the aerodynamics of smoke particle sampling

The aerodynamics of smoke The aerodynamics of smoke particle samplingparticle sampling

Jonas Hedin,Jonas Hedin,Jörg Gumbel,Jörg Gumbel,Markus RappMarkus Rapp

Department of Meteorology Department of Meteorology Stockholm UniversityStockholm University

Outline

• Introduction• Modelling

– Gas flow, particles• Detector designs

– ECOMA, MAGIC• Summary/Outlook

Introduction

Supersonic speeds• Compression &

rarefaction• Composition changes• Chemical reactions• Payload glow• Flow-dependent

sampling efficiencies• Doppler influence• Outgassing...

Introduction

Different flow regimes

• From continuum to free molecular flow via the transition regime

• Knudsen number, Kn=λ/L

Gas flow modelling

Direct Simulation Monte Carlo model (DSMC, G. A. Bird)

• Two-dimensional and axially symmetric

• From continuum to free molecular flow

Gas flow modelling

• The DSMC model analyses the behaviour of individual gas molecules

• Basic inputs are the properties of the undisturbed gas flow and the relevant properties of the payload

• Macroscopic flow properties like density, temperature and velocity fields are obtained

Particle flow modelling• Nanometer-sized

particles tend to follow the airflow around payload structures

• Aerodynamic considerations are of critical importance since we want the particles to hit the detector

ECOMADetection surface, 0 V

-6.2 V +6.2 V

ECOMA

ECOMA

ECOMA

ECOMA

ECOMA

MAGIC

Sampling surface

Summary

• We can model the gas flow and particle flow (neutral and charged) for different detector designs

• Aerodynamical considerations are of critical importance in the design of rocket-borne instruments for in-situ measurements in the MLT region

• Threshold sizes for the detection of meteoric smoke particles have been modelled

Outlook

• Brownian motion• Statistical motion of the particles, outgassing and

desorption• Electric and magnetic fields• 3D simulation

• Asymmetric payloads, different angles of attack• Many open questions

• E.g. what happens when the particle hits the detector surface?