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Recoil Arresting and Recoilless Guns
Published in Donald E. Carlucci, Sidney S. Jacobson, Ballistics, 2018
Donald E. Carlucci, Sidney S. Jacobson
We may then consider a portion of the same propelling charge granulation to burn within the rocket chamber. The rocket nozzle may now be defined by its throat area and expansion ratio. Typical recoilless gun contractions achieve a throat area of about 30% less than the bore area. The expansion ratio is equal to the ratio of the nozzle exit area to that of its throat. Many recoilless guns have expansion ratios of nearly 2.
Secondary Flow Investigations in Turbine Cascades
Published in Chunill Hah, Turbomachinery Fluid Dynamics and Heat Transfer, 2017
Antonio Perdichizzi, Marco Savini, Vincenzo Dossena
The evolution of the secondary flow field in plane at x/b = 1.9, versus the Mach number, is described by the results of Figure 7. Four outlet isentropic Mach numbers, (M2is = 0.32,0.72,1.15 and 1.38) were selected as representative respectively of low subsonic, high subsonic, transonic, and supersonic flow conditions. Increasing the expansion ratio, the secondary flow effects are progressively confined in the endwall region, and a generally lower loss level is found. The low energy fluid region on the suction side of the wake moves away from midspan, together with the passage vortex itself and the shed vortex, hence the flow is two-dimensional for a larger extent of the blade span. This feature is the effect of the larger acceleration taking place throughout the cascade. In fact, when the expansion ratio is increased, both inlet and outlet velocities increase, but the latter increases more, because of flow compressibility; if one considers that the secondary velocities are related to the inlet vorticity, i.e., to the inlet freestream velocity, it emerges that a less intense swirling flow takes place in the blade passage, relatively to the streamwise velocity. As a result the flow particles involved in the passage vortex within the blade channel experience a smaller number of revolutions.
A review of computational studies on the effect of physical variables in direct injection diesel engines
Published in Australian Journal of Mechanical Engineering, 2023
Lean fuel operation and high compression ratio favour diesel engines to result in high thermal efficiencies. The high compression ratio produces the high temperatures required to achieve auto-ignition, and the resulting high expansion ratio makes the engine discharge less thermal energy in the exhaust. The extra oxygen in the cylinders is necessary to facilitate complete combustion and to compensate for non-homogeneity in the fuel distribution. However, high flame temperatures predominate because locally stoichiometric air–fuel ratios prevail in such heterogeneous combustion processes (Borman and Gagland 1998). Consequently, diesel engine combustion generates large amounts of nitrogen oxides because of the high flame temperature in the presence of abundant oxygen and nitrogen (Kreso et al. 1988). Diesel engines are lean burn systems when overall air–fuel ratios are considered, commonly with an air excess ratio λ = 1.5–1.8 on full loads and higher equivalence ratio (λ) values as load reduces. During idling, for instance, the air to fuel ratio of a modern diesel engine can be 10-fold higher than that of stoichiometric engines (λ > 10). However, diffusion controlled diesel combustion is predominately stoichiometric burn, in a microscopic sense, because the flames are prone to localise at approximately stoichiometric regions within the overall fuel lean but heterogeneous mixture. The prevailing flame temperature can be estimated with adiabatic stoichiometric flame temperature calculations (Heywood 2018).
A pressure-based algorithm for internal compressible turbulent flows through a geometrical singularity
Published in Numerical Heat Transfer, Part B: Fundamentals, 2019
Ali Nouri-Borujerdi, Ardalan Shafiei Ghazani
Downstream of the cross-section enlargement, the pressure of the compressible flow is almost constant up to a distance. This distance is an increasing function of the expansion ratio and is located between the enlargement cross-section to one half of the reattachment length. By increasing the expansion ratio, the minimum pressure of the flow and the distance at which the pressure is constant increases. Furthermore, Temperature increases slightly along the distance of constant pressure. Consequently, the density decreases through this region. Then, following the distance of constant pressure, density reaches a local maximum value. It is discovered that the fluid is heated by the expansion process and the outlet temperature is 5–7% greater than the inlet temperature for M = 0.6. Furthermore, increasing the expansion ratio beyond the D2/D1 = 4 would have a negligible effect on the outlet temperature.
Investigation on the similarity of turbine cascade with different working fluids
Published in Journal of Nuclear Science and Technology, 2022
Zhitao Tian, Ning Xu, Adil Malik
Figure 9 shows the expansion ratio contours in the middle section of the turbine cascade with different working fluids. As shown in Figure 9, compared with air and carbon dioxide, the starting point of helium expansion is closer to the leading edge of turbine blades and helium expands more fully. In other words, it is easier to obtain a larger expansion ratio by using a working fluid with a larger specific heat ratio. This is consistent with the result reflected in Figure 8(b).