| 72 | | '''Ultrasonic Velocimetry Profiling (UVP)''' Ultrasonic velocimetry profiling (UVP) is a technique that measures a single component of velocity at up to several hundred 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. A UVP-duo was used, with two different frequencies of transducers. An array of ten 4 MHz UVP probes (with 10 m long cables) was used for collecting downstream velocity profiles. Initial test experiments used probes positioned at heights of (centre point of each probe): 7, 16, 26, 56, 86, 116, 146, 176, 206 and 236 mm. The actual experiments used probes are positioned at heights (centre point of each probe) of 10, 25, 50, 75, 100, 150, 200, 250, 350 and 450 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) is used to examine the nature of secondary flow at the second bend apex. This involves drilling holes in the apex of bend 2 and inserting the UVP probes. The probes are positioned at heights of 45, 90, 135, 180, 225, 270, 315, 360, 404, and 450 mm from the base. 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. |
| | 72 | '''Ultrasonic Velocimetry Profiling (UVP)''' Ultrasonic velocimetry profiling (UVP) is a technique that measures a single component of velocity at up to several hundred 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. A UVP-duo was used, with two different frequencies of transducers. An array of ten 4 MHz UVP probes (with 10 m long cables) was used for collecting downstream velocity profiles. Initial test experiments used probes positioned at heights of (centre point of each probe): 7, 16, 26, 56, 86, 116, 146, 176, 206 and 236 mm. The actual experiments used probes positioned at heights (centre point of each probe) of 10, 25, 50, 75, 100, 150, 200, 250, 350 and 450 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) is used to examine the nature of secondary flow at the second bend apex. This involves drilling holes in the apex of bend 2 and inserting the UVP probes. The probes are positioned at heights of 45, 90, 135, 180, 225, 270, 315, 360, 404, and 450 mm from the base. 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. |
