A High Elevation Aerosol Inlet Modeling Study and Inter-comparisonA. Gannet Hallar1, Ian McCubbin1, Igor Novosselov2, Riley Gorder2, John Ogren3

1: DRI – Storm Peak Laboratory 2:Enertechnix, Inc. 3:NOAA-ESRL-GMDL

oNumerical wind tunnel : inlet 1m x 1m oTotal in wind tunnel ~ 5,000,000 cells

oWind speeds: 2.5 -15 m/soParticle sizes: 10nm – 20micron

Computational Domain

DRI - SPL

Modeling of Current Inlets - 1000 lpm

DRI - Storm Peak Laboratory, CO

NOAA, DOE ARM networks multiple locations

JungfraujochTypical sampling rate 200 lpm

Effects of Wind Speed and Particle Size.

NOAA Jungfraujoch

Factors in Sampling Efficiencyηsampling = ηaspiration * ηtransmission

Aspiration efficiency related to isokinetic sampling (velocity mismatch, sampling orientation), free stream turbulence

Transmission efficiency – internal losses due to: inertial impaction, turbulent dispersion, gravitational settling, electrostatic interaction

Abstract - A51A-0016. This study presents a comparison of three high volume aerosol inlets used for atmospheric sampling at various sites, including the Desert Research Institute’s Storm Peak Laboratory, the Sphinx Laboratory at Jungfraujoch (Switzerland), and the design commonly used by NOAA’s Global Monitoring Division and the Department of Energy’s Atmospheric Radiation Measurement Program. The inlets are compared using CFD analysis over a range of wind speeds of 2.5- 15 m/s and sampling flow rate of 1000 liter per minute (lpm). The simulations were performed in 3-dimensional numerical wind tunnel. Two different turbulence models: k-epsilon and detached eddy simulations were used, and the effects of particle – turbulence coupling were examined. The transmission efficiencies for these inlets were evaluated for particles of 10 nm-20um diameter. The modeling results show that for all three inlets transmission decreases with increase of particle size due to particle inertial impaction on the inner walls of the inlets. Additionally, the transmission efficiency decreases at higher wind speeds due to the formation of the strong recirculation zone inside the inlet geometry. DRI Storm Peak and Jungfraujoch inlet efficiencies were found similar for over the range of wind speed and particle sizes. The NOAA inlet was found to have the highest sampling efficiency but was the most sensitive to wind speed, due to its high internal volume. The choice of turbulent dispersion model significantly influences modeling results, especially for high internal volume of the NOAA inlet.

Flow field is solved in a numerical wind tunnel for external flow (Eulerian system)Transient Detached Numerical Simulation (DES) realizable k-e wall treatment Second order numerical convergence scheme

Wind speed varied - Inlet sampling rate is constant – 1000 lpm

Simulations Flow field: Velocity

2.5 m/s wind

15 m/s wind

Particle trajectoriesEfficiency calculation includes gravitational, inertial, turbulent dispersion losses:

ηinlet = # particles transmitted / # massless particles transmitted

Particles are introduced upstream of the inlet (Lagrangian tracking)No bounce boundary condition (particle stick if hit the wall)Turbulent dispersion – Discrete Random Walk (DRW) with random eddy life time

DRW Model validation (external flow)

Lowest penetration of larger particlesFlow is well-structured

DRI inlet Particle Tracks

3D vortex formation at the higher wind speedsSampling on the symmetry plane

NOAA inlet Particle Tracks

Low penetration of larger particlesLow turbulent dispersion losses

NOTE: Simulations were done with a sample flowrate that was 5-6 times greater than in normal operation

Jungfraujoch inlet Particle Tracks

10 m/s wind

Blue - 1 umLight blue–10 um

Red -20 um

Blue - 1 umLight blue–10 um

Red -20 um

Inlet comparison

The transmission efficiencies decrease with increasing particle size Sensitivity to wind speed due to formation of large eddies at higher wind speeds

Blue - 1 umLight blue–10 um

Red -20 um

10 m/s wind

10 m/s wind

New Design of SPL Inlet

m/s

Slotted entrance to re-direct the flow upwardsInternal vanes to limit eddy formation