  A radiatively inefficient accretion flow (RIAF), which is commonly
characterized by its sub-Keplerian nature, is a favored accretion model for the
supermassive black hole at Galactic center, Sagittarius A$^{*}$. To investigate
the observable features of a RIAF, we compare the modeled shadow images,
visibilities, and spectra of three flow models with dynamics characterized by
(i) a Keplerian shell which is rigidly-rotating outside the innermost stable
circular orbit (ISCO) and infalling with a constant angular momentum inside
ISCO, (ii) a sub-Keplerian motion, and (iii) a free-falling motion with zero
angular momentum at infinity. At near-mm wavelengths the emission is dominated
by the flow within several Schwarzschild radii. The energy shift due to the
flow dynamics becomes important and distinguishable, suggesting that the flow
dynamics are an important model parameter for interpreting the mm/submillimeter
very long baseline interferometric observations with the forthcoming, fully
assembled Event Horizon Telescope (EHT). As an example, we demonstrate that
structural variations of Sagittarius A$^{*}$ on event horizon-scales detected
in previous EHT observations can be explained by the non-stationary dynamics of
a RIAF.
