Damage of a high-energy solid propellant and its effects on combustion

In order to improve the safety of high-energy solid propellants, a study is carried out for the effects of damage on the combustion of the NEPE (Nitrate Ester Plasticized Polyether) propellant. The study includes: (1) to introduce damage into the propellants by means of a large-scale drop-weight apparatus; (2) to observe microstructural variations of the propellant with a scanning electron microscope (SEM) and then to characterize the damage with density measurements; (3) to investigate thermal decomposition; (4) to carry out closed-bomb tests. The NEPE propellant can be considered as a viscoelastic material. The matrices of damaged samples are severely degraded, but the particles are not. The results of the thermal decomposition and closed-bomb tests show that the microstructural damage in the propellant affects its decomposition and burn rate.     

Measurement of the flow field in a diesel engine combustion chamber after combustion by cross-correlation of high-speed photographs

A cellular cross-correlation technique is applied to high-speed photographs of the luminous phase of combustion in a high-speed direct-injection diesel engine. The method enables the velocity and vorticity distributions in the combustion chamber to be evaluated. The results obtained from the basic technique are refined to remove spurious results and to complete the definition of the flow field by applying data validation, interpolation, and smoothing. The velocity and vorticity fields evaluated at two swirl ratios show the way in which the basically solid body swirl motion interacts with the fuel jets in the combustion chamber. A better understanding of the post-combustion fluid motion is obtained, and this should be of help in validating CFD codes and also the design of engines.The combustion photographs which provided the data for this work were obtained by Mr. E. H. Clough, K. K. Rao, P. Gomes and R. Pruce. Funding for the programme was provided by the UK Science and Engineering Research Council. Financial support for one of the authors (J.-H. S.) was provided by the Sino-British Friendship Scholarship Scheme. To all these people and organisations the authors express their grateful thanks.     

Two modes of operation of a model combustion chamber as a thermoacoustic autooscillating system

It is shown that soft and hard modes of operation of a model combustion chamber as an autooscillating system are possible. In the case of oscillations with transverse acoustic waves we: a) determined the ranges of these modes experimentally; b) detected oscillatory hysteresis (persistence) effects and observed the abrupt appearance and disappearance of oscillations during gradual variation of the parameters. We also noted excitation of autooscillations when finite perturbations acted on the gas column in the combustion chamber in the case of the hard mode.     

Numerical model of the aspiration system of an internal combustion engine

A physicomathematical model of flow in the aspiration system of an internal combustion engine operating in a “cold” regime, i.e., for a prescribed motion of the crankshaft, has been constructed. An ideal single-species gas is used. Results of a series of calculations for a time interval of five operation cycles are presented. Deceased. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 6, pp. 125–131, November–December, 1998.     

Numerical modeling of turbulent-transfer processes in a mixing zone

The series of moments of the velocity field in a two-dimensional zone of mixing is calculated in this article by numerically solving a system of turbulent-transfer differential equations derived from an equation for a single-point distribution function of the velocity pulsation field [1] and simplified to an approximation of the boundary layer. The closed form of the transfer equation is obtained at the level of the third moments using the Millionshchikov hypothesis [2]. The differential operator of the system under this closure turns out to be weakly hyperbolic [3], and not parabolic. A difference scheme is proposed that realizes the method of matrix fitting [4]. A comparison is carried out with an experiment [5, 6].     

Numerical modeling of the turbulent convection mode in a vertical layer

An approach to the numerical modeling of turbulent natural convection modes on the basis of two-dimensional nonstationary Navier-Stokes equations without the use of additional empirical information is elucidated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkostii Gaza, No. 5, pp. 8–15, September–October, 1977.The authors are grateful to A. G. Kirdyashkin for consultations on the method and results of the experiments to G. S. Glushko for useful remarks, and to K. G. Dubovik for aid in performing the computations.     

Numerical studies of nonlinear wave processes in a liquid and a deformable solid during high-speed impact interaction

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 134–143, March–April, 1991.     

Numerical modeling of the stabilization of a supersonic flat-plate boundary layer by a porous coating

On the basis of a numerical solution of the two-dimensional Navier-Stokes equations, the stability and the receptivity of a supersonic (M_∞ = 6) boundary layer on a flat plate with a passive porous coating partially absorbing flow disturbances is studied. The results of direct numerical simulation are in good agreement with the data of the linear stability theory. The studies confirm the possibility of effectively stabilizing the second mode of the supersonic boundary layer using porous coatings.     

Numerical modeling of detonation combustion of hydrogen-air mixtures in a convergent-divergent nozzle

The flow of igniting hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered. A possibility of stabilizing detonation combustion is numerically investigated at different freestream Mach numbers with account for nonuniform distribution of hydrogen concentration at the nozzle entry. The investigation is performed on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical reactions is used. The calculated thrust is compared with the drag of a conical housing containing the supersonic nozzle considered.     

Holographic particle image velocimetry applied to the flow within the cylinder of a four-valve internal combustion engine

A holographic particle-image velocimetry (HPIV) system is developed to investigate the in-cylinder air flow in a motored four-valve engine operated at 1,500 rpm. Image aberrations introduced by the optical liner of the engine are optically eliminated. The use of a reference hologram to compensate for errors induced by fine reference beam misalignments is described. The remaining errors are quantitatively discussed in the text. The application of a wavelength selected laser diode for hologram reconstruction is discussed. High-resolution velocity measurements of the in-cylinder flow are made in axial planes during the intake and compression stroke. Prospects and limitations to full three-dimensional extensions of the HPIV system are discussed. The results show with emphasis on large- and small-scale flow structures the HPIV system to be a reliable diagnostic tool for internal combustion engines.     

Numerical modeling of the formation of aerosol particles in jet engine plumes

The formation of liquid sulfate aerosols in the isobaric axisymmetric plume of a subsonic aircraft is modeled numerically. The specific features of the appearance and evolution of sulfate aerosols attributable to 2D effects, such as the parameter nonuniformity in the initial section (at the nozzle outlet), mixing of the hot engine jet with the cold air stream, and the transverse turbulent diffusion of aerosol particles and gas mixture components. The equations of gas dynamics for a turbulent axisymmetric jet, the equations of chemical kinetics, the equations for the liquid fractions (water and sulfuric acid), and the relations for the binary nucleation, condensation growth and coagulation of aerosol particles are used. The distributions of the parameters determining the formation of the aerosol phase in the exhaust plume of a B-747 aircraft are obtained and the geometry of the nucleation zone in this plume is determined.     

Numerical investigations of cooling holes system role in the protection of the walls of a gas turbine combustion chamber

Numerical simulations in a gas turbine Swirl stabilized combustor were conducted to investigate the effectiveness of a cooling system in the protection of combustor walls. The studied combustion chamber has a high degree of geometrical complexity related to the injection system as well as the cooling system based on a big distribution of small holes (about 3,390 holes) bored on the flame tube walls. Two cases were considered respectively the flame tube without and with its cooling system. The calculations were carried out using the industrial CFD code FLUENT 6.2. The various simulations made it possible to highlight the role of cooling holes in the protection of the flame tube walls against the high temperatures of the combustion products. In fact, the comparison between the results of the two studied cases demonstrated that the walls temperature can be reduced by about 800°C by the mean of cooling holes technique.     

LDV measurements of the flow inside the combustion chamber of a 4-valve D.I. diesel engine with axisymmetric piston-bowls

 LDV measurements of the tangential and radial velocity components have been performed to investigate the flow patterns inside a 4-valve single cylinder diesel engine for various engine speeds, swirl numbers and piston-bowl geometries, under conditions similar to those of a production engine. The work focused on the near-wall region of the axisymmetric combustion chambers where the strong swirl-squish and spray-wall interactions take place. The different axial flow stratification observed in both velocity components has confirmed the influence of piston shape and intake configuration on the flow patterns and turbulence levels near compression TDC. Measured values are in reasonable agreement with those provided by a two-zone phenomenological model. Received: 6 November 1995 / Accepted: 12 April 1996     

Numerical modeling of the rotation of a solid body with a liquid-filled cavity having radial ribs

The boundary-value problem of unsteady vortex flow of a viscous incompressible fluid in a cylindrical vessel with radial ribs rotating at a variable angular velocity is solved using a finite-difference method. The results of the solution are used to calculate the motion of a system of a solid body and a cavity filled with a liquid. The results are compared with available experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 135–139, March–April, 2007.     

Particle-image velocimetry measurement in the exhaust of a solid rocket motor

Successful particle-image velocimetry (PIV) measurements have been demonstrated in the exhaust plume of a small solid rocket motor. Background irradiance, high velocities reaching 630 m/s, temperatures exceeding 3000 K and lack of control over the seeding inside the plume make this flow field one of the more challenging environments for the application of the PIV technique. It is shown that the particulates ejected along with the exhaust gases are well suited as PIV marker particles, although nonuniform spatial distribution causes substantial loss of vectors. In the region investigated, the axial mean velocity profiles exhibit self-similarity despite the compressible, nonisothermal, multiphase nature of the flow.     

Numerical studies of shock focusing induced by reflection of detonation waves within a hemispherical implosion chamber

The initiation and the propagation of detonation waves in a hemispherical chamber and the imploding shock waves that are the reflected detonation waves at the chamber wall are numerically investigated. The effects of the boundary layer and the non-uniformity of the flow field induced by the detonation wave on the imploding shock stability are examined. It is found that the effect of the boundary layer separation on the chamber wall has the strongest effect on the implosion focus.