Technique

UDV 2D/3D

2D/3D Ultrasonic velocimetry

Background

2D or 3D Ultrasonic Doppler Velocimetry measuring technique is a method that enables the measurement of two velocity components (U and W) or three velocity components (U,V and W) simultaneously along a line.

UDV-2D and UDV-3D have all the advantages of classical ultrasonic Doppler velocimetry, such as the capacity to realize measurements in non translucid liquids. One of the most interesting property of these techniques compared to other techniques that can measure simultaneously more than one velocity component is its real time feature. Only a few tens of milliseconds are necessary to compute and display a complete set of 2D or 3D velocity profile.

2D transducers setup for ultrasonic Doppler velocimetry

2D transducers setup

UDV-2D is based on a 3 transducers system. Only one transducer is used as an emitter. The two others are used as receivers.

For UDV-2D measurements the three transducers are arranged as displayed in figure beside. The two receivers are placed on each side of the emitter and at the same distance from it. All ultrasonic beams axis cross at the same point and are contained in the same plane.

The centers of the piezos of these three transducers are not necessarily aligned on the X-axis. This arrangement allows to measure velocities along the ultrasonic beams of the emitter in many points. The depths over which measurements are available depend on the geometry of the ultrasonic beam of the transducers, on their distances between each other and on the receivers angle (the angle between the emitter's beam and one of the receiver's beam).

Each set of emitter-receiver gives one velocity component. These components are processed by UDOP software which gives the velocity components in the Cartesian coordinate system.

3D transducers setup

For UDV-3D measurements, the same kind of arrangement is used as in 2D, as shown in the figure. A central transducer is used to emit ultrasonic bursts and three lateral transducers, placed uniformly (at 120 degrees) around the emitting transducer, are used to receive the echoes. The centers of the piezos of these four transducers are not necessarily within the same XY-plane.

Each set of emitter-receiver gives one velocity component. These components are processed by UDOP software which gives the velocity components in the Cartesian coordinate system.

3D transducers setup for ultrasonic Doppler velocimetry
Sampling volume and spatial resolution in UDV 2D/3D

UDV 2D/3D spatial resolution

In UDV 2D/3D the definition of the lateral dimensions of the sampling volume is not as simple as in 1D. This results mainly from the different ways the ultrasonic beams interact with each other. Emitting on one transducer and receiving the echoes from another one means that the location of the centers of the sampling volumes and their radial dimension change over the measuring depths.

As UDV 2D/3D uses 2 or 3 couples emitters-receivers, for a defined depth, more than one sampling volumes will be involved. Therefore, correct measurements will be available only if the flow field in each sampling volume is identical. In such a case, the sampling volumes corresponding to a particular depth, can be combined in a unique one, called global sampling volume, which has a much bigger dimension than in 1D.

UDV 2D/3D simulation software

As it is of prime importance to setup correctly the probes, a simulation software is offered to help the selection of the geometry, the type of transducers and the operating parameters for UDV-2D and UDV-3D measurement. This software also allows to simulate the 1D behavior.

The flow is simulated by a single source of particles, which emits particles in all directions. The flow pattern is defined by the position of the source of particles, and the velocity range is fixed by the velocity at which particles are ejected from the source.

The simulation tool gives an idea of the lateral dimension of the global sampling volume (green border in the figure). It can compare the velocity measurement based on the movement of the particles and the real velocity at which the particles are traveling.

It shows also the influence of the parameters such as the angle of the receivers.

UDV 2D/3D simulation software output