A High Elevation Aerosol Inlet Modeling Study and Inter-comparison

1. A High Elevation Aerosol Inlet Modeling Study and Inter-comparison A. Gannet Hallar1, Ian McCubbin1,Igor Novosselov2, Riley Gorder2, John Ogren3 1:DRI – Storm Peak Laboratory 2:Enertechnix, Inc. 3:NOAA-ESRL-GMDL Inlet comparison DRW Model validation (external flow) • 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. Factors in Sampling Efficiency DRI inlet Particle Tracks The transmission efficiencies decrease with increasing particle size Sensitivity to wind speed due to formation of large eddies at higher wind speeds ηsampling =ηaspiration *ηtransmission Lowest penetration of larger particles Flow is well-structured New Design of SPL Inlet 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 Slotted entrance to re-direct the flow upwards Internal vanes to limit eddy formation Computational Domain Blue - 1 um Light blue–10 um Red -20 um 10 m/s wind NOAA inlet Particle Tracks Numerical wind tunnel : inlet 1m x 1m Total in wind tunnel ~ 5,000,000 cells Wind speeds: 2.5 -15 m/s Particle sizes: 10nm – 20micron 3D vortex formation at the higher wind speeds Sampling on the symmetry plane Modeling of Current Inlets - 1000 lpm Effects of Wind Speed and Particle Size. Blue - 1 um Light blue–10 um Red -20 um DRI - Storm Peak Laboratory, CO NOAA, DOE ARM networks multiple locations Jungfraujoch Typical sampling rate 200 lpm Simulations Flow field: Velocity 2.5 m/s wind 10 m/s wind Jungfraujochinlet Particle Tracks Low penetration of larger particles Low turbulent dispersion losses NOTE: Simulations were done with a sample flowrate that was 5-6 times greater than in normal operation 15 m/s wind 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 Blue - 1 um Light blue–10 um Red -20 um Particle trajectories Jungfraujoch NOAA • Efficiency 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 DRI - SPL 10 m/s wind m/s