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Aspects of Dosage from Short and Long Duration Emissions
Robins, A.; Hayden, P.; Gallacher, D.; Pace, S.; Chaloupecká, Hana
2022 - English
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop scaling rules that reduce the results to a universal form. The experiments were carried out in the EnFlo meteorological wind tunnel at the University of Surrey. Ensembles of between 100 and 200\nrepeat emissions were used, emission durations between 0.067 and 1.02s and a reference flow speed of 2ms-1. The fetch studied extended to about six source heights downwind (about two boundary layer depths). The structure of the evolving clouds was analysed to determine time of flight, along-wind spread and dosage and to compare the dosage behaviour with the concentration field in a plume from the same source. This illustrated how the two were related and how cloud dosage statistics (mean and\nstandard deviation) could be derived from plume data. It also demonstrated that much larger ensembles were required to reduce the statistical uncertainty in the mean cloud properties. The next steps involve testing these conclusions in a wider range of flow and dispersion conditions, in the presence of obstacles or complex urban areas.
Keywords:
wind tunnel; dose; dosage; gas releases
Available at various institutes of the ASCR
Aspects of Dosage from Short and Long Duration Emissions
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop ...
Simple Rheoscopic Flows Used in Teaching Fluid Mechanics
Duda, D.; Yanovych, Vitalii; Uruba, Václav
2022 - English
Four simple demonstration experiments are presented. They are used as a support in the teaching of Fluid Mechanics I (a compulsory lecture at the University of West Bohemia in Pilsen). All mentioned experiments use the rheoscopic fluid obtained as a water solution of mica powder to visualize the flow in a esthetic way, which, as we hope, has a potential to attract students attention. The experiments are: demonstration of Bernoulli equation in a widening and narrowing channel, Taylor-Couette flow, the effect of viscosity to the scales and decay of turbulence, and the Galilean transformation inside an axial compressor.
Keywords:
teaching; fluid mechanics; demonstration experiment; rheoscopic fluid; Bernoulli equation; Taylor-Couette flow; axial compressor
Fulltext is available at external website.
Simple Rheoscopic Flows Used in Teaching Fluid Mechanics
Four simple demonstration experiments are presented. They are used as a support in the teaching of Fluid Mechanics I (a compulsory lecture at the University of West Bohemia in Pilsen). All mentioned ...
Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii; Duda, D.; Uruba, Václav; Procházka, Pavel P.; Antoš, Pavel
2022 - English
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
Keywords:
roughened cylinder; Strouhal number; spectral distribution; turbulence structure; Hot-wire anemometry
Fulltext is available at external website.
Effect of Cylinder Roughness on Strouhal Number
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics ...
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Pešek, Luděk; Šnábl, Pavel; Prasad, Chandra Shekhar; Delanney, Y.
2022 - English
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in the Institute of Thermomechanics, of CAS, in Prague. These experiments are aimed at stability evaluation of the cascade at running waves or at stability limit testing by flow speed changes or by force impulses of blades. The onset of flutter and its spreading in the cascade are observed, too. The linear cascade model consists of five NACA010 blades. All the blades can be separately excited with electromagnetic torque excitation mechanism and all of them are instrumented to measure the aerodynamic moments which can be used to calculate the aerodynamic work. A more details about the linear blade cascade experimental set up can be found in [1-2]. To predict a dynamic behaviour in the blade cascade, we have been dealing with simplified theoretical modelling of the aeroelastic instability in turbine blade cascade [3-5]. Due to the application of the reduced cascade model consisting of simple elements – springs, rigid bodies, linear dampers – and aeroelastic forces introduced by analytical Van der Pol model, it facilitates to study the dangerous states of vibration of such complicated turbine parts [6-9]. This study is aimed at examination of aeroelastic instabilities of 10-blade cascade at running excitation that arises due to the wakes flowing from stator the blades to the rotating blades. They cause forced excitation in the narrow frequency range.
Keywords:
rotary test; structural dynamics; bladed wheels
Available at various institutes of the ASCR
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in ...
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Košina, Jan; Geneid, A.; Laukkanen, A. M.
2022 - English
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further development of mathematical modelling of phonation. The measurements of the damping ratio, based on high-speed videolaryngoscopic registrations, were realized in vivo on a male subject and in vitro using an originally developed silicon replica of the human vocal folds. In both cases the results show remarkable decrease of vibration frequency of the vocal folds and increase of damping ratio D in the phonation offset limiting to the values D=0.12 in vivo measurement and D=0.11 in vitro measurement. The results for vocal folds’ damping are in good agreement with previous measurements performed in humans using different methods.
Keywords:
phonation offset; high-speed videolaryngoscopy
Available at various institutes of the ASCR
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further ...
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
Zolotarev, Igor; Bula, Vítězslav; Šnábl, Pavel; Snížek, Jan; Souček, Jan
2022 - English
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental investigation.
Keywords:
modal analysis; natural frequencies; modes of vibration
Available at various institutes of the ASCR
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental ...
Identification of material constants of rubber damping segments by modal analysis for railway rubber-resilient wheels
Šulc, Petr; Šnábl, Pavel; Pešek, Luděk; Bula, Vítězslav
2022 - English
In this paper, an experimental and numerical modal analysis is described to assess two rubber compounds for the damping segments of a railway wheel. The subject of this comparison is materiál parameters such as Young’s modulus and loss factor for both compounds in the frequency range up to 6.5 kHz. From this comparison, an idea of the damping, stiffness and durability of these rubber segment materials inside these wheels is obtained.
Keywords:
modal analysis; rubber; railway wheel; damping segment
Available at various institutes of the ASCR
Identification of material constants of rubber damping segments by modal analysis for railway rubber-resilient wheels
In this paper, an experimental and numerical modal analysis is described to assess two rubber compounds for the damping segments of a railway wheel. The subject of this comparison is materiál ...
A parallel algorithm for flux-based bounded scalar Re-distribution
Isoz, Martin; Plachá, M.
2022 - English
Let us assume a bounded scalar function ? : Q = I × ? ? ?0, 1?, I ? R, ? ? R3, where Q is an open bounded domain and its discrete counterpart ?h defined on a computational mesh Qh = Ih × ?h. The problem of redistribution of ?h over ?h ensuring the scalar boundedness while maintaining the invariance of R ?h ?h dV is surprisingly frequent within the field of computational fluid dynamics (CFD). The present contribution is motivated by the case arising from coupling Lagrangian particle tracking and particle deposition within ? h with Eulerian CFD computation. We propose an algorithm for ?h redistribution that is (i) based on fluxes over the computational cells faces, i.e. suitable for finite volume (FV) computations, (ii) localized, meaning that a cell ?h P with ?hP > 1 affects only its closest neighbors with ?h < 1, and (iii) designed for parallel computations leveraging the standard domain decomposition methods.
Keywords:
CFD; OpenFOAM; scalar redistribution
Fulltext is available at external website.
A parallel algorithm for flux-based bounded scalar Re-distribution
Let us assume a bounded scalar function ? : Q = I × ? ? ?0, 1?, I ? R, ? ? R3, where Q is an open bounded domain and its discrete counterpart ?h defined on a computational mesh Qh = Ih × ?h. The ...
Octree-generated virtual mesh for improved contact resolution in CFD-Dem coupling
Studeník, O.; Kotouč Šourek, M.; Isoz, Martin
2022 - English
The present work is focused on improving the efficiency of a computational fluid dynamics (CFD) – discrete element method (DEM) solver allowing for computations with non-spherical solids. In general, the combination of CFD and DEM allows for simulations of freely moving solid particles within a computational domain containing fluid. The standard approach of CFD-DEM solvers is to approximate solid bodies by spheres, the geometry of which can be fully defined via its radius and center position. Consequently, the standard DEM contact models are based on an overlap depth between particles, which can be easily evaluated for a sphere-sphere contact. However, for a contact between two non-spherical particles, the overlap depth cannot be used and has to be replaced by the more general overlap volume. The precision of the overlap volume computation is (i) crucial for the correct evaluation of contact forces, and (ii) directly dependent on the computational mesh resolution. Still, the contact volume evaluation in DEM for arbitrarily shaped bodies is usually by at least one order of magnitude more demanding on the mesh resolution than the CFD. In order to improve the computational efficiency of our CFD-DEM solver, we introduce the concept of an OCTREEbased virtual mesh, in which the DEM spatial discretization is adaptively refined while the CFD mesh remains unchanged.
Keywords:
HFDIB-DEM; CFD; DEM; washcoating; OpenFOAM
Fulltext is available at external website.
Octree-generated virtual mesh for improved contact resolution in CFD-Dem coupling
The present work is focused on improving the efficiency of a computational fluid dynamics (CFD) – discrete element method (DEM) solver allowing for computations with non-spherical solids. In general, ...
Investigation of Transonic Flow through Linear Cascade with Single Blade Incidence Angle Offset
Fürst, J.; Musil, Josef; Šimurda, David
2022 - English
The contribution deals with numerical and experimental investigation of the effect of incidence angle offset in a two-dimensional section of a flat linear blade cascade in a high-speed wind tunnel. The aim of the work is to complement ongoing research of quasi-stationary approximation of aerodynamic flutter by examination of setups leading to transonic flow regimes. The numerical simulations were realized by finite-volume, in-house code developed on top of the open-source software package OpenFOAM. The experiments were conducted in correspondence with the setting of numerical simulations. The comparison of experimental and numerical data is presented on the isentropic Mach number distributions at various locations in the blade cascade. The description of transonic flow structures in the vicinity of blades is also provided.
Keywords:
compressor cascade; flutter; CFD; finite volumes; experimental validation; transonic
Fulltext is available at external website.
Investigation of Transonic Flow through Linear Cascade with Single Blade Incidence Angle Offset
The contribution deals with numerical and experimental investigation of the effect of incidence angle offset in a two-dimensional section of a flat linear blade cascade in a high-speed wind tunnel. ...
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