  We present three-dimensional local hydrodynamic simulations of flows around
objects embedded within stellar envelopes using a "wind tunnel" formalism. Our
simulations model the common envelope dynamical inspiral phase in binary star
systems in terms of dimensionless flow characteristics. We present suites of
simulations that study the effects of varying the binary mass ratio, stellar
structure, equation of state, relative Mach number of the object's motion
through the gas, and density gradients across the gravitational focusing scale.
For each model, we measure coefficients of accretion and drag experienced by
the embedded object. These coefficients regulate the coupled evolution of the
object's masses and orbital tightening during the dynamical inspiral phase of
the common envelope. We extrapolate our simulation results to accreting black
holes with masses comparable to that of the population of LIGO black holes. We
demonstrate that the mass and spin accrued by these black holes per unit
orbital tightening are directly related to the ratio of accretion to drag
coefficients. We thus infer that the mass and dimensionless spin of initially
non-rotating black holes change by of order $1\%$ and 0.05, respectively, in a
typical example scenario. Our prediction that the masses and spins of black
holes remain largely unmodified by a common envelope phase aids in the
interpretation of the properties of the growing observed population of merging
binary black holes. Even if these black holes passed through a common envelope
phase during their assembly, features of mass and spin imparted by previous
evolutionary epochs should be preserved.
