Bow shocks

Shock in rotor losses. This loss is due to shock occurring at the rotor inlet. The inlet of the rotor blades should be wedgelike to sustain a weak oblique shock, and then gradually expanded to the blade thickness to avoid another shock. If the blades are blunt, a bow shock will result, causing the flow to detach from the blade wall and the loss to be higher. 

The formation of a shock wave is dependent on the objects that affect the flow field. The conservation of mass, momentum, and energy must be satisfied at any location. This is manifested in the formation of a shock wave at a certain location in the flow field to meet the conservahon equations. In the case of a blunt body in a supersonic flow, the pressure increases in front of the body. The increased pressure generates a detached shock wave to satisfy the conservation equations in the flow field to match the conserved properties between the inflow and outflow in front of the body. The velocity then becomes a subsonic flow behind the detached shock wave. However, the shock wave distant from the blunt body is less affected and the detached shock wave becomes an oblique shock wave. Thus, the shock wave appears to be curved in shape, and is termed a bow shock wave, as illustrated in Fig. C-1. 

Figure C-1. A bow shock wave formed in front of a blunt body.

Early on it was proposed that Jovian resonances could excite planetesimal eccentricities enough to cause collisional disruption and melting of dust by bow-shocks in the nebular gas (Weidenschilling el al. 1998). Follow-on work showed that planetesimals with a radius of 1000 km and moving at least 8 km s-1 with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates consistent with those inferred for chondrules (Ciesla et al. 2004). 

A major problem for the shock model has been to find a source of powerful, pervasive, and repeatable shocks. Several have been proposed clumpy material falling into the nebula (Tanaka et al, 1998), bow shocks from planetesimals scattered by Jupiter (Hood, 1998 Weidenschillingetal., 1998), and spiral-arm instabilities in the solar nebula (Wood, 1996b). Boss infers that clumps and spiral arms could generate 10kms shocks in the asteroid belt (Chapter 1.04). lida et al. (2001) and... 

Hood L. (1998) Thermal processing of chondrule precursors in planetesimal bow shocks. Meteorit. Planet. Sci. 33, 97-107. 

ACC-4 still has about 3-4% voids and fissures, which are detrimental to the performance of the material. In its use as a missile nose cone or rocket nozzle, the extremely hot gas environment can result in rapid degradation of the part because the chemically reactive gases can rapidly permeate the structure via the interconnecting fissures and voids and attack the carbon fibers. Furthermore, in the bow shock wave of a missile nose cone that reenters the ionosphere, the atomic oxygen that is formed can similarly permeate and attack the fibers. Further densification of ACC-4 by another PIC cycle (to reduce the voids to below the 3% level) is virtually impossible because the resin or pitch cannot be forced into the microcracks and pores of the composite even under extremely high hydrostatic pressure of 700-1,500 bar, because of viscosity and surface tension considerations. 

Figure 7 shows the distributions of the center-line Mach number under vacuum and four different back pressures of 7, 15, 25, and 35 kPa. As shown in this figure, the early bow shocks reduce the Mach number slightly below unity. Then, the flow experiences a series of expansion/compres-sion waves along the nozzle. 

The earth manifests its presence in the solar wind in a manner analogous to that of a supersonic airplane traversing the atmosphere. Since the solar wind velocity is faster than the characteristic speed in the ionized gas, a shock wave (the bow shock) is established. The average location of the shock is some 10-14 earth radii outward on the sunward side (Fig. 3). On the earthward side of the shock wave is a region of more turbulent solar wind flow, the magnetosheath. Then, at an average altitude above the earth of some nine earth radii, the magnetopause exists... 

As shown in Fig. 1, a spherical body of radius R is initially placed in a supersonic gas flow whose parameters are R y p U, and the Mach number Ml Bow-shock wave SWi is situated at a distance 6 in front of the body on the axis from the frontal point. 

Explosive Desensitization by Jet Bow Shock Wave - NOBEL Calculation FEFEHE.MVE - Steel Jet/Steel Barrier/Comp B - Forest Fire JETMSFF.MVE - Steel Jet/Steel Barrier/Comp B - MSFF... 

Moreover, the line profiles are consistent with models of bow shocks e.g. Hartigan et al., 1987), seen with a range of projection angles. The line width ves the shock velocity in such models, yielding the speed of the bullet and time since ejection. The [FeII line ratios are typical of collisional excitation in gas of electron density 10 cm. The overall spectrum is characteristic of excitation in fast (> lOOkm/s), dissociative J-shocks e.g. HoUenbach McKee, 1989), although some detailed differences await explanation, such as the weakness of the [Cl] and [N lines. This may in part be due to the shock speeds being hi er than has been modelled. 

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