Physics. [http://dx.doi.orgt10.1063/1.4765353]

The elliptical instability is a generic instability which takes place in any rotating flow whose streamlines are elliptically deformed. Up to now, it has been widely studied in the case of a constant, non-zero differential rotation between the fluid and the elliptical distortion with applications in turbulence, aeronautics, planetology, and astrophysics. In this letter, we extend previous analytical studies and report the first numerical and experimental evidence that elliptical instability can also be driven by libration, i.e., periodic oscillations of the differential rotation between the fluid and the elliptical distortion, with a zero mean value. Our results suggest that intermittent, space-filling turbulence due to this instability can exist in the liquid cores and subsurface oceans of so-called synchronized planets and moons. © 2012 American Institute of Physics.

The elliptical instability is a generic instability which takes place in any rotating flow whose streamlines are elliptically deformed. Up to now, it has been widely studied in the case of a constant, non-zero differential rotation between the fluid and the elliptical distortion with applications in turbulence, aeronautics, planetology, and astrophysics. In this letter, we extend previous analytical studies and report the first numerical and experimental evidence that elliptical instability can also be driven by libration, i.e., periodic oscillations of the differential rotation between the fluid and the elliptical distortion, with a zero mean value. Our results suggest that intermittent, space-filling turbulence due to this instability can exist in the liquid cores and subsurface oceans of so-called synchronized planets and moons. © 2012 American Institute of Physics.

Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 x 10^[4], 2.0 x 10^[5], and 1.14 x 10^[6]. The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.

Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 x 10^[4], 2.0 x 10^[5], and 1.14 x 10^[6]. The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.

The dynamics of a 2D rotating Crookes radiometer is studied using a moving mesh unified gas kinetic scheme. The whole evolution process of a fan from an initial unsteady start-up to a final steady state rotational movement in a rarefied gas environment is simulated numerically. Through the numerical study, the unsteady force distribution along a vane which dynamically drives the fan movement is captured. And a quantitative connection between total torque and rotational speed of the fan in the Knudsen number regime of 10-3 < Kn < 102 is obtained. Based on the dimensional analysis, the total radiometric torque can be decomposed into a net radiometric driving torque and a rotational resistance. Based on the numerical data, the analytical functions of the torque and angular velocity of a rotating fan in terms of Knudsen number are quantitatively constructed. This relationship is used to explain the experimental observation of the Knudsen number shift for the appearance of the maximum torque and the maximum rotational speed in the transitional flow regime. (C) 2012 American Institute of Physics. [http://dx.doi.orgt10.1063/1.4765353]

A complete original study of the linear temporal instability analysis of two viscous and immiscible fluids enclosed in a rigid cylinder rotating about its axis and separated by a cylindrical interface is performed for the case of higher density fluid located in the annulus. The results of the present contribution fill the lack of an overall assessment of the system behavior due to the increase of both the analytical difficulties and the number of the governing parameters when the several physical effects are all included. The analysis is carried out numerically by discretizing the equations of the evolution of disturbances separately in the two phases formulated in a rotating reference frame. Normal mode analysis leads to a generalized eigenvalue problem which is solved by means of a Chebyshev collocation spectral method. The investigation of the preferred modes of instability is carried out over wide ranges of the parameters space. The behavior of the system is physically discussed and is compared to inviscid asymptotic limits and to viscous approximate solutions of the previous literature.

The paper presents the viscoplastic phenomena observed during the rotational friction-welding process of high-speed steel M2 (AISI SAE) with carbon steel 1060 (AISI SAE The structure, phase composition and distribution of the carbide phase in the friction plane and adjoining zones are examined by using optical microscopy (OM) with a system for quantitative analysis, and scanning electron microscopy (SEM) in addition to EDS analysis. The experimentally-checked mathematical relationship is suggested for the calculation of the radial movements of the carbide phase, immediately next to the friction plane. On the basis of qualitative and quantitative evaluation of the microstructural and rheological appearances, a model of carbide phase distribution is also established in the viscoplastic and viscous layers in the area of the friction plane.

The flow in an enclosed rotating cylinder with a stationary lower end wall is investigated numerically. For fast rotation rates, the flow in the interior is primarily in the azimuthal direction, with an angular momentum distribution very close to that corresponding to solid-body rotation for about the inner-half radius. The differential rotation sets up a large-scale circulation that is primarily present in the boundary layers on the rotating top and sidewalls and the stationary bottom wall, with a very weak effusive component throughout the bulk interior providing a matching between the boundary layer flows on the top and bottom. The top end wall boundary layer has a profile that very closely matches the von Kármán solution for a rotating disk boundary layer; it is stable and very robust to finite disturbances for all rotation rates considered. The boundary layer on the stationary bottom end wall has a profile that agrees with the Bödewadt solution for a stationary disk with an ambient flow in solid-body rotation. This boundary layer is not robust, suffering crossflow instability to multiarmed spiral waves via a supercritical Hopf bifurcation, as well as being susceptible to axisymmetric circular waves that travel radially inward where the boundary layer profile is most inflectional. In the absence of any external forcing, the circular waves are transitory, but low amplitude forcing can sustain them indefinitely, whereas the spiral waves are essentially unaffected by the external forcing., Peer Reviewed, Postprint (published version)

The three-dimensional axisymmetry-breaking instability of axisymmetric flow between a rotating lid and a stationary cylinder is analyzed both numerically and experimentally for the case of tall cylinders with the height/radius aspect ratio between 3.3 and 5.5. A complete stability diagram for the primary three-dimensional instability is obtained experimentally and computed numerically. The instability sets in due to different three-dimensional disturbance modes that are characterized by different azimuthal wavenumbers. The critical Reynolds numbers and associated frequencies are identified for each mode. The onset of three-dimensional flow behavior is measured by combining the high spatial resolution of particle image velocimetry and the temporal accuracy of laser Doppler anemometry. The results are compared to the numerical stability analysis. The measured onset of three dimensionality is in a good agreement with the numerical results. Disagreements observed in supercritical regimes can be explained by secondary bifurcations that are not accounted for by linear stability analysis of the primary base flow. ©2009 American Institute of Physics

To study the rotational motion of BH4 tetrahedra in LiBH 4, we have measured the 1H and 11B nuclear magnetic resonance spectra and spin-lattice relaxation rates in this compound over wide ranges of temperature (92-424 K) and resonance frequency (14-90 MHz for 1H and 14-28 MHz for 11B). In the low-temperature (orthorhombic) phase of LiBH4, our spin-lattice relaxation results are consistent with a coexistence of two types of the rotational motion of BH4 tetrahedra with the activation energies of 0.182 ± 0.003 eV and 0.251 ± 0.004 eV. For both types of motions, the jump rates of the reorientations reach the values of the order of 1011 s-1 near the upper limit of the temperature range of the orthorhombic phase stability (T0 ≈381 K). In the high-temperature (hexagonal) phase, both the 1H and 11B spin-lattice relaxation rates are governed by an additional low-frequency fluctuation process (with the characteristic rate of the order of 107 s-1 just above T0) due to the translational diffusion of Li ions. © 2008 American Chemical Society.

SCOPUS: ar.j, info:eu-repo/semantics/published

SCOPUS: ar.j, info:eu-repo/semantics/published

The physical structure and the evolution of helicopter blade tip vortices, particularly the effect of the filament strain and flow rotation effects on the turbulent structure, were investigated through model-scale hovering rotor experiments as well as by developing a mathematical model from the Navier-Stokes (N--S) equations. The flow properties were measured using a high-resolution, three-component Laser Doppler Velocimetry (LDV) system. Images of the tip vortices were also obtained using laser sheet flow visualization. A strain field on the tip vortices was introduced by placing a solid boundary downstream of the rotor. As the vortices approached this boundary, they were convected radially outwards enabling measurements to be obtained in a known strain field. Comparing these measurements with vortex measurements in free-air provided considerable insight into the interdependence of strain and diffusion and their impact on the evolution of rotor tip vortices. The measurements also served to validate a mathematical model developed to predict the core growth of the tip vortices, which included the effects of both filament strain and diffusion. The measurements also laid the groundwork for the development of a comprehensive engineering tip vortex core growth model, which combined the effects of vortex filament strain and Reynolds number effects. Laser sheet flow visualization of the vortex core structure indicated the presence of three distinct regions --- an inner laminar region, an intermediate transition region and an outer turbulent region. Analysis of the velocity profiles measured across the vortex core at various wake ages further supported this hypothesis. The effects of flow rotation on the turbulence present inside the vortex core was quantified based on a Richardson number concept. This results in a laminar flow structure until a particular distance from the vortex center that correlated with the location where the Richardson number fell below a threshold va

Wind flow over topography is often converted to vortex flow due to the interaction of specific features of the terrain such as two mountain peaks. An example of this is found in the area of Straumsfjorden in Northern Norway at certain wind directions. During an emergency flight along that coastline a rescue helicopter of type Eurocopter SA 365N Dolphin 2 experienced a sudden pitch-down change of attitude, which was subsequently corrected by the pilot and the automatic flight control system. After a safe landing the crew observed that both sides of the horizontal stabilizer were missing. Since there were strong winds at the time of the incident, the Norwegian Aircraft Accident Investigation Board ordered a numerical wind analysis of the mountainous area around the pitch-down location. This paper reports on that study and sets forth a hypothesis of dynamic stall together with torsional loading as the cause of the mishap. The physical domain under study is an area of 15 by 20 km and a height of 2 km. This domain was transformed into a numerical space based on a digital representation of the topography. Hence, about 400,000 computational cells were generated in which the non-viscous Euler equations for rotational flow were solved. The numerical method applied is based on the time-stepping finite volume technique and incorporates cell-centered fluxes for spatial discretization. The numerical simulation of steady-state wind conditions revealed strong vortex flow patterns in two areas of the flight path, one coinciding with the location of the sudden nose-down movement of the helicopter and the recovery of the stabilizer in the fjord. This wind flow structure will continue to introduce strong transient flow conditions on flight vehicles and their horizontal stabilizers, including the two vertical fins. This highly 3D wind-induced flow could be the cause for the structural failure of the stabilizer, however, no aerodynamic proof could be put forward. (12 figures, 4 refs7, Also see ADM001490. Presented at the RTO Applied Vehicle Technology (AVT) Panel Symposium held in Loen, Norway, on 7-11 May 2001. Pub. in report number RTO-MP-069(I). The original document contains color images.

The main objectives are not only to develop recommended procedures for control of large scale swirling and secondary flows, but also to extract from empirical observations general concepts which design and test engineers could adapt for 'tailoring and manipulating' their own special flows with different rotational characteristics. Several typical rotational flows were generated and superimposed on the flow through the test section. Careful calibration was carried out using hot-wire anemometers, and miniature vane-vorticity indicators. These flows represent the basic target conditions to be controlled by inserting various flow manipulators: honeycombs, screens and perforated plates. Comparison of the characteristics of the flow downstream of the manipulators (e.g., distribution of streamwise vorticity) to the original test flows provides a measure of the efficacy of the manipulators in suppressing large scale vorticity as well as clues to dominant mechanisms of the flow transformations.

Curved wall diffusers designed by using an inverse method of solution of potential flow theory have been shown to be both short and highly efficient. These features make this type of diffuser attractive in thrust ejector applications. In ejectors, however, the flow at the diffuser inlet is nearly a uniform shear flow. This paper presents a method used in examining the flow velocity along the diffuser wall and some of the analytical results for diffusers designed with potential flow theory and receiving a rotational flow. The inlet flow vorticity and the diffuser area ratios prescribed in the inverse solution of the irrotational flow are the parameters of the study. The geometry of a sample ejector using such a diffuser and its estimated thrust augmentation ratio are also presented. (Author)

This characteristic method for the determination of supersonic phenomena was first used by Prandtl and Busemann for two-dimensional flow. For flow with axial symmetry Frankl used the method of characteristics for determining the shape of a supersonic circular effuser with uniform exit velocity, and Ferrari independently used the characteristics method for determining supersonic phenomena for every type of boundary condition. Subsequently Guderley and Sauer transformed the system proposed by Frankl and Ferrari and obtained a different analytical solution of the problem. In all applications the hypothesis of potential flow was made; therefore the equation of potential flow was used.

Fanaie, V. R., Khiadani, M., & Ayres, T. (2019). Effects of internal geometry on hydrodynamics of dissolved air flotation (DAF) tank: An experimental study using particle image velocimetry (PIV). Colloids and Surfaces A: Physicochemical and Engineering Aspects, 575, 382-390. Available here

Táto diplomová práca sa venuje návrhu obežného kolesa radiálneho odstredivého čerpadla z hľadiska predikcie rýchlostného poľa v meridiálnej rovine. Pri tomto návrhu je využitý software spájajúci potenciálnu a Francisovu metódu predikcie rýchlostného poľa. Výsledkom je 6 návrhov, ktoré reprezentujú obe metódy a zároveň aj ich vzájomné spojenie. Súčasťou práce je aj vlastný návrh geometrie pomocou základných empirických vzťahov. Všetky tieto návrhy sú následne porovnané medzi sebou a zároveň aj s originálnou geometriou čerpadla ktoré má n_s=135,36 min^(-1). Pri vyhodnotení je najväčší dôraz kladený na porovnanie predikcií rýchlostného poľa meridiánom s CFD simuláciami. A to hlavne ako dobre sa predikcie zhodujú so simuláciami, ako sa odlišujú a aký vplyv má konečný počet lopatiek, ich nenulová hrúbka a ďalšie faktory na výsledné rýchlostné pole., This master´s thesis deals with the design of impeller of radial centrifugal pump from the point of view of prediction of velocity field in meridional plane. To achieve this, a software combining potential flow method with Francis’s method of velocity field prediction was used. This results to 6 designs, which represent both methods and simultaneously a combination of both. Also, an own design is proposed using basic empirical relations. All this design proposals are then compared with each other and with original geometry of radial pump with n_s=135,36 min^(-1).When evaluating results, greatest emphasis is placed on comparison of predicted velocity field with the one obtained by using CFD simulations. And how well the prediction stacks up to the simulations and how the finite number of blades, their thickness and other factors affects resulting velocity field.