Про раздув грунта под ЛМ и "Луной"

The findings of this investigation suggest that the
extent of surface erosion accompanying LEM descent engine exhaust gas
impingement upon the lunar surface will probably not be
sufficient to create conditions which are hazardous to the lunar
landing. That is, for particles of 0.1 inch diameter or less
possessing physical properties similar to those assumed in these
calculations, the predicted erosion depth at the landing pad
contact sites is only a fraction of one foot, even for the case
of low velocity (one ft/sec) descent. The premise in this study
was that though Roberts' analytical model is inapplicable near
the jet center-line for low nozzle exit-plane to surface distances,
it should over-estimate the situation in general and furnish a
reasonable first estimate of the true situation at the larger
radial distances at which the landing-pads are deployed. It is
imperative, however, that additional experimental data on erosion
be obtained in the "near surface" regime, e.g., nozzle exit-plane
to surface distances of ten feet or less.

 

The exhaust flow field of a jet is depicted schematically in a plane section taken through the jet axis in figure 1. Since the moon is believed to be practically devoid of any atmosphere, the jet will operate in an "underexpanded" condition; that is, the static pressure at the jet exit will greatly exceed any
ambient pressure. Under such conditions, the jet plumes out, or expands, at a very large angle with respect to the jet axis. Most of the energy, however, is confined to a narrow core as evidenced from the pressure data in reference ll. Also under these high expansions no transverse or oblique shock waves are formed
in a free jet. Just above the surface, a bowl-shaped shock occurs which turns the flow radially outward. Where the extended axis of the jet intersects the surface, a stagnation condition exists. The static pressure along a radial line on the surface decreases rapidly from the stagnation pressure as radial distance from the stagnation point increases. The flow just above the surface boundary layer is accelerating radially from zero speed at the stagnation point and reaches supersonic speeds while continually
decreasing in density. At at top of boundary some radial location a condition of maximum dynamic pressure
is reached. At this location the maximum surface shearing stress is likely to occur. Thus, the dust may be expected to erode initially in an annular ring as verified experimetally in references 11 and 13. With a low
nozzle height, the erosion should extend radially with time both inward and outward from the initial ring. The
dust ejected from the crater will move upward and outward in a sheet which, near the surface, resembles an
inverted and truncated cone.