This study proposes a comparison between CFD (Computational Fluid Dynamics) and experimental results for a cylindrical stirred tank reactor. The stirred tank reactor considered here is 0.7 m high, 0.4 m in diameter, baffled and has four impeller blades on a single shaft, placed at the symmetry axis. The tank is filled with water and serves as a model for molten aluminium purifying reactors.The experimental part of the study compares the use of PIV and LDV techniques to determine the flow field inside the tank. We use PIV to get a complete picture of the flow field in two vertical sections of the tank (one radial and one eccentric). LDV is then used to check and compare the velocities obtained by PIV along horizontal lines belonging to the two vertical sections considered under the PIVmeasurements. Good overall agreement between the two methods is obtained.The experimental results are compared to simulation of the tank using an alternative model that we have implemented in the commercial CFD software Fluent. The modeling approach we propose here avoids the classical sliding mesh technique and its tedious use (especially for pre-and post-processing). Our model does not physically represent the impeller blades. It rather introduces them as a time-dependent source term in the momentum equation. This term is only accounted for at the cells that would have been swept by a blade if the blades were present. The modeling of the tank and the set-up of the case are faster and easier. The computation of the flow field using this modeling approach is compared to the sliding mesh approach and to the experimental results discussed above. Results show good agreement between experimental data and both modeling approaches (sliding mesh technique and no impeller model). The model we propose does not bring more accuracy but more convenience in the modeling work.

A numerical method has been developed to predict the forced response of bladed disks due to a wake excitation from upstream blade rows. The structure is modeled by a three-dimensional finite element mesh of a bladed disk segment. Using cyclic symmetry, this model provides a modal base for the rotating structure. The aerodynamic damping of the vibratory modes and the excitation pressures on the blades due to the propagation of upstream flow defects are computed separately using the same three-dimensional unsteady Euler analysis software. A modal response solution of the aeromechanical system is then performed. This analytical methodology has been used to study the forced response of an experimental high pressure compressor blisk. The results are analyzed and compared with actual rig tests.

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SUMMARYThe serendipity (eight nodes) and Lagrange (nine nodes) plate elements following the Reissner±Mindlin irreducible formulation for the bending of plates are among the most popular in the ®nite element method. However, reduced integration on the shearing part of the stiness matrix has to be performed in order to avoid locking of the mesh in the limit of thin plates, where numerical constraints are taking some degrees of freedom in order to be satis®ed. This paper explains the competition between those constraints and the degrees of freedom, giving a mean to predict whether a mesh will lock or not. It also shows why the Lagrange element performs better than the serendipity element. Numerical results con®rm this analysis.

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