PDPA only samples the very small droplets

[bphusted]

Describe the bug I have defined a spray using the Rosin-Rammler-lognormal distribution, where the droplet size varies between 1µm to about 400µm. Turning the particle diameter on in smokeview shows that the droplet varies from about 0.2µm to about 220µm, which is expected.

My PDPA device using D30 (M=3, N=0, mean volume droplet diameter) shows that the only droplets recorded are around 10µm. No droplets above 25µm are recorded, although I can see the droplets passing through the measurement volume in Smokeview.

To Reproduce Steps to reproduce the behavior:

1. Run the attached file:
   single_nozzle_turbulent_dis.zip
2. Open smokeview, load particles - > show/hide/particles/particle diameter. This will produce a similar figure as below, showing a relatively large variation in droplet size
3. Open the hist.csv file single_nozzle_turbulent_dis_hist.csv

Expected behavior I would have expected that the droplet size would vary from 1µm to 300µm, but only droplets around 10µm are recorded.

Screenshots

Desktop (please complete the following information):

• OS: Windows 10
• Version: [FDS 6.9.1] also tried it with earlier versions, down to 6.7.3, but got the same result.

Additional context Add any other context about the problem here.

[mcgratta]

I'll take a look.

[mcgratta]

I think you need this

&PROP ID='ROSIN-RAMMLER-LOGNORMAL_D30',
    PART_ID='water-drops_wm-7.1_9.9',
    QUANTITY='DIAMETER',
    PDPA_RADIUS=0.2,
    PDPA_START=3.0,
    PDPA_M=1,
    PDPA_N=3,
    HISTOGRAM=T,
    HISTOGRAM_NBINS=30,
    HISTOGRAM_CUMULATIVE=.FALSE.,
    HISTOGRAM_NORMALIZE=.TRUE.,
    HISTOGRAM_LIMITS=1.0E-6,500.0E-6 /

Note that PDPA_M=1 and PDPA_N=3. The User's Guide mentions this, but it is not too clear. I'll try to make it cleare.

[mcgratta]

Did my answer solve the problem?

[bphusted]

Thanks. I am still working on it.