Sketch of our phenomenological picture of flows of gas passing through a virial shock. The initial inflowing gas (in blue) is overdense relative to the halo gas at the boundary by a factor f (=ρ₀ ∕ρ_H or the stream density divided by the density of the ambient halo gas at the virial radius), shocks at the boundary between the intergalactic medium (labeled “IGM”) and the hot halo gas (labeled “halo”). The persistent virial shock and the higher pressure of the post-shock gas compared to the ambient halo gas, allows the flow to expand after being shocked (labeled “expansion”). If certain conditions are met, the post-shock gas becomes unstable, fragmenting to form a biphasic medium. The fragmentation enables a fraction of the initial momentumand energy of the stream to be captured as turbulent clouds of warm gas with a dispersion, σ_turb, and a volume-filling factor, ϕ_v,w. If the level of turbulence is high enough, the clouds move beyond the initial radius of the stream, decollimating the flow. Eventually, the hot post-shock gas mixes with the ambient halo gas which prevents it from cooling further. See text and the Appendix for definitions of the variables.