RMS velocities
by
Atle Lohrmann
—
last modified
Aug 17, 2007 09:11 AM
Hi
Our background in fluid mechanics here at Nortek is not very strong and I am not quite sure I know what "integral time scale is". However, it seem quite reasonable that the RMS values will decrease as you go from 25 to 1 Hz sampling. The internal sampling rate is the same in both cases so the effect of the decreased sampling rate is increased averaging of both the turbulence and the instrument noise.
Our background in fluid mechanics here at Nortek is not very strong and I am not quite sure I know what "integral time scale is". However, it seem quite reasonable that the RMS values will decrease as you go from 25 to 1 Hz sampling. The internal sampling rate is the same in both cases so the effect of the decreased sampling rate is increased averaging of both the turbulence and the instrument noise.
| Quote |
Hi there, I am measuring the flow in an axi-symmetric jet. I get a right mean flow, but my RMS velocities are higher than what it should be when I sample at 25Hz. If I set the sampling freq to 1Hz, I get lower RMS values. I also used different filters, but they did not change the results. I calculated my integral time scale from the data sampled at 25Hz and when I sample at the integral frequency I get correct RMS velocities. I cannot figure out the reason. Maybe this is a coincidence. When there is no mean flow, and only turbulence exists, the sampling frequency does not affect the turbulence statistics. So I think my problem has got something to do with the mean flow. Thanks for your helps in advance. |
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