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James C Mcwilliams - One of the best experts on this subject based on the ideXlab platform.
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baroclinic instability of axially symmetric Flow over sloping bathymetry
Journal of Fluid Mechanics, 2016Co-Authors: Aviv Solodoch, Andrew L Stewart, James C McwilliamsAbstract:Under consideration for publication in J. Fluid Mech. Baroclinic instability of axially-symmetric Flow over sloping bathymetry Aviv Solodoch 1 †, Andrew L. Stewart 1 and James C. McWilliams 1 Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA (Received xx; revised xx; accepted xx) Observations and models of deep ocean boundary currents show that they exhibit complex variability, instabilities and eddy shedding, particularly over continental slopes that curve horizontally, for example around coastal peninsulas. In this article the authors investigate the source of this variability by characterizing the properties of baroclinic instability in mean Flows over horizontally curved bottom slopes. The classical 2-layer quasi-geostrophic solution for linear baroclinic instability over sloping bottom topography is extended to the case of azimuthal mean Flow in an annular channel. To facilitate comparison with the classical straight channel instability problem of uniform mean Flow, the authors focus on comparatively simple Flows in an annulus, namely uniform azimuthal velocity and solid-body rotation. Baroclinic instability in solid-body rotation Flow is analytically analogous to the instability in uniform straight channel Flow due to several identical properties of the mean Flow, including vanishing strain rate and vorticity gradient. The instability of uniform azimuthal Flow is numerically similar to straight channel Flow instability as long as the mean Barotropic azimuthal velocity is zero. Nonzero Barotropic Flow generally suppresses the instability via horizontal curvature- induced strain and Reynolds stresses work. An exception occurs when the ratio of the bathymetric to isopycnal slopes is close to (positive) one, as is often observed in the ocean, in which case the instability is enhanced. A non-vanishing mean Barotropic Flow component also results in a larger number of growing eigenmodes and in increased non-normal growth. The implications of these findings for variability in deep western boundary currents are discussed. 1. Introduction Baroclinic instability is one of the main energy conversion processes to and from the mesoscale in the ocean (McWilliams 2008). The baroclinic source of energy, available potential energy due to tilting of isopycnals (constant density surfaces), is ubiquitous. Studies based on high-resolution altimetry (Chelton et al. 2011) reveal that virtually all areas of the world’s oceans are sources of mesoscale eddies, and therefore may be baroclinically unstable. A few of the many roles mesoscale eddies play in the ocean are: supporting the forward and inverse turbulent energy cascades, relaxing isopycnal slopes and thus restratifying the ocean, vertical transfer of momentum via the eddy form stress and transport, and ventilation and subdaction of tracers (McWilliams 2008; Dong et al. Baroclinic eddy variability peaks in the ocean near strong persistent currents (Chelton et al. 2011), such as large boundary currents (e.g., the Gulf Stream). The task of measuring and characterizing eddy generation mechanisms is more challenging for deep † Email address for correspondence: asolodoch@atmos.ucla.edu
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baroclinic instability of axially symmetric Flow over sloping bathymetry
Journal of Fluid Mechanics, 2016Co-Authors: Aviv Solodoch, Andrew L Stewart, James C McwilliamsAbstract:Observations and models of deep ocean boundary currents show that they exhibit complex variability, instabilities and eddy shedding, particularly over continental slopes that curve horizontally, for example around coastal peninsulas. In this article the authors investigate the source of this variability by characterizing the properties of baroclinic instability in mean Flows over horizontally curved bottom slopes. The classical two-layer quasi-geostrophic solution for linear baroclinic instability over sloping bottom topography is extended to the case of azimuthal mean Flow in an annular channel. To facilitate comparison with the classical straight channel instability problem of uniform mean Flow, the authors focus on comparatively simple Flows in an annulus, namely uniform azimuthal velocity and solid-body rotation. Baroclinic instability in solid-body rotation Flow is analytically analogous to the instability in uniform straight channel Flow due to several identical properties of the mean Flow, including vanishing strain rate and vorticity gradient. The instability of uniform azimuthal Flow is numerically similar to straight channel Flow instability as long as the mean Barotropic azimuthal velocity is zero. Non-zero Barotropic Flow generally suppresses the instability via horizontal curvature-induced strain and Reynolds stress work. An exception occurs when the ratio of the bathymetric to isopycnal slopes is close to (positive) one, as is often observed in the ocean, in which case the instability is enhanced. A non-vanishing mean Barotropic Flow component also results in a larger number of growing eigenmodes and in increased non-normal growth. The implications of these findings for variability in deep western boundary currents are discussed.
Ezio Spessa - One of the best experts on this subject based on the ideXlab platform.
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temperature variations in the simulation of high pressure injection system transient Flows under cavitation
International Journal of Heat and Mass Transfer, 2008Co-Authors: Andrea Catania, Alessandro Ferrari, Ezio SpessaAbstract:Abstract Temperature variations and their effects on the simulation of unsteady pipe Flows, in the presence of pressure-wave induced cavitation, were investigated with reference to high-pressure fuel injection systems. The thermal effects due to the compressibility of the liquid and to the thermodynamic process in the cavitating Flow mixture were analyzed. To that end, the energy conservation equation was applied, in addition to the mass-continuity and momentum-balance equations, along with the constitutive state equation of the fluid. In particular, for the liquid, the physical properties (i.e., bulk modulus of elasticity, density, isothermal speed of sound, thermal expansivity, kinematic viscosity, specific heat at constant pressure) were implemented as functions of pressure and temperature in a closed analytical form matching carefully determined experimental data. Consistent with virtually negligible combined effects of heat transfer and viscous power losses involved in the Flow process, the equation of energy was reduced to a state relation among the fluid thermodynamic properties, leading to a Barotropic Flow model. A comparison between isentropic and isothermal evolutions in the pure liquid regions was carried out for evaluating the influence of the temperature variation simulation on the macroscopic results given by local pressure time-histories. Besides, for cavitation analysis, different thermodynamic transformations of the vapor–liquid mixture were considered and compared. A recently developed conservative numerical model of general application, based on a Barotropic Flow model, was applied and further assessed through the comparison of prediction and measurement results on injection-system performance. A conventional pump-line-nozzle system was considered for this purpose, being relevant to model evaluation for its pressure-wave dynamics and also because it was subject to severely cavitating Flow conditions at part loads. Predicted time-histories of injector-needle lift and pressure at two pipe locations were compared to experimental results. This substantiated the validity and robustness of the conservative model taking temperature variation effects into account, in the simulation of high-pressure injection-system transient Flows with great degree of accuracy, even in the presence of cavitation induced discontinuities. The thermal effects due to the temperature variations in the liquid fuel and in the cavitating mixture were analyzed and discussed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous two phase Barotropic Flow model
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2006Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase Barotropic Flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal Flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe Flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating Flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the Flow discontinuities induced by them were numerically predicted and analyzed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous Barotropic Flow model
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2003Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase Barotropic Flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal Flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe Flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating Flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the Flow discontinuities induced by them were numerically predicted and analyzed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous Barotropic Flow model
ASME 2003 Internal Combustion Engine and Rail Transportation Divisions Fall Technical Conference ICERT2003, 2003Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for simulation of transmission-line unsteady fluid-dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e. cavitation induced by wave propagation, was proposed on the basis of a homogeneous Barotropic mixture model of a pure liquid in equilibrium with its vapor and a gas, both dissolved and undissolved. For the pure liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic state equation which was derived from energy considerations. Nevertheless, in the cavitation regions, an isothermal Flow was retained which is consistent with negligible thermal effects due to vaporization because of the tiny amounts of liquid involved. A novel implicit, conservative, one step, symmetrical and trapezoidal scheme of the second-order accuracy was applied to solve the hyperbolic partial differential equations governing the pipe Flows. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was of relevance to the model assessment because it presented severely cavitating Flow conditions. The predicted pressure time histories at two pipe locations and injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating cavitation inception and desinence with great degree of accuracy. Cavitation transients and the Flow discontinuities induced by them were numerically analyzed and discussed.© 2003 ASME
Peter D Killworth - One of the best experts on this subject based on the ideXlab platform.
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long extratropical planetary wave propagation in the presence of slowly varying mean Flow and bottom topography part ii ray propagation and comparison with observations
Journal of Physical Oceanography, 2003Co-Authors: Peter D Killworth, Jeffrey R BlundellAbstract:Ray theory is used to predict phase and group velocities for long planetary waves under realistic, albeit slowly varying, oceanic conditions. The results are compared with local theory using fields smoothed to the same amount (9° latitude/longitude) as well as those with much less smoothing (1°). The agreement is excellent, showing that local theory forms a good proxy for ray theory results. The predicted speeds agree well with observations of planetary waves deduced from sea surface height data. The theory uses purely baroclinic mean Flow; the inclusion of Barotropic Flow has little effect except at high latitudes.
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the speed of observed and theoretical long extratropical planetary waves
Journal of Physical Oceanography, 1997Co-Authors: Peter D Killworth, Dudley B. Chelton, Roland A. De SzoekeAbstract:Planetary or Rossby waves are the predominant way in which the ocean adjusts on long (year to decade) timescales. The motion of long planetary waves is westward, at speeds $ 1c m s 2 1. Until recently, very few experimental investigations of such waves were possible because of scarce data. The advent of satellite altimetry has changed the situation considerably. Curiously, the speeds of planetary waves observed by TOPEX/Poseidon are mainly faster than those given by standard linear theory. This paper examines why this should be. It is argued that the major changes to the unperturbed wave speed will be caused by the presence of baroclinic east‐ west mean Flows, which modify the potential vorticity gradient. Long linear perturbations to such Flow satisfy a simple eigenvalue problem (related directly to standard quasigeostrophic theory). Solutions are mostly real, though a few are complex. In simple situations approximate solutions can be obtained analytically. Using archive data, the global problem is treated. Phase speeds similar to those observed are found in most areas, although in the Southern Hemisphere an underestimate of speed by the theory remains. Thus, the presence of baroclinic mean Flow is sufficient to account for the majority of the observed speeds. It is shown that phase speed changes are produced mainly by (vertical) mode-2 east‐west velocities, with mode-1 having little or no effect. Inclusion of the mean Barotropic Flow from a global eddy-admitting model makes only a small modification to the fit with observations; whether the fit is improved is equivocal.
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the development of a free surface bryan cox semtner ocean model
Journal of Physical Oceanography, 1991Co-Authors: Peter D Killworth, David A Stainforth, D J Webb, Stephen M PatersonAbstract:Abstract A version of the Bryan–Cox–Semtner numerical ocean general circulation model, adapted to include a free surface, is described. The model is designed for the following uses: tidal studies (a tidal option is explicitly included); assimilation of altimetric data (since the surface elevation is now a prognostic variable); and in situations where accurate relaxation to obtain the streamfunction in the original model is too time consuming. Comparison is made between a 300-year run of the original model and the free-surface version, using a very coarse North Atlantic calculation as the basis. The results are very similar, differing only in the streamfunction over topography; this is to be expected, since the treatment of topographic torques on the Barotropic Flow differs because of the nature of the modifications.
Aviv Solodoch - One of the best experts on this subject based on the ideXlab platform.
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baroclinic instability of axially symmetric Flow over sloping bathymetry
Journal of Fluid Mechanics, 2016Co-Authors: Aviv Solodoch, Andrew L Stewart, James C McwilliamsAbstract:Under consideration for publication in J. Fluid Mech. Baroclinic instability of axially-symmetric Flow over sloping bathymetry Aviv Solodoch 1 †, Andrew L. Stewart 1 and James C. McWilliams 1 Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA (Received xx; revised xx; accepted xx) Observations and models of deep ocean boundary currents show that they exhibit complex variability, instabilities and eddy shedding, particularly over continental slopes that curve horizontally, for example around coastal peninsulas. In this article the authors investigate the source of this variability by characterizing the properties of baroclinic instability in mean Flows over horizontally curved bottom slopes. The classical 2-layer quasi-geostrophic solution for linear baroclinic instability over sloping bottom topography is extended to the case of azimuthal mean Flow in an annular channel. To facilitate comparison with the classical straight channel instability problem of uniform mean Flow, the authors focus on comparatively simple Flows in an annulus, namely uniform azimuthal velocity and solid-body rotation. Baroclinic instability in solid-body rotation Flow is analytically analogous to the instability in uniform straight channel Flow due to several identical properties of the mean Flow, including vanishing strain rate and vorticity gradient. The instability of uniform azimuthal Flow is numerically similar to straight channel Flow instability as long as the mean Barotropic azimuthal velocity is zero. Nonzero Barotropic Flow generally suppresses the instability via horizontal curvature- induced strain and Reynolds stresses work. An exception occurs when the ratio of the bathymetric to isopycnal slopes is close to (positive) one, as is often observed in the ocean, in which case the instability is enhanced. A non-vanishing mean Barotropic Flow component also results in a larger number of growing eigenmodes and in increased non-normal growth. The implications of these findings for variability in deep western boundary currents are discussed. 1. Introduction Baroclinic instability is one of the main energy conversion processes to and from the mesoscale in the ocean (McWilliams 2008). The baroclinic source of energy, available potential energy due to tilting of isopycnals (constant density surfaces), is ubiquitous. Studies based on high-resolution altimetry (Chelton et al. 2011) reveal that virtually all areas of the world’s oceans are sources of mesoscale eddies, and therefore may be baroclinically unstable. A few of the many roles mesoscale eddies play in the ocean are: supporting the forward and inverse turbulent energy cascades, relaxing isopycnal slopes and thus restratifying the ocean, vertical transfer of momentum via the eddy form stress and transport, and ventilation and subdaction of tracers (McWilliams 2008; Dong et al. Baroclinic eddy variability peaks in the ocean near strong persistent currents (Chelton et al. 2011), such as large boundary currents (e.g., the Gulf Stream). The task of measuring and characterizing eddy generation mechanisms is more challenging for deep † Email address for correspondence: asolodoch@atmos.ucla.edu
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baroclinic instability of axially symmetric Flow over sloping bathymetry
Journal of Fluid Mechanics, 2016Co-Authors: Aviv Solodoch, Andrew L Stewart, James C McwilliamsAbstract:Observations and models of deep ocean boundary currents show that they exhibit complex variability, instabilities and eddy shedding, particularly over continental slopes that curve horizontally, for example around coastal peninsulas. In this article the authors investigate the source of this variability by characterizing the properties of baroclinic instability in mean Flows over horizontally curved bottom slopes. The classical two-layer quasi-geostrophic solution for linear baroclinic instability over sloping bottom topography is extended to the case of azimuthal mean Flow in an annular channel. To facilitate comparison with the classical straight channel instability problem of uniform mean Flow, the authors focus on comparatively simple Flows in an annulus, namely uniform azimuthal velocity and solid-body rotation. Baroclinic instability in solid-body rotation Flow is analytically analogous to the instability in uniform straight channel Flow due to several identical properties of the mean Flow, including vanishing strain rate and vorticity gradient. The instability of uniform azimuthal Flow is numerically similar to straight channel Flow instability as long as the mean Barotropic azimuthal velocity is zero. Non-zero Barotropic Flow generally suppresses the instability via horizontal curvature-induced strain and Reynolds stress work. An exception occurs when the ratio of the bathymetric to isopycnal slopes is close to (positive) one, as is often observed in the ocean, in which case the instability is enhanced. A non-vanishing mean Barotropic Flow component also results in a larger number of growing eigenmodes and in increased non-normal growth. The implications of these findings for variability in deep western boundary currents are discussed.
Andrea Catania - One of the best experts on this subject based on the ideXlab platform.
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temperature variations in the simulation of high pressure injection system transient Flows under cavitation
International Journal of Heat and Mass Transfer, 2008Co-Authors: Andrea Catania, Alessandro Ferrari, Ezio SpessaAbstract:Abstract Temperature variations and their effects on the simulation of unsteady pipe Flows, in the presence of pressure-wave induced cavitation, were investigated with reference to high-pressure fuel injection systems. The thermal effects due to the compressibility of the liquid and to the thermodynamic process in the cavitating Flow mixture were analyzed. To that end, the energy conservation equation was applied, in addition to the mass-continuity and momentum-balance equations, along with the constitutive state equation of the fluid. In particular, for the liquid, the physical properties (i.e., bulk modulus of elasticity, density, isothermal speed of sound, thermal expansivity, kinematic viscosity, specific heat at constant pressure) were implemented as functions of pressure and temperature in a closed analytical form matching carefully determined experimental data. Consistent with virtually negligible combined effects of heat transfer and viscous power losses involved in the Flow process, the equation of energy was reduced to a state relation among the fluid thermodynamic properties, leading to a Barotropic Flow model. A comparison between isentropic and isothermal evolutions in the pure liquid regions was carried out for evaluating the influence of the temperature variation simulation on the macroscopic results given by local pressure time-histories. Besides, for cavitation analysis, different thermodynamic transformations of the vapor–liquid mixture were considered and compared. A recently developed conservative numerical model of general application, based on a Barotropic Flow model, was applied and further assessed through the comparison of prediction and measurement results on injection-system performance. A conventional pump-line-nozzle system was considered for this purpose, being relevant to model evaluation for its pressure-wave dynamics and also because it was subject to severely cavitating Flow conditions at part loads. Predicted time-histories of injector-needle lift and pressure at two pipe locations were compared to experimental results. This substantiated the validity and robustness of the conservative model taking temperature variation effects into account, in the simulation of high-pressure injection-system transient Flows with great degree of accuracy, even in the presence of cavitation induced discontinuities. The thermal effects due to the temperature variations in the liquid fuel and in the cavitating mixture were analyzed and discussed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous two phase Barotropic Flow model
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2006Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase Barotropic Flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal Flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe Flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating Flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the Flow discontinuities induced by them were numerically predicted and analyzed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous Barotropic Flow model
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2003Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase Barotropic Flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal Flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe Flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating Flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the Flow discontinuities induced by them were numerically predicted and analyzed.
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a comprehensive thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous Barotropic Flow model
ASME 2003 Internal Combustion Engine and Rail Transportation Divisions Fall Technical Conference ICERT2003, 2003Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio SpessaAbstract:A general conservative numerical model for simulation of transmission-line unsteady fluid-dynamics has been developed and applied to high-pressure injection systems. A comprehensive thermodynamic approach for modeling acoustic cavitation, i.e. cavitation induced by wave propagation, was proposed on the basis of a homogeneous Barotropic mixture model of a pure liquid in equilibrium with its vapor and a gas, both dissolved and undissolved. For the pure liquid Flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a thermodynamic state equation which was derived from energy considerations. Nevertheless, in the cavitation regions, an isothermal Flow was retained which is consistent with negligible thermal effects due to vaporization because of the tiny amounts of liquid involved. A novel implicit, conservative, one step, symmetrical and trapezoidal scheme of the second-order accuracy was applied to solve the hyperbolic partial differential equations governing the pipe Flows. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was of relevance to the model assessment because it presented severely cavitating Flow conditions. The predicted pressure time histories at two pipe locations and injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating cavitation inception and desinence with great degree of accuracy. Cavitation transients and the Flow discontinuities induced by them were numerically analyzed and discussed.© 2003 ASME