An improved particle tracking velocimetry(PTV) technique to evaluate the velocity field of saltating particles

Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photographs is quite laborious. However, particle tracking velocimetry（PTV） can be used to measure the instantaneous velocity in fluids using tracer particles. The tracer particles have three basic features in fluids： similar movement patterns within a small region, a uniform particle distribution, and high particle density. Unfortunately, the saltation of sand particles in air is a stochastic process, and PTV has not yet been able to accurately determine the velocity field in a cloud of blowing sand. The aim of the present study was to develop an improved PTV technique to measure the downwind（horizontal） and vertical velocities of saltating sand. To demonstrate the feasibility of this new technique, we used it to investigate two-dimensional saltation of particles above a loose sand surface in a wind tunnel. We analyzed the properties of the saltating particles, including the probability distribution of particle velocity, variations in the mean velocity as a function of height, and particle turbulence. By automating much of the analysis, the improved PTV method can satisfy the requirement for a large sample size and can measure the velocity field of blowing sand more accurately than previously-used techniques. The results shed new light on the complicated mechanisms involved in sand saltation.

Atomization parameters of coal water paste measured by PIV technique

The particle image velocity (PIV) technique is introduced to measure theatomization angle, particle size and size distribution of the atomization coal water paste (CWP) ina cold state model. Due to high-density atomization spray, wide size distribution and large-scaleexperimental setup in CWP experiments, a commercial PIV system is updated with a 600-mm-long focallength camera and a convex lens used with a laser beam. This long focal length camera makes the PIVsystem capable of taking the images of micro particles. The measured minimum diameter is about 15μm. The convex lens has the benefit of centralising the sector laser beam of the PIV system, sothat the measurement window of the high density CWP field sectored by the laser beam is brighter andthe images taken by the camera are clearer. The experimental results show that it is a useful andefficient tool for the PIV technique to measure the atomization prosperities of CWP.

Particle image velocimetry measurement of velocity distribution at inlet duct of waterjet self-propelled ship model

A vehicle-mounted three-dimensional underwater particle image velocimetry（PIV） device is used in a towing tank to measure the velocity distribution of the inlet duct of a waterjet ship model in a self-propulsion test. The following points are shown through a comparison of the influences of the stationary and free states of the ship model on the measured results：（1） during the test, the ship attitude will change, specifically, the ship model will heave and trim,（2） the degree of freedom disturbs the processing of the pixel images enough to distort the subsequent image processing,（3） the stationary state of the ship model is the optimal mode for measuring the velocity distribution using the PIV device, and（4） if the changes must be considered, the man-made heaving and trimming may be pre-applied, and be made a corrected stationary mode. In addition, the momentum effect coefficient and the energy effect coefficient are calculated in a non-uniform inflowing state, and the related factors affecting the two coefficients are analyzed. The test results show that the pumping action of the waterjet creates a transverse vector in the cross-sectional speed, which increases the non-uniformity of the inflow. These results could help to establish the design requirements for a waterjet-propelled ship type.

Internal Flow Field Measurement of Gas Turbine Based on Optical Flow Method

The in-cylinder flow field of the internal combustion engine is an important factor affecting the quality and combustion quality of the fuel mixture in the cylinder. In order to calculate the high-precision flow field, the paper presents a flow field calculation method based on the optical flow algorithm. The motion of the point was calculated using the change in pixel intensity within two temporally adjacent frame images. The results show the high accuracy and resolution of the flow field at small displacement conditions.

Ultrasound Imaging Signal Analysis of Underwater Topography in River Model Experiment

In this paper, we analyze the feature of ultrasonic image and investigate the effect of topography material, flow velocity and sediment concentration on the imaging of underwater topography by imaging experiments of model sands. These imaging experiments are conducted in river engineering physical model.The results show that the vertical distribution of pixel values is changed hugely at the position of imaging bright band of underwater topography. The imaging of underwater topography is not affected when flow velocity is below 40 cm/s and sediment concentration is below 5.0 ‰. The main influence factors of imaging signals are flow velocity and sediment concentration near the topographical bed. The resolution of ultrasound imaging signals is high, and the topography consisted of model sands with particle size smaller than 0.1 mm can be monitored well in the river model experiment.