  Consider the Navier-Stokes flow past a rotating obstacle with a general
time-dependent angular velocity and a time-dependent outflow condition at
infinity. After rewriting the problem on a fixed domain, one obtains a
non-autonomous system of equations with unbounded drift terms. It is shown that
the solution to a model problem in the whole space case $\R^d$ is governed by a
strongly continuous evolution system on $L^p_\sigma(\R^d)$ for $1<p<\infty$.
The strategy is to derive a representation formula, similar to the one known in
the case of non-autonomous Ornstein-Uhlenbeck equations. This explicit formula
allows to prove $L^p$-$L^q$ estimates and gradient estimates for the evolution
system. These results are key ingredients to obtain (local) mild solutions to
the full nonlinear problem by a version of Kato's iteration scheme.
