Base-flow characteristics of streams in the Valley and Ridge, Blue Ridge, and Piedmont physiographic provinces of Virginia

The separated base flow region within a linear aerospike nozzle segment is investigated experimentally in an ejector-diffuser system. The nozzle-diffuser system and base pressure characteristics are described over the pressure ratio range from the “open wake” to the “closed wake” operation. Schlieren photographs and static pressure distributions along the test section centerline and top contour describe the transition, from “open wake” to “closed wake” flow fields. Base pressure and static pressure distributions are utilized to present the effects of a ramp diffuser. The effects of base bleed on the base pressure ratio and structure of the nozzle flow field are also presented.

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Optimization of artillery projectiles base drag reduction using hot base flow

Thermal Science ◽

10.2298/tsci180413210d ◽

2019 ◽

Vol 23 (1) ◽

pp. 353-364

Author(s):

Mohammed Dali ◽

Slobodan Jaramaz

Keyword(s):

Drag Reduction ◽

Stokes Equations ◽

Flow Characteristics ◽

Turbulence Models ◽

Combustion Products ◽

Base Flow ◽

Navier Stokes ◽

Navier Stokes Equations ◽

Base Bleed ◽

Base Drag

The CFD numerical simulations were carried out to investigate the base drag characteristics of a projectile with base bleed unit with a central jet. Different base bleed grain types with different combustion temperatures were used. The goal was to find a way to effectively control the base flow for base drag reduction and optimisate the latter using an adequate CFD software. Axisymmetric, compressible, mass-averaged Navier-Stokes equations are solved using the k-? SST, transition k-kl-?, and RSM turbulence models. The various base flow characteristics are obtained by the change in the non-dimensionalized injection impulse. The results obtained through the present study show that there is an optimum bleed condition for all base bleed grains tested. That optimum is dependent on the temperature of the grain combustion products. The optimum reduces the total drag for 6,9% in the case of air injection at temperature of 300 K and reaches up to 28% in the case of propellant combustion products injection at almost 2500 K. Besides, the increasing of molecular weight has a role no less important than temperature of the combustion products in terms of base drag reduction.

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