A priori testing is an important tool in LES modeling. It allows to test, at the core, the validity of the assumption of a given SGS model. In the present work we intend to examine the alignment between SGS stresses and strain in the case of an annular duct subject to differential heating, as a step into the development of a LES methodology in boundary fitted coordinates apt to simulate buoyancy-related phenomena. Thus the simulation flow in a concentric annular channel with differential heating at the walls has been conducted. The buoyancy contribution to the momentum equation has been modeled through the Boussinesq approximation. The code employed is based on the boundary fitted coordinates framework and the fractional step algorithm. The pressure equation is solved using a pseudo-spectral method in the stream-wise direction. The convective term has been discretized through fourth-order schemes and advances temporally through a second order scheme. The agreement with available experimental data was found overall good. A database of instantaneous snapshots of the flow field has then been collected. The flow filed has been filtered spatially and the assumptions of the LES models under examination have been tested.