1. The aerodynamics of smoke particle sampling Jonas Hedin, Jörg Gumbel, Markus Rapp Department of Meteorology Stockholm University

2. Outline Introduction Modelling –Gas flow, particles Detector designs –ECOMA, MAGIC Summary/Outlook

3. Introduction Supersonic speeds Compression & rarefaction Composition changes Chemical reactions Payload glow Flow-dependent sampling efficiencies Doppler influence Outgassing...

4. Introduction Different flow regimes From continuum to free molecular flow via the transition regime Knudsen number, Kn=λ/L

5. Gas flow modelling Direct Simulation Monte Carlo model (DSMC, G. A. Bird) Two-dimensional and axially symmetric From continuum to free molecular flow

6. 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

7. 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

8. ECOMA Detection surface, 0 V -6.2 V+6.2 V

9. ECOMA

14. MAGIC Sampling surface

15. 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

16. 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?