scholarly journals Experimental Study of a Normal Shock/Homogeneous Turbulence Interaction

2002 ◽  
Author(s):  
Bruno Auvity ◽  
Ste´phane Barre ◽  
Jean-Paul Bonnet
Keyword(s):  
Supersonic Flow ◽  
Initial Conditions ◽  
Flow Direction ◽  
Normal Shock ◽  
Supersonic Wind Tunnel ◽  
Generator System ◽  
Experimental Realization ◽  
Shock Generator ◽  
Set Up ◽  
Turbulence Generator

The problem of shock wave–turbulence interaction is addressed experimentally in a simplified flow configuration: the shock is normal to the flow direction and the incoming turbulence is homogeneous and quasi-isotropic. This paper mainly deals with the problem of the experimental realization of such an interaction in a supersonic wind tunnel. On the basis of an experimental set-up that showed great aptitude in creating a shock-turbulence interaction pure from major parasitic effects, see Barre et al. (1996), a new turbulence generator and a new shock generator were designed and built. It was found that the new turbulence generator creates a homogenous and quasi-isotropic turbulent supersonic flow at a distance of about 25 mesh sizes. The benefit of this new system was to increase the turbulence level before the interaction with the shock from 0.3% to 1.7%. The new shock generator system permitted to stabilize a normal shock of larger size compared to the previous configuration, at a distance of 32 mesh sizes. Initial conditions at the shock position were determined with details: important turbulent quantities of the supersonic flow before the interaction, such as turbulent kinetic energy, dissipation rate, Taylor micro-scale and integral length scale, were estimated. With this new experimental set-up, detailed turbulence measurements before and after the shock using fluctuations diagram techniques will be performed.

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

Numerical investigations on the hydrogen jet pressure variations in a strut based scramjet combustor

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Jeyakumar Suppandipillai ◽  
Jayaraman Kandasamy ◽  
R. Sivakumar ◽  
Mehmet Karaca ◽  
Karthik K.
Keyword(s):  
Shock Wave ◽  
Supersonic Flow ◽  
Pressure Loss ◽  
Total Pressure ◽  
Injection Pressure ◽  
Total Pressure Loss ◽  
Normal Shock ◽  
Content Type ◽  
Normal Shock Wave ◽  
Scramjet Combustor

Purpose This paper aims to study the influences of hydrogen jet pressure on flow features of a strut-based injector in a scramjet combustor under-reacting cases are numerically investigated in this study. Design/methodology/approach The numerical analysis is carried out using Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport k-ω turbulence model in contention to comprehend the flow physics during scramjet combustion. The three major parameters such as the shock wave pattern, wall pressures and static temperature across the combustor are validated with the reported experiments. The results comply with the range, indicating the adopted simulation method can be extended for other investigations as well. The supersonic flow characteristics are determined based on the flow properties, combustion efficiency and total pressure loss. Findings The results revealed that the augmentation of hydrogen jet pressure via variation in flame features increases the static pressure in the vicinity of the strut and destabilize the normal shock wave position. Indeed, the pressure of the mainstream flow drives the shock wave toward the upstream direction. The study perceived that once the hydrogen jet pressure is reached 4 bar, the incoming flow attains a subsonic state due to the movement of normal shock wave ahead of the strut. It is noticed that the increase in hydrogen jet pressure in the supersonic flow field improves the jet penetration rate in the lateral direction of the flow and also increases the total pressure loss as compared with the baseline injection pressure condition. Practical implications The outcome of this research provides the influence of fuel injection pressure variations in the supersonic combustion phenomenon of hypersonic vehicles. Originality/value This paper substantiates the effect of increasing hydrogen jet pressure in the reacting supersonic airstream on the performance of a scramjet combustor.

Modeling and prediction for the oxidation efficiency of magnesium sulfite in aeration tank of magnesium-based seawater exhaust gas clean system

2017 ◽  
Vol 233 (1) ◽  
pp. 164-173
Author(s):  
Quan Liu ◽  
Yimin Zhu ◽  
Tie Li ◽  
Xiaojia Tang ◽  
Weifeng Liu ◽  
...  
Keyword(s):  
Flow Field ◽  
Initial Conditions ◽  
Negative Impact ◽  
Fluid Model ◽  
Aeration Tank ◽  
Exhaust Gas ◽  
Clean System ◽  
Physics Modeling ◽  
Set Up ◽  
Oxidation Efficiency

In magnesium-based seawater exhaust gas clean system, the desulfurization by-product, magnesium sulfite (MgSO3), has a negative impact on the ecological environment, which needs to be treated to make harmless. Due to the limited space on board, the aeration oxidation method is used to convert it to magnesium sulfate. Because of the variable size, shape and flow field of aeration tank, it is difficult and expensive to design and verify the oxidation efficiency of the aeration tank by experimental method. In this work, in order to predict the oxidation efficiency accurately, RFlow, a computational fluid dynamics software, was used to analyze the flow field and MgSO3 oxidation reaction in aeration tank. The subdomain technology was adopted for physics modeling and mesh generation of the aeration tank, and the total number of meshes was 285,000. The multi-phase flow field model was set up using the multi-fluid model and dispersive k-ε turbulence model. Under the given initial conditions, the predicted oxidation efficiency was 94.2%. Compared with the results of the actual ship test, the prediction model for MgSO3 oxidation efficiency of the aeration tank is reliable.

Improvement of Surface Morphology by Solution Flow Control in Solution Growth of SiC on Off-Axis Seeds

2015 ◽  
Vol 821-823 ◽  
pp. 31-34 ◽  
Author(s):  
Tomonori Umezaki ◽  
Daiki Koike ◽  
S. Harada ◽  
Toru Ujihara
Keyword(s):  
Flow Direction ◽  
Seed Crystal ◽  
Solution Growth ◽  
Rotational Axis ◽  
Solution Flow ◽  
Step Flow ◽  
Unidirectional Flow ◽  
Novel Method ◽  
Set Up ◽  
Top Seeded Solution Growth

The solution growth of SiC on an off-axis seed is effective on the reduction of threading dislocations. We proposed a novel method to grow a SiC crystal on an off-axis seed by top-seeded solution growth (TSSG). In our previous study, a unidirectional solution flow above a seed crystal is effective to suppress surface roughness in the growth on the off-axis seed. However, it is difficult to apply the unidirectional flow in an axisymmetric TSSG set-up. In this study, the unidirectional flow could be achieved by shifting the rotational axis away from the center of the seed crystal. As a result, the smooth surface was obtained in the wider area where the solution flow direction was opposite to the step-flow direction.

Effects of inertia and stratification in incompressible ideal fluids: pressure imbalances by rigid confinement

2013 ◽  
Vol 726 ◽  
pp. 404-438 ◽  
Author(s):  
R. Camassa ◽  
S. Chen ◽  
G. Falqui ◽  
G. Ortenzi ◽  
M. Pedroni
Keyword(s):  
Euler Equations ◽  
Initial Conditions ◽  
Numerical Algorithms ◽  
Wave Dispersion ◽  
Variable Density ◽  
Density Variation ◽  
Fluid Inertia ◽  
Time Dynamics ◽  
Long Wave ◽  
Set Up

AbstractConsequences of density stratification are studied for an ideal (Euler) incompressible fluid, confined to move under gravity between rigid lids but otherwise free to move along horizontal directions. Initial conditions that generate horizontal pressure imbalances in a laterally unbounded domain are examined. The aim is to show analytically the existence of classes of initial data for which total horizontal momentum evolves in time, even though only vertical forces act on the fluid in this set-up. A simple class of such initial conditions, leading to momentum evolution, is identified by systematic asymptotic expansions of the governing inhomogeneous Euler equations in the small-density-variation limit. These results for Euler equations are compared and confirmed with long-wave asymptotic models, which can handle arbitrary density variations and provide closed-form mathematical expressions for limiting cases. In particular, the role of wave dispersion arising from the fluid inertia is captured by the long-wave models, even for short-time dynamics emanating from initial conditions outside the models’ asymptotic range of validity. These results are compared with direct numerical simulations for variable-density Euler fluids, which further validate the numerical algorithms and the analysis.

scholarly journals The non-modal onset of the tearing instability

2018 ◽  
Vol 84 (5) ◽  
Author(s):  
D. MacTaggart
Keyword(s):  
Initial Conditions ◽  
Linear Equations ◽  
Initial Perturbation ◽  
Transient Growth ◽  
Tearing Mode ◽  
Eigenvalue Spectrum ◽  
Tearing Instability ◽  
Set Up ◽  
Solution Behaviour ◽  
Physical Quantities

We investigate the onset of the classical magnetohydrodynamic (MHD) tearing instability (TI) and focus on non-modal (transient) growth rather than the tearing mode. With the help of pseudospectral theory, the operators of the linear equations are shown to be highly non-normal, resulting in the possibility of significant transient growth at the onset of the TI. This possibility increases as the Lundquist number$S$increases. In particular, we find evidence, numerically, that the maximum possible transient growth, measured in the$L_{2}$-norm, for the classical set-up of current sheets unstable to the TI, scales as$O(S^{1/4})$on time scales of$O(S^{1/4})$for$S\gg 1$. This behaviour is much faster than the time scale$O(S^{1/2})$when the solution behaviour is dominated by the tearing mode. The size of transient growth obtained is dependent on the form of the initial perturbation. Optimal initial conditions for the maximum possible transient growth are determined, which take the form of wave packets and can be thought of as noise concentrated at the current sheet. We also examine how the structure of the eigenvalue spectrum relates to physical quantities.

Role of initial condition and parametric uncertainty in a severe hailstorm forecast

2021 ◽  
Author(s):  
Patrick Kuntze ◽  
Annette Miltenberger ◽  
Corinna Hoose ◽  
Michael Kunz
Keyword(s):  
Initial Conditions ◽  
Weather Prediction ◽  
Parametric Uncertainty ◽  
Radar Data ◽  
Cloud Microphysics ◽  
Initial Condition ◽  
Relative Contribution ◽  
Cloud Properties ◽  
Set Up ◽  
The Impact

<p>Forecasting high impact weather events is a major challenge for numerical weather prediction. Initial condition uncertainty plays a major role but so potentially do uncertainties arising from the representation of physical processes, e.g. cloud microphysics. In this project, we investigate the impact of these uncertainties for the forecast of cloud properties, precipitation and hail of a selected severe convective storm over South-Eastern Germany.<br>To investigate the joint impact of initial condition and parametric uncertainty a large ensemble including perturbed initial conditions and systematic variations in several cloud microphysical parameters is conducted with the ICON model (at 1 km grid-spacing). The comparison of the baseline, unperturbed simulation to satellite, radiosonde, and radar data shows that the model reproduces the key features of the storm and its evolution. In particular also substantial hail precipitation at the surface is predicted. Here, we will present first results including the simulation set-up, the evaluation of the baseline simulation, and the variability of hail forecasts from the ensemble simulation.<br>In a later stage of the project we aim to assess the relative contribution of the introduced model variations to changes in the microphysical evolution of the storm and to the fore- cast uncertainty in larger-scale meteorological conditions.</p>

scholarly journals Parametric Study of Tsunamis Generated by Earthquakes and Landslides

2019 ◽  
Vol 7 (5) ◽  
pp. 154 ◽  
Author(s):  
Natalia Perez del Postigo Prieto ◽  
Alison Raby ◽  
Colin Whittaker ◽  
Sarah J. Boulton
Keyword(s):  
Predictive Models ◽  
Initial Conditions ◽  
Quality Data ◽  
Tsunami Generation ◽  
Fault Rupture ◽  
Physical Experiments ◽  
Dual Source ◽  
Set Up ◽  
Displacement Scale ◽  
The University

Tsunami generation and propagation mechanisms need to be clearly understood in order to inform predictive models and improve coastal community preparedness. Physical experiments, supported by mathematical models, can potentially provide valuable input data for standard predictive models of tsunami generation and propagation. A unique experimental set-up has been developed to reproduce a coupled-source tsunami generation mechanism: a two-dimensional underwater fault rupture followed by a submarine landslide. The test rig was located in a 20 m flume in the COAST laboratory at the University of Plymouth. The aim of the experiments is to provide quality data for developing a parametrisation of the initial conditions for tsunami generation processes which are triggered by a dual-source. During the test programme, the water depth and the landslide density were varied. The position of the landslide model was tracked and the free surface elevation of the water body was measured. Hence the generated wave characteristics were determined. For a coupled-source scenario, the generated wave is crest led, followed by a trough of smaller amplitude decreasing steadily as it propagates along the flume. The crest amplitude was shown to be influenced by the fault rupture displacement scale, whereas the trough was influenced by the landslide’s relative density.

Experimentally Measured Boundary and Initial Conditions for Simulations

2014 ◽  
Vol 1041 ◽  
pp. 293-296 ◽  
Author(s):  
Dušan Katunský ◽  
Marek Zozulák ◽  
Marián Vertaľ ◽  
Jozef Šimiček
Keyword(s):  
Boundary Conditions ◽  
Indoor Environment ◽  
Initial Conditions ◽  
Weather Data ◽  
Initial Condition ◽  
Dynamic Boundary Conditions ◽  
Climate Monitoring ◽  
Set Up ◽  
Water Profile

Real dynamic boundary conditions and initial condition has to be taken into an account when simulations need to be done. The most helpful are in situ measurement facilities with climate monitoring. Indoor environment operation modes with different air temperature and relative humidity made indoor boundary conditions. Measured weather data are used to create complete boundary conditions for the research locality. Initial condition of masonry water profile is set up. The initial and boundary conditions are considered for an individual locality simulation proposes.

scholarly journals Mathematical Models with Buckling and Contact Phenomena for Elastic Plates: A Review

Mathematics ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 566
Author(s):  
Aliki D. Muradova ◽  
Georgios E. Stavroulakis
Keyword(s):  
Mathematical Models ◽  
Initial Conditions ◽  
Nonlinear Partial Differential Equations ◽  
Composite Plates ◽  
Contact Problems ◽  
Elastic Plates ◽  
Advantages And Disadvantages ◽  
Contact Models ◽  
Set Up ◽  
Unilateral Contact Problems

A review of mathematical models for elastic plates with buckling and contact phenomena is provided. The state of the art in this domain is presented. Buckling effects are discussed on an example of a system of nonlinear partial differential equations, describing large deflections of the plate. Unilateral contact problems with buckling, including models for plates, resting on elastic foundations, and contact models for delaminated composite plates, are formulated. Dynamic nonlinear equations for elastic plates, which possess buckling and contact effects are also presented. Most commonly used boundary and initial conditions are set up. The advantages and disadvantages of analytical, semi-analytical, and numerical techniques for the buckling and contact problems are discussed. The corresponding references are given.

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