Open Access

We have investigated the acoustic properties of silicon dioxide thin films. Therefore, we determined the phase velocity dispersion of LiNbO3 substrate covered with SiO2 deposited by a plasma enhanced chemical vapor deposition and a physical vapor deposition (PVD) process using differential delay lines and laser ultrasonic method. The density p and the elastic constants (c11 and c44) can be extracted by fitting corresponding finite element simulations to the phase velocities within an accuracy of at least ±4%. Additionally, we propose two methods to improve the accuracy of the phase velocity determination by dealing with film thickness variation of the PVD process.

Pump impellers have to be designed from two separate points of view. From a hydraulic aspect the impeller has to fulfill the specified operating conditions for flow rate, head at the speed of rotation. Additionally, from the structural point of view, the impeller must be capable to resist mechanical loads. To fulfill nowadays requirements of flexible operating conditions, the mechanical design becomes more crucial, because of increased loads at part-load operation. Consequently, trustworthy information about deformation and stress are mandatory. The present paper deals with the comparison of mechanical deformation of a pump impeller at design and off-design operation. The full loading on the impeller caused by fluid pressure and centrifugal forces is considered in experimental and numerical investigations. Therefore, an experimental model pump, representing a repeating stage of a multistage boiler feed pump has been developed. Besides performance values, transient pressure and strain measurements at the back side of the impeller rear shroud are evaluated. For the strain measurements, strain gauges are used in Wheatstone bridges to evaluate transient data. For numerical simulations a one-way coupled Fluid Structure Interaction (FSI) model has been used. Transient Computational Fluid Dynamics (CFD) simulations have been performed for the complete model pump. For the turbulence modeling Menter’s SST model was used. In subsequent quasi-stationary Finite Elements (FE) simulations, the pressure loading on the impeller is taken from the CFD simulations for one impeller revolution.