Particle Image Velocimetry is getting more and more often the method of choice not only for visualization of turbulent mass flows in fluid mechanics, but also in linear and non-linear acoustics for non-intrusive visualization of acoustic particle velocity. Particle Image Velocimetry with low sampling rate (about 15Hz) can be applied to visualize the acoustic field using the acquisition synchronized to the excitation signal. Such phase-locked PIV technique is described and used in experiments presented in the paper. The main goal of research was to propose a model of PIV systematic error due to non-zero time interval between acquisitions of two images of the examined sound field seeded with tracer particles, what affects the measurement of complex acoustic signals. Usefulness of the presented model is confirmed experimentally. The correction procedure, based on the proposed model, applied to measurement data increases the accuracy of acoustic particle velocity field visualization and creates new possibilities in observation of sound fields excited with multi-tonal or band-limited noise signals.
This study is concerned with liquid flow induced by a disk which rotates steadily around its axis and touches the free surface of liquid contained in a cylindrical vessel. It is a simplified model of the flow in the inlet part of a vertical cooling crystallizer where a rotary distributor of inflowing solution is situated above the free surface of solution contained in the crystalliser. Numerical simulations of flow phenomena were conducted and the simulation results were interpreted assuming an analogy with Kármán’s theoretical equations. In a cylindrical coordinate system, the components of flow velocity were identified as functions of distance from the surface of the rotating disk. The experimental setup was developed to measure velocity fields, using digital particle velocimetry and optical flow. Conclusions concerning the influence of disc rotation on liquid velocity fields were presented and the experimental results were found to confirm the results of numerical simulation. On the basis of simulation data, an approximation function was determined to describe the relationship between the circumferential component of flow velocity and the distance from the disk.
Maximum Torque Control (MTC) is a new method applied for control of induction motor drives. The drive is controlled by dc voltage supplying a converter in the range below nominal speed and by a field that weakens for a speed range above the nominal speed. As a consequence, the control is quite similar to the control of a classical separately excited dc motor. This control method could be explained as a kind of sim- plification of Direct Torque Control (DTC), because the switching scheme is the same as for the DTC, but the variable responsible for a torque control is constantly set for “torque increase”. This kind of control of induction motor drive is simpler than DTC because torque values need not be estimated. The proposed control method offers very good performance for 3-phase induction motors and requires smaller switching frequency in comparison to DTC and Field Oriented Control (FOC). The application of the con- trol is widely demonstrated for a 3-phase 315 kW, 6 kV motor drive by use of computer simulation.