Inhaltszusammenfassung

This investigation applies computational fluid dynamics simulations to support the design development of an impaction-based particle collector. This collector aims at submicron aerosol sampling in the supersonic free stream radially aside a sounding rocket body in the mesosphere (altitude of 85 km). The overall goal of the development process is to collect mesospheric aerosols for their physico-chemical analyses to gain further insights into high atmosphere processes: e.g. of aerosol part...This investigation applies computational fluid dynamics simulations to support the design development of an impaction-based particle collector. This collector aims at submicron aerosol sampling in the supersonic free stream radially aside a sounding rocket body in the mesosphere (altitude of 85 km). The overall goal of the development process is to collect mesospheric aerosols for their physico-chemical analyses to gain further insights into high atmosphere processes: e.g. of aerosol particles from meteoric ablation and their potential impact on noctilucent cloud (NLC) formation. However, sampling of particles at these heights and their analyses is only possible by considerable costs and great effort by using sounding rockets, which is why only a sparse database is available so far. The development process and efficiency analyses are based on numerical simulations achieved by the software COMSOL Multiphysics®, where the simulation workflow is divided into two independent studies: First, with the CAD Import Module in COMSOL®, the detailed rocket geometry (as far as relevant for the particle collection efficiency) is implemented into the model. Then, the supersonic flow field surrounding the rocket under varying flight attitudes is simulated by the High Mach Number Laminar Flow Interface in COMSOL Multiphysics® by solving the Navier-Stokes equations for compressible fluids, whereby a steady state solution is obtained. Of particular interest for the design and arrangement of the probe collector is (a) the evaluation of the evolving flow field around the sounding rocket at the free stream Mach number of Ma = 1.75 (at 85 km height) and (b) the localization as well as the impact of the occurring shockwave on the particle sampling. Furthermore, the thickness of the boundary layer around the rocket body is investigated to ensure a particle sampling well away of perturbing influences. Additionally, for modeling the particle trajectories and thus the aerosol impactions on the probe collector, Particle Tracing for Fluid Flow in COMSOL® is utilized, where Newton’s second law is applied. For this purpose, a preliminary investigation of possible particle forces and their magnitude is performed and corresponding forces (drag and Brownian force) are considered in the model. With the final collector design, the number of impacted particles (by particle counter application in COMSOL Multiphysics®) on collector surfaces are analyzed in a parameter study (Parametric Sweep) for aerosol sizes of 1.2 nm diameter at various number concentrations. Therefrom, the potential sampling efficiency of the probe collector is estimated. In conclusion, impactions onto designated collector surfaces are highly probable according to simulation results. Moreover, our COMSOL® model can be validated by measurement results of the future planned rocket flight» weiterlesen» einklappen

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DDC Sachgruppe:
Mathematik