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81
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Boundary Layer on the Flat Plate with Roughness Strip
Skála, Vladislav
2021 - English
Effect of the roughness strip on the boundary layer development on a flat plate was studied experimentally. A special model of a flat plate was designed. Experiment was made in non perturbed flow. Smooth flat plate (with super elliptical leading edge) was equipped with short roughness strip (close to the leading edge). Profiles of total pressure along the boundary layer were measured using flattened Pitot tube. First basic results of experiments are presented.
Keywords:
boundary layer; transition to turbulence; roughness strip
Fulltext is available at external website.
Boundary Layer on the Flat Plate with Roughness Strip
Effect of the roughness strip on the boundary layer development on a flat plate was studied experimentally. A special model of a flat plate was designed. Experiment was made in non perturbed flow. ...
CFD Analysis of Flow in a Blade Cascade Deformed Due to Forced Torsional Vibration
Vomáčko, V.; Šidlof, P.; Šimurda, David; Hála, Jindřich
2021 - English
The paper presents a 3D numerical simulation of flow in a blade cascade, whose geometry models the test section of a new experimental facility for blade flutter research. In the experimental setup, the middle blade of the cascade undergoes high-frequency forced sinusoidal pitching oscillation. Due to inertial forces, the slender blade deforms elastically to certain degree. The goal of this study is to assess the influence of the elastic deformation on the flow field. To compute the deformed geometry, a transient structural analysis was performed. In the second part, the CFD model of flow past a 3D blade cascade with deformed and undeformed blade is presented and these two configurations are compared. For the deformed configuration the incidence angle increases along the blade span from -1.8° to -2.7°. However, the Mach number distribution along the span varies less than expected. blade cascade, flutter, turbomachinery, CFD
Keywords:
blade cascade; flutter; turbomachinery; CFD
Fulltext is available at external website.
CFD Analysis of Flow in a Blade Cascade Deformed Due to Forced Torsional Vibration
The paper presents a 3D numerical simulation of flow in a blade cascade, whose geometry models the test section of a new experimental facility for blade flutter research. In the experimental setup, ...
Macroscopic constitutive model for NiTi shape memory alloys: Formulation, numerical imple-mentation, and application in materials research
Frost, Miroslav; Sedlák, Petr
2021 - English
In this contribution, we present a constitutive model for shape memory alloys formulated within the generalized standard materials framework. It provides substantial flexibility for the development of constitutive equations. On the other hand, finding the optimal numerical solution procedure for the resulting systems of evolutionary inclusions can be challenging. We present our approach and illustrate the capabilities of the model on several numerical simulations compared with experiments.
Keywords:
shape memory alloys; modeling
Fulltext is available at external website.
Macroscopic constitutive model for NiTi shape memory alloys: Formulation, numerical imple-mentation, and application in materials research
In this contribution, we present a constitutive model for shape memory alloys formulated within the generalized standard materials framework. It provides substantial flexibility for the development of ...
Comparison of Transonic Flows Through Two Tip-Section Turbine Blade Cascades with Different Flat Profiles
Musil, Josef; Příhoda, Jaromír; Fürst, J.; Luxa, Martin; Šimurda, David
2021 - English
The contribution deals with numerical simulations of 2D compressible flow through two variants of the tip-section turbine blade cascade with a flat profile for the subsonic inlet. Simulations were realised by means of the OpenFOAM code using the γ-Reθ bypass transition model completed by the two-equation SST turbulence model. Predictions were focused particularly on the impact of the shock-wave/boundary-layer interaction on the flow structure in the inter-blade channel. Beside the effect of the inlet angle on the flow around the leading edge was studied. Numerical results were compared with optical and pressure experimental data.
Keywords:
supersonic tip-section blade cascade; CFD; transition modelling
Fulltext is available at external website.
Comparison of Transonic Flows Through Two Tip-Section Turbine Blade Cascades with Different Flat Profiles
The contribution deals with numerical simulations of 2D compressible flow through two variants of the tip-section turbine blade cascade with a flat profile for the subsonic inlet. Simulations were ...
Spectral/hp elements in fluid structure interaction.
Pech, Jan
2021 - English
This work presents simulations of incompressible fluid flow interacting with a moving rigid body. A numerical algorithm for incompressible Navier-Stokes equations in a general coordinate system is applied to two types of body motion, prescribed and flow-induced. Discretization in spatial coordinates is based on the spectral/hp element method. Specific techniques of stabilisation, mesh design and approximation quality estimates are described and compared. Presented data show performance of the solver for various geometries in 2D from slowly moving cylinder to high speed flow around aerodynamic profiles.
Keywords:
spectral/hp element method; fluid structure interaction; spectral vanishing viscosity
Fulltext is available at external website.
Spectral/hp elements in fluid structure interaction.
This work presents simulations of incompressible fluid flow interacting with a moving rigid body. A numerical algorithm for incompressible Navier-Stokes equations in a general coordinate system is ...
On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2020 - English
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of statistic quantities along the cylinder is uniform, and i.e. 2D, the instantaneous flow structure is fully 3D. Within the velocity fluctuating flow field the structures containing streamwise vorticity and velocity components are dominant. The POD modes connected with von Kármán vortex street are identified.
Keywords:
circular cylinder; wake; 3D structure; POD
Fulltext is available at external website.
On the 3D Dynamics of the Wake Behind a Circular Cylinder
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of ...
Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
Pech, Jan
2020 - English
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution to the Navier-Stokes and Navier-Stokes-Fourier system. Reynolds numbers are considered in range 100-20000, ratio of cylinder-wall and upstream temperature is up to 1.5. Curves representing evolution of separation positions in time provide novel insight to vortex formation. Various regimes are recognized and some of them can be assigned to phenomena described formerly in experiment.
Keywords:
transition to turbulence; heated flow; cylinder flow; separation angle; Navier-Stokes- Fourier; spectral/hp element method
Fulltext is available at external website.
Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution ...
On Harmonic Content of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.
2020 - English
The wake behind cylinder of circular cross-section is subjected to detailed analysis from the point of view harmonic content. The basic, fundamental frequency could be linked to well-known Bénard-von Kámán vortex street, it is called Strouhal frequency very often. However higher harmonics of 2nd and 3rd order have been detected, as well as important inharmonic partials. The topologies of the velocity flow-field corresponding to the harmonic is to be shown.
Keywords:
circular cylinder; wake; Strouhal number; higher harmonics; oscillation pattern decomposition
Fulltext is available at external website.
On Harmonic Content of the Wake Behind a Circular Cylinder
The wake behind cylinder of circular cross-section is subjected to detailed analysis from the point of view harmonic content. The basic, fundamental frequency could be linked to well-known Bénard-von ...
POD-DEIM-based model order reduction for four-way coupled fluid-solid flows
Isoz, Martin; Šourek, M.
2020 - English
Proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM) have become established tools for model order reduction in simulations of fluid flows. However, including moving solid bodies in the computational domain poses additional issues with respect to the fluid-solid coupling and to the solution of the movement of the solids. Still, it seems that if the hybrid ctitious domain-immersed boundary method is used to include the solids in the flow domain, POD-DEIM based approaches may be extended for four-way coupled particleladen flows. The present work focuses on the construction of POD-DEIM based reduced order models for the aforementioned flows.
Keywords:
CFD; POD; DEIM; HFDIB-DEM; OpenFOAM
Fulltext is available at external website.
POD-DEIM-based model order reduction for four-way coupled fluid-solid flows
Proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM) have become established tools for model order reduction in simulations of fluid flows. However, including ...
Three-dimensional numerical analysis of Czech vowel production
Hájek, P.; Švancara, P.; Horáček, Jaromír; Švec, J. G.
2020 - English
Spatial air pressures generated in human vocal tract by vibrating vocal folds present sound sources of vowel production. This paper simulates phonation phenomena by using fluid-structure-acoustic scheme in a three-dimensional (3D) finite element model of a Czech vowel [o:]. The computational model was composed of four-layered M5-shaped vocal folds together with an idealized trachea and vocal tract. Spatial fluid flow in the trachea and in the vocal tract was obtained by unsteady viscous compressible Navier-Stokes equations. The oscillating vocal folds were modelled by a momentum equation. Large deformations were allowed. Transient analysis was performed based on separate structure and fluid solvers, which were exchanging loads acting on the vocal folds boundaries in each time iteration. The deformation of the fluid mesh during the vocal fold oscillation was realized by the arbitrary Lagrangian-Eulerian approach and by interpolation of fluid results on the deformed fluid mesh. Preliminary results show vibration characteristics of the vocal folds, which correspond to those obtained from human phonation at higher pitch. The vocal folds were self-oscillating at a reasonable frequency of 180 Hz. The vocal tract eigenfrequencies were in the ranges of the formant frequencies of Czech vowel [o:] measured on humans, during self-oscillations the formants shifted to lower frequencies.
Keywords:
simulation of phonation; fluid-structure-acoustic interaction; compressible flow; finite element method; biomechanics of voice
Fulltext is available at external website.
Three-dimensional numerical analysis of Czech vowel production
Spatial air pressures generated in human vocal tract by vibrating vocal folds present sound sources of vowel production. This paper simulates phonation phenomena by using fluid-structure-acoustic ...
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