J. Stevens
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2 records found
1
Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique
A test case of the Mars Express Phobos fly-by
Context. The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet-satellite systems. Aims. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 μm/s at a 10 s integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to ∼50 m.
aiming at the comparison between different state-of-the-art numerical models for the simulation of
wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereoscopic
Particle Image Velocimetry was employed to obtain the velocity field and turbulence statistics in the near
wake of a two-bladed wind turbine model and of a porous disc, which mimics the numerical actuator
used in the simulations. Researchers have been invited to simulate the experimental case based on the
disc drag coefficient and the inflow characteristics. Four large eddy simulation (LES) codes from different
institutions and a vortex model are part of the comparison. The purpose of this benchmark is to validate
the numerical predictions of the flow field statistics in the near wake of an actuator disc, a case that is
highly relevant for full wind farm applications. The comparison has shown that, despite its extreme
simplicity, the vortex model is capable of reproducing the wake expansion and the centreline velocity
with very high accuracy. Also all tested LES models are able to predict the velocity deficit in the very near
wake well, contrary to what was expected from previous literature. However, the resolved velocity
fluctuations in the LES are below the experimentally measured values. ...
aiming at the comparison between different state-of-the-art numerical models for the simulation of
wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereoscopic
Particle Image Velocimetry was employed to obtain the velocity field and turbulence statistics in the near
wake of a two-bladed wind turbine model and of a porous disc, which mimics the numerical actuator
used in the simulations. Researchers have been invited to simulate the experimental case based on the
disc drag coefficient and the inflow characteristics. Four large eddy simulation (LES) codes from different
institutions and a vortex model are part of the comparison. The purpose of this benchmark is to validate
the numerical predictions of the flow field statistics in the near wake of an actuator disc, a case that is
highly relevant for full wind farm applications. The comparison has shown that, despite its extreme
simplicity, the vortex model is capable of reproducing the wake expansion and the centreline velocity
with very high accuracy. Also all tested LES models are able to predict the velocity deficit in the very near
wake well, contrary to what was expected from previous literature. However, the resolved velocity
fluctuations in the LES are below the experimentally measured values.