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?/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?