Debris Shielding during High-speed Erosion

Monte Carlo analysis of wall erosion and direct contact heat transfer by impinging two-phase jets

“…Assumption 1 is valid when Af m is smaller than the time between collisions and larger than the collision's duration, and assumption 2 is valid provided that the cell is so small that the spatial variation of flow variables in the cell is negligible. Idea 3 of the DSMC method is usually unnecessary for suspension flow because of relatively small particle number densities; its validity follows from the invariance of the Boltzmann equation (8) to the scaling transformation.…”

“…The discontinuity in R arises from the foregoing stipulation that friction does not reverse the slip velocity between the particles. If we apply this collision dynamics model and the assumptions just listed, the Boltzmann equation for the particle distribution function in a mixture of s particle types may be derived following the standard procedure, 13 yielding a set of coupled transport equations Z f J=>IJW,JQ (8) where/ =/(r,r,/) is the distribution function for particles of type /; r is a position vector, / the time; F/m the particle acceleration resulting from body forces and gas friction; S,{v 9 r 9 t) the external source term for particles of type /; the velocities v' and v\ are related to v and v l by Eq. 3; o tj is the collision cross section, given as n(d t + dJ) 2 /4 for a collision between particles of types i and j; dQ is the differential solid angle; W v is the domain in the space of velocities.…”

“…A similar trend has been observed in the erosion of a blunt body transversing a rain field. 8 This behavior may be attributed to interparticle collisions. The attacking particles, before impinging on the surface, must penetrate a "cloud" of rebounding particles and debris.…”

“…Therefore, rebounding particles near the eroded surface may be regarded as shielding it, in a manner similar to debris shielding ascribed to the high-speed erosion of bodies in a rain field. 8 Moreover, experimental investigations of the brittle erosion mode have indicated that maximal surface erosion by particle-laden jets did not occur at an incidence angle of 90 deg, although .the brittle erosion by a single particle should be maximal at this angle; it has been surmised that at this angle there is considerable interference of incident particles with rebounding particles, hence, the reduced erosion. 9 In addition to the particles' incidence angle, the following parameters reportedly have increased the effect of particle concentration on the erosion rates 7 : the impact velocity, strength of the abrasive particle, and particle size.…”