| 86 | | Ultrasonic velocimetry profiling (UVP) is a technique that measures a single component of velocity at either 128 or 256 points along a line. A transducer sends out an ultrasonic pulse, and then gates the return signal into a series of spatial bins. The individual transducers can be multiplexed in order to provide pseudo-velocity fields. The transducers are linked via a multiplexer with a delay of 15 ms, so the two-dimensional velocity field is not instantaneous, however velocity fields can be collected at 3-4 Hz. Two frequencies of transducers will be used. An array of ten 4 MHz UVP probes (with 10 m long cables) will be used for collecting downstream velocity profiles, these probes are positioned at heights (centre point of each probe) of 7, 16, 26, 56, 86, 116, 146, 176, 206 and 236 mm from the base of the channel. These probes are positioned in a custom made plastic holder, in turn connected to a bar strapped to the channel top. Initially, the probes are positioned on the channel centreline, 80 mm downstream of the apex of bend 2, looking upstream. An array of ten 2 MHz UVP probes (with 4 m long cables) will be used to examine the nature of secondary flow at bend apices. This involves drilling holes in the apexes of bends 1 and 2 and inserting the UVP probes. Probes will have to be moved between experiments, to look at the two different bend apexes. 2 Mhz probes are required for the cross-section measurements since the measurement range needs to be much larger (60 cm) than is required for the axial velocity measurements. |
| | 86 | Ultrasonic velocimetry profiling (UVP) is a technique that measures a single component of velocity at either 128 or 256 points along a line. A transducer sends out an ultrasonic pulse, and then gates the return signal into a series of spatial bins. The individual transducers can be multiplexed in order to provide pseudo-velocity fields. The transducers are linked via a multiplexer with a delay of 15 ms, so the two-dimensional velocity field is not instantaneous, however velocity fields can be collected at 3-4 Hz. Two frequencies of transducers will be used. An array of ten 4 MHz UVP probes (with 10 m long cables) will be used for collecting downstream velocity profiles, these probes are positioned at heights (centre point of each probe) of 7, 16, 26, 56, 86, 116, 146, 176, 206 and 236 mm from the base of the channel. These probes are positioned in a custom made plastic holder, in turn connected to a bar strapped to the channel top. Initially, the probes are positioned on the channel centreline, 80 mm downstream of the apex of bend 2, looking upstream. An array of ten 2 MHz UVP probes (with 4 m long cables) will be used to examine the nature of secondary flow at bend apices. This involves drilling holes in the apexes of bends 1 and 2 and inserting the UVP probes. Probes will have to be moved between experiments, to look at the two different bend apexes. 2 MHz probes are required for the cross-section measurements since the measurement range needs to be much larger (60 cm) than is required for the axial velocity measurements. |
