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The stability properties of basic states are often elucidated by examining the evolution of small disturbances. Such studies have recently been successfully applied to mean turbulent states, obtained through averaging of experimental measurements or Large-Eddy Simulations (LES), for both wall-bounded as well as free shear flows. Typically, the equations are employed using the disturbance form of the equations. To circumvent the necessity to linearize the governing equations, an especially tedious task for viscous and turbulent closure terms, Touber and Sandham (2009) [21], proposed an approach that achieves the same purpose by solving the full Navier-Stokes (NS) equations, with a forcing term to maintain mean flow invariance. The method places no restrictions, such as slow streamwise variations, on the underlying basic state. The goals of the current work are to first verify this mean flow perturbation (NS-MFP) technique and then apply it to the problem of jet noise. For the first thrust, we show that when the basic state is appropriately constrained, the technique reverts to Linear, Parabolized and Global stability methods. The method is then verified by reproducing the growth of unstable modes in an inviscid Mach 6 entropy layer. The application to jet noise considers subsonic Mach 0.9 and perfectly expanded supersonic Mach 1.3 round jets. The results are compared with those from Parabolized Stability Equations (PSE) and LES solutions, respectively, considering monochromatic and multi-frequency perturbations. The NS-MFP method successfully reproduces key features of the modal response, including Strouhal number dependent directivity of noise radiation. Aspects related to the manner in which the mean basic state is obtained, whether from LES or Reynolds-averaged Navier-Stokes (RANS) equation are also explored. In particular, the sensitivity of the perturbation to whether the eddy viscosity is included or not, is examined in reference to maximum intensity of pressure fluctuation, directivity of noise radiation and the rate of fall-off of the spectra at higher Strouhal numbers. The results indicate that a closer match on the noise-radiation characteristics is obtained when effects of eddy-viscosity on the disturbances are neglected. (C) 2018 Elsevier Masson SAS. All rights reserved.

Interaction of shock waves with turbulent boundary layers can enhance the surface heat flux dramatically. Reynolds-averaged Navier-Stokes simulations based on a constant turbulent Prandtl number often give grossly erroneous heat transfer predictions in shock/boundary-layer interaction flows. This is due to the fact that the underlying Morkovin's hypothesis breaks down in the presence of shock waves; thus, the turbulent Prandtl number cannot be assumed to be a constant. In this paper, a new variable turbulent Prandtl number model based on linearized Rankine-Hugoniot conditions applied to shock-turbulence interaction is developed. The turbulent Prandtl number is a function of the shock strength, and a shock function is proposed to identify the location and strength of shock waves. The shock function also simulates the postshock relaxation of the turbulent heat flux, which is akin to that observed in canonical shock-turbulence interaction. The model is combined with the well-validated shock-unsteadiness k- model and is applied to the complex shock topology observed in oblique shock/turbulent boundary-layer interactions. Comparison with experimental data shows significant improvement in the surface heat transfer rate in the interaction region, both for attached and separated shock/boundary-layer interaction cases. The shock function is also used to propose a robust form of the existing shock-unsteadiness k- model that simplifies the numerical implementation enormously.

Recently Ram, Geva, and Sadot [J. Fluid Mech. 768, 219-235 (2015)] showed, experimentally, the formation of a secondary Mach stem generated from the reflection of the primary Mach stem in the aerodynamic regime. Such a phenomenon has never been observed, either experimentally or numerically, in the framework of weak acoustic shocks. In this work, the formation of a secondary Mach stem is observed from the reflection of acoustic shock waves on a convex-concave boundary giving rise to a complex five-shock pattern. This study is fully numerical and is based on the numerical solution of a nonlinear acoustic system of equations using a recently developed discontinuous Galerkin solver. (C) 2018 Acoustical Society of America

Asymptotic solutions are obtained for the 2D Euler system for non-ideal gases with appropriate boundary conditions which describe the diffraction of a weak shock at a wedge; the non-ideal gas effects are characterized by a van der Waals type equation of state. The behavior of the flow configuration influenced by the non-ideal gas effects, that includes the local structure near a singular point, is studied in detail.

High-speed turbulent flows with shock waves are characterized by high localized surface heat transfer rates. Computational predictions are often inaccurate due to the limitations in modelling of the unclosed turbulent energy flux in the highly non-equilibrium regions of shock interaction. In this paper, we investigate the turbulent energy flux generated when homogeneous isotropic turbulence passes through a nominally normal shock wave. We use linear interaction analysis where the incoming turbulence is idealized as being composed of a collection of two-dimensional planar vorticity waves, and the shock wave is taken to be a discontinuity. The nature of the postshock turbulent energy flux is predicted to be strongly dependent on the angle of incidence of the incoming waves. The energy flux correlation is also decomposed into its vortical, entropy and acoustic contributions to understand its rapid non-monotonic variation behind the shock. Three-dimensional statistics, calculated by integrating two-dimensional results over a prescribed upstream energy spectrum, are compared with available data from direct numerical simulations. A detailed budget of the governing equation is also considered in order to gain insight into the underlying physics.

The increasing global warming is most likely to affect the magnitude and pattern of wind at a regional level and such an effect may or not follow the trend predicted at the global scale. Regional level exercises are therefore necessary while making decisions related to engineering infrastructure. In this paper an attempt is made to know the extent of change in design as well as operational wind conditions at two offshore locations along the west coast of India. The design wind speeds with return periods of 10, 50 and 100 years derived for two 30-year time slices in the past and future are compared. In two separate exercises the past and future wind at the local level is simulated by empirical downscaling as well as by interpolation of the general circulation model (GCM) output. Both sets of past and future data are fitted to the Generalized Pareto as well as Weibull distributions using the peak over threshold method to extract long term wind speeds with a specified return. It is noticed that at the given locations the operational and design wind may undergo an increase of around 11%-14% when no downscaling is adopted and 14%-17% when the GCM data are downscaled. Although these figures may suffer from a certain level of statistical uncertainty the study points out to take a relook into the safety margins kept in the design and operation of ocean structures in the light of global warming. (C) 2014 Elsevier Ltd. All rights reserved.

Reynolds-averaged turbulence models can result in large numerical error at flow discontinuities like shock waves. This is due to the nonconservative nature of the source terms in the governing equations. In this paper, the k-epsilon turbulence model is used to compute the canonical interaction of a normal shock with homogeneous isotropic turbulence. The characteristics of the nonconservative error is studied as a function of shock strength, grid resolution, and upstream turbulence level. The model equations are cast in an equivalent conservation form that gives physically consistent results at a shock wave. The predicted amplifications of turbulent kinetic energy and its dissipation rate match direct numerical simulation data and linear theory estimates over a range of Mach numbers.

Interaction of turbulent fluctuations with a shock wave plays an important role in many high-speed flow applications. This paper studies the amplification of enstrophy, defined as mean-square fluctuating vorticity, in homogeneous isotropic turbulence passing through a normal shock. Linearized Navier–Stokes equations written in a frame of reference attached to the unsteady shock wave are used to derive transport equations for the vorticity components. These are combined to obtain an equation that describes the evolution of enstrophy across a time-averaged shock wave. A budget of the enstrophy equation computed using results from linear interaction analysis and data from direct numerical simulations identifies the dominant physical mechanisms in the flow. Production due to mean flow compression and baroclinic torques are found to be the major contributors to the enstrophy amplification. Closure approximations are proposed for the unclosed correlations in the production and baroclinic source terms. The resulting model equation is integrated to obtain the enstrophy jump across a shock for a range of upstream Mach numbers. The model predictions are compared with linear theory results for varying levels of vortical and entropic fluctuations in the upstream flow. The enstrophy model is then cast in the form of$k$–$\epsilon $equations and used to compute the interaction of homogeneous isotropic turbulence with normal shocks. The results are compared with available data from direct numerical simulations. The equations are further used to propose a model for the amplification of turbulent viscosity across a shock, which is then applied to a canonical shock–boundary layer interaction. It is shown that the current model is a significant improvement over existing models, both for homogeneous isotropic turbulence and in the case of complex high-speed flows with shock waves.

The effectiveness of measures in protecting the coast against natural hazards depends on the extent of run-up by ocean waves, which is an essential parameter in their planning and design. Although, several formulae have been derived in the past for estimation of run-up in laboratory studies for a variety of wave front structures, certain uncertainties still remain pertaining to flat slopes and long waves. To understand the performance characteristics of vegetation in attenuating run-up, a comprehensive experimental investigation was taken up. The studies were carried out with regular and cnoidal waves propagating over a plane slope of 1:30 in the presence and absence of vegetation of different characteristics. The results on the variation of dimensionless run-up as a function of wave and vegetal parameters are presented and discussed in this paper. � 2012, the Coastal Education & Research Foundation (CERF). � 2012 Coastal Education & Research Foundation.

In hypersonic flows, the interaction of a shock wave with a turbulent boundary layer can result in flow separation and high aerothermal loads. In this paper, cone flare configurations with different flare angles and freestream Mach numbers are simulated using Reynolds-averaged Navier Stokes method, and results are compared with experimental data. The standard Spalart-Allmaras and k-omega turbulence models do not predict flow separation at the cone flare junction, and therefore yield a large deviation from the surface pressure measurements. Sinha et al. ("Modeling Shock-Unsteadiness in Shock/Turbulence Interaction," Physics of Fluids, Vol. 15, No. 8, 2003, pp. 2290-2297) proposed a shock-unsteadiness model to account for the effect of unsteady shock motion in a steady mean flow. The shock-unsteadiness correction damps turbulence amplification at the shock and results in significant improvement in predicting flow separation and reattachment. The flow topology in the interaction region, in terms of the pattern of shocks and expansion waves, is predicted correctly by the modified turbulence models. The resulting surface pressure distribution matches experimental data well.

Prominent subsurface reflections from two GPR transect marked four lithological anomalies below Avis Island coral reefs. These scarps dip 5-10� towards sea and they consist of sands with more than 30-40% heavy mineral concentrations that produce distinct subsurface reflections that make possible to locate the buried erosional scarps. Heavy minerals are considered as the indicators of erosion as well as a proxy for sediment transport of extreme wave events. Heavy minerals including magnetite have higher magnetic susceptibility values: L1a:�644.6; �L1b:�556.8, L2a: 584.2 and L2b: 612�10-5�SI units to the background magnetic susceptibility of 5-10�10-5�SI units for quartz-rich sands suggest severe reworking process during an extreme wave event. The two profiles (L1 and L2) with four paleoscarps: L1a at a distance of 10 m from the shore, L2a approximately 15 m from the shore, L2b around 30 m from the shore and L1b nearly 35 m from the shore and the corresponding age of the dated coral above the paleoscarps increases towards land exhibiting progradation sequence. These subsurface reflections of paleoscarps were found at a depth of 1-1.5 m below the ground surface beneath the reported age of coral reefs suggesting that these coral reefs and the paleoscarps are found due to the same event.

'Der Beitrag untersucht den Prozess ausländischer Unterstützung für die Zivilgesellschaften in den postsowjetischen Staaten und die damit verbundenen Implikationen unter besonderer Berücksichtigung der 'farbigen Revolutionen'. In Serbien (2000), Georgien (2003), der Ukraine (2004) und Kirgisistan (2005) wird allgemein die Rolle der Nichtregierungs- und der Jugendorganisationen beim Organisieren gesellschaftlichen Protests als das eigentliche, kritische Element während der 'farbigen Revolutionen' angesehen. Im Gegensatz zu verbreiteten Auffassungen wird die These vertreten, dass diese 'Revolutionen' keine direkte Konsequenz der gewachsenen externen Unterstützung für die Zivilgesellschaften waren. Stattdessen wird den gesellschaftlichen Bewegungen eine Schlüsselrolle innerhalb der 'farbigen Revolutionen' zugeschrieben. Diese verwarfen das westliche Modell rigider, hierarchisch strukturierter Organisation zugunsten deutlich flexibler strukturierter 'rhizomischer', transnationaler Formen.' (Autorenreferat)

The Lie group of point transformations, which leave the equations for plane and radially symmetric flows of a non-ideal gas invariant, are used to obtain an exact solution that exhibits space-time dependence. We consider the propagation of a weak discontinuity through a state, characterized by this solution. Further, the evolution of a characteristic shock and its interaction with the weak discontinuity are studied. The properties of reflected and transmitted waves and the jump in shock acceleration, influenced by the incident wave amplitude and the van der Waals excluded volume, are completely characterized, and certain observations are noted in respect of their contrasting behaviour. (c) 2006 Elsevier B. V. .

Ricardo WAVE was used to simulate the hydrogen internal combustion engine used in Texas Tech University’s FutureTruck Ford Explorer. Initially, a naturally aspirated gasoline engine was simulated, followed by the supercharged hydrogen engine. The objective of these simulations was to maximize power of the hydrogen engine, while minimizing the emissions and fuel consumption. Among the variables which were changed, were the equivalence ratio, compression ratio, throttle opening, camshaft timing, and exhaust size. The simulation results studied included the volumetric efficiency, fuel consumption, as well as NO emissions. Several results were compared to the gasoline baseline model.

We examine the uniformly imploding pellets or shells, which are driven to implode by the action of compressional forces. Besides providing the precise time of implosion we discuss continuation of the solution beyond the time of implosion using WTC expansions. Our quantitative analysis confirms the observations of D. L. Book and I. B. Bernstein (1980).

Air-water upward annular flow experiments were conducted in a 10.8 m long tube of 31.8 mm internal diameter. Local values of the pressure gradient, film thickness, wall shear stress, film flow rate, disturbance wave velocity and frequency were measured over a range of gas and liquid flow rates. The results show that rapid changes in the film flow parameters occur within the first 50 tube diameters or so from the inlet. Entrained fraction and the film thickness appear to be the slowest to respond and these may take 100 to 300 tube diameters to develop fully. ? 2001 Elsevier Science Ltd. All rights reserved.

The dynamic pressure distribution around a cylinder tilted along and against the principal wave direction is measured. The cylinder was exposed to the action of random waves in the presence and absence of extreme waves. Six inclinations from the vertical plane, three along and three against the wave direction, were considered. The cylinder in upright position was also studied. The variation of dimensionless peak pressure (pressure maximum/average highest one-third wave height, H(1/3)) with the relative wave height (maximum wave height/H(1/3)) for locations facing the wave and at the rear of the cylinder for different angles of inclinations of the cylinder are reported for the two kinds of waves mentioned earlier. The statistical properties of the different asymmetries in the pressure traces are also discussed.The dynamic pressure distribution around a cylinder tilted along and against the principal wave direction is measured. The cylinder was exposed to the action of random waves in the presence and absence of extreme waves. Six inclinations from the vertical plane, three along and three against the wave direction, were considered. The cylinder in upright position was also studied. The variation of dimensionless peak pressure (pressure maximum/average highest one-third wave height, H1/3) with the relative wave height (maximum wave height/H1/3) for locations facing the wave and at the rear of the cylinder for different angles of inclinations of the cylinder are reported for the two kinds of waves mentioned earlier. The statistical properties of the different asymmetries in the pressure traces are also discussed.

The compactly supported orthogonal wavelet bases developed by Daubechies are used in the Galerkin scheme for a class of one-dimensional first-order quasilinear conservation equations with perturbed dissipative terms. We first develop a recursive algorithm to obtain the wavelet coefficients of a dissipative term of the type un or un/1 from those of u and then develop the wavelet-Galerkin solutions to several differential equations containing such dissipative terms. It is seen that the wavelet bases are capable of producing stable solutions throughout the domain except in the vicinity of the shock formation, where oscillations are seen to occur. Unlike the Fourier bases, which are known to produce oscillations which are smaller in magnitude but present throughout the domain, the oscillations produced by the wavelet bases are confined to the vicinity of the shocks. Further, we show that these oscillations may be smoothed out by a three-term averaging method. Copyright ? 1999 John Wiley & Sons, Ltd.

The dynamic pressures due to random waves of predefined spectral characteristics exerted on a semicircular breakwater model at five different elevations along the depth are measured. In addition, the wave run-up on the model and its reflection characteristics are measured. The results on the variation of the frequency pressure spectra along the depth and the run-up spectra are reported in this paper. The average spectral characteristics as well as statistical properties of the above two parameters are presented. The average reflection coefficient is reported as a function of the wave steepness, described as the ratio of the significant wave height to the square of the peak period. ? 1997 Elsevier Science Ltd.

A sea water intake well of size 20 m diameter and 15.5 m height in a water depth of 9.8 m is proposed north of the Visakhapatnam Port for a project to extract magnesia from sea water. A 1:25 scale model of the intake well was tested in the wave basin of the Ocean Engineering Centre, Indian Institue of Technology, Madras to measure the wave forces and moments on the intake well and the variation of water levels inside and outside the well. Accordingly, an intake well model of 0.8 m diameter and 0.62 m height was fabricated and fixed over a false bottom in a wave basin. The well model was subjected to the action of both regular waves for two test conditions, intake well inlet closed during installation and intake well inlet open. The experimental results on wave forces and moments were compared with the results of the Linear Diffraction Theory. The water level inside the well was measured to determine the submergence of suction pipes of pumps and location of the inlet opening of the intake well. The wave crest elevation in front of the well was also measured in order to fix the deck level of the well so as to avoid water overspill onto the deck. The salient results of the present study are presented and discussed in this paper.A sea water intake well of size 20 m diameter and 15.5 m height in a water depth of 9.8 m is proposed north of the Visakhapatnam Port for a project to extract magnesia from sea water. A 1:25 scale model of the intake well was tested in the wave basin of the Ocean Engineering Centre, Indian Institute of Technology, Madras to measure the wave forces and moments on the intake well and the variation of water levels inside and outside the well. Accordingly, an intake well model of 0.8 m diameter and 0.62 m height was fabricated and fixed over a false bottom in a wave basin. The well model was subjected to the action of both regular waves for two test conditions, intake well inlet closed during installation and intake well inlet open. The experimental results on wave forces and moments were compared with the results of the Linear Diffraction Theory. The water level inside the well was measured to determine the submergence of suction pipes of pumps and location of the inlet opening of the intake well. The wave crest elevation in front of the well was also measured in order to fix the deck level of the well so as to avoid water overspill onto the deck. The salient results of the present study are presented and discussed in this paper.