The aim is to develop an impaction-based particle collector that enables aerosol impacts in the free supersonic flow radially next to the rocket body (for details on the rocket, see [2]). Numerical simulations with the PDE software COMSOL Multiphysics support the development of the collector design. Of particular interest is the evaluation of the evolving flow field around the payload of a sounding rocket at high Mach numbers (with Ma₁ = 1.31 and Ma₂ = 1.75 in 85 km) including the main flow variables (e.g. velocity, pressure). Furthermore, the thickness of the boundary layer is examined in order to prevent it from influencing the impaction processes as an artifact. Further questions are aimed at the design and arrangement of the impactor arms. Finally, particle trajectories are calculated on the basis of the ambient conditions, which lead to the confirmation of possible impact processes.

The simulations consider three different flight attitudes (i.e. angles of attack) of the sounding rocket during flight: 0° and ±30° (angle between the direction of attack and the longitudinal axis of the rocket). The simulations are carried out for flight speeds of 300 m/s and 400 m/s. The resulting flow fields show corresponding shock waves generated both at the payload tip and at the protrusions. Figure 1 shows the evaluated flow field quantities at the incident flow velocity of 400 m/s of the final scientific payload geometry with measurement surfaces. Temperature, air density and velocity for an angle of attack of -30° are shown in a sectional plane. The asymmetrical shock wave region that arises at this point, in which steep gradients occur, is visible. In addition, the thickness of the boundary layers at each of the calculated rocket positions is evaluated. Based on this, the distance of the impactor arms from the payload envelope is determined in order to sample particles in the free flow. The cloud ice particles of NLCs presumably exist under comparatively unstable conditions at mesospheric altitudes. Temperature fluctuations, as they occur in the flow field around the rocket body, probably cause the ice to sublimate. Therefore, the particle trajectories are calculated for very small ice cores (with a diameter of 1.2 nm), which are released after complete sublimation of the former ice particle. Since the concentration of NLC cloud particles is estimated to be around 10 1/cm³ [3], simulations are carried out with a wide range of particle concentrations (1 to 38 1/cm³). The results of the particle simulations show impact processes (see Figure 1) on the impactor surfaces, which provides strong evidence that the impact mechanism will also occur in reality.

The numerical simulations allow the flow field around the payload of a sounding rocket to be analyzed, including the corresponding flow variables and the developing boundary layer. These analyses are used to design a measurement device for particle impaction and the probability of particle impact on the designated collection surfaces is highly estimated based on the calculated particle trajectories.

REFERENCES

[1] M. Süßen. Sikimedia commons. commons.wikimedia.org/w/index.php= Special:MediaSearch&go=Go&type=image, 2019. Accessed: 2021-06-02.

[2] K. Naumann, C. Kirchberger, O. Drescher, D. Hargarten, M. Zurkaulen, A. Haubl, S. Rest, H. Niedermaier, J. Ramsel. Design of a hovering sounding rocket stage for measurements in the high atmosphere, 2020.

[3] R. P. Turco, O. B. Toon, R. C. Whitten, R. G. Keesee, D. Hollenbach. Noctilucent clouds: Simulation studies of their genesis, properties and global influences, Planetary and Space Science, 1982.

Project partner

• Johannes Gutenberg University Mainz
• DLR MORABA Oberpfaffenhofen
• Max Planck Institute for Chemistry Mainz