The aerodynamics of smoke particle sampling

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

10. ECOMA

11. ECOMA

12. ECOMA

13. 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?