Ultrasound flow mapping of complex liquid metal flows with spatial self-calibration

Investigating the complex interaction of electrically conductive fluids and magnetic fields is relevant for a variety of applications from basic research in magnetohydrodynamics (MHD) to modeling of industrial processes involving metal melts, such as steel casting and crystal growth. However, experimental studies in this field are often limited by the performance of flow instrumentation for opaque liquids. Commercially available measurement systems usually lack the ability to provide a time-resolved imaging of transient flow structures. We present an ultrasound array Doppler velocimeter (UADV) for flow mapping in opaque liquids near room temperature. It is modular and flexible regarding its measurement configuration, for instance it allows capturing two velocity components in two planes (2d–2c) of 67×67 mm² with a frame rate of 30 Hz. It uses up to 9 linear arrays with 25 ultrasound transducers each driven in a parallelized time division multiplex (TDM) scheme. A FPGA-based signal processing allows a continuous realtime operation of the measurement system. Combining the single-component velocity data of each linear array to a 2d–2c flow field demands precise knowledge of the relative geometric position of the transducer arrays. We present a novel method that performs a spatial self-calibration by a mutual time of flight measurement, significantly reducing alignment errors. A measurement example of a magnetically stirred flow of GaInSn in a rectangular container is given. The UADV is applied to experiments in the context of manufacturing crystalline silicon ingots for photovoltaics.     

电气传动系统PID自适应控制研究

本文利用神经网络组成的PID自适应控制器,对一大变负载电气伺服系统进行控制,仿真与实验表明：该控制器优于一般伺服控制器的性能并具有较强的鲁棒性。     

Use of gas bubbles for ultrasound Doppler flow velocity profile measurement

Ultrasonic velocimetry based on the Doppler shift effect accurately provides quasi-instantaneous flow fields for fluids with a sufficiently high acoustic scattering level. However, ultrasonic velocity instruments are known to perform poorly in clear water with low acoustic scattering level, which are frequent conditions in laboratory applications. This work confirms a technique to solve the problem by seeding the flow with micro hydrogen bubbles, generated by means of electrolysis.This paper investigates the influence of gas bubbles density on the quality of the ultrasound Doppler based velocity profiles in an open channel flow. The bubbles are generated by electrolysis of water using different magnitudes of electrical current. The estimation of the number of bubbles in the measurement volume confirms that the bubble diameter is similar to that of the wire used for electrolysis. This enables to determine the minimum density of gas bubbles needed to obtain a reasonably good echo and therefore an accurate velocity profile.     

Pressure field estimation from ultrasound Doppler velocity profiler for vortex-shedding flows

A novel algorithm of pressure field estimation based on ultrasound velocity profiler (UVP) is developed. The method consists of UVP measurement of velocity distribution in fluid flows and numerical analysis of the measured data using fluid dynamics equations. We introduce equation of continuity, incompressible Navier-Stokes equation and proper orthogonal decomposition (POD) into the basic algorithm, so that pressure field of space-time two-dimensional unsteady fluid flow is fully reconstructed. Since UVP is based on ultrasound Doppler principle, the local instantaneous pressure distribution is obtained non-intrusively. The performance of an algorithm is evaluated for vortex shedding flow behind a circular cylinder at Re = 1000. Considering the specification of UVP, the optimal method of experimental data conversion to pressure information is proposed. We have found that the one-dimensional velocity measurement by UVP upon Taylor's frozen hypothesis is suitable for evaluation of pressure field in wake of the cylinder. The present algorithm is also demonstrated for opaque fluid flows by considering vortex flow in milk.     

Viscoelastic responses of flow driven by a permeable disk investigated by ultrasound velocity profiling

Ultrasound velocity profiling was applied to viscoelastic flow induced around a moving permeable disk. There were two objectives to this measurement. The first was to find technical advantages and restrictions when applying ultrasonic Doppler velocimetry to a viscoelastic liquid. This issue has not been clarified even though ultrasonic pulses may interact with an elastic medium in the monitoring of the Doppler shift frequency. The second objective was to determine the fluid physics of a viscoelastic liquid around a permeable object, which will help in designing mixing process for materials subject to strong rheological resistance. In this paper, we report a representative response of a viscoelastic liquid in terms of its spatiotemporal velocity distribution. The response highlighted is cyclic lateral waves that form behind the disk, which were hardly detectable by particle image velocimetry. We discuss multiple reasons for this phenomenon considering not only fluid properties but also the measurement principle of ultrasound velocity profiling as applied to viscoelastic liquid.