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?