Ram pressure in astronomy and engineering

Abstract

The ram pressure of a moving fluid, P r , is the rise in pressure at a stagnation point relative to the upstream pressure. In astronomy, it is used to calculate the interaction of stellar winds with planets and to quantify the effects of ram pressure stripping. On aeroplanes and in wind tunnels, it is measured with a pitot-static tube, an inexpensive device with no moving parts that was invented in 1732. Up through the mid-1960s, across both astronomy and engineering the ram pressure of a moving gas and its momentum flux, ρ u 2 , where ρ and u are the upstream mass density and flow speed, were properly treated as related but distinct quantities. This relationship may be expressed as P r = Sp ρ u 2 , where Sp is the dimensionless Spreiter number, which ranges between 0.5 and 0.88 for a monatomic gas, depending on the upstream Mach number, Ma . Unfortunately, by the early 1970s, in astronomy ram pressure was defined to be the momentum flux and Sp was fixed to be unity and forgotten as a parameter. This article seeks to raise awareness of this issue, and to review the determination of Sp for subsonic and supersonic flow.

Revolutionizing astronomy: Technological advancements and future horizons

“…The James Webb Space Telescope, set to be launched, represents a breakthrough in infrared astronomy. With its advanced instruments and unprecedented sensitivity, it is expected to revolutionize our understanding of the universe's early stages, shedding light on the formation of galaxies, stars, and planetary systems [6]. By observing the universe in the infrared spectrum, the JWST is poised to make groundbreaking discoveries that will reshape our comprehension of cosmic evolution.…”