Cem O. Asma

Preliminary internetworking simulation of the QB50 cubesat constellation

Constellations of small satellites now become a great alternative for scientific missions to study Earth. As a result, they should be considered appropriate communication mechanisms to retrieve the data collected. This article studies the possibility to implement TCP and UDP over IP through the use of intersatellite links and distributed ground stations, such as Genso project. We evaluate parameters like delay end-to-end and throughput for different configurations of the QB50 constellation proposed by von Karman Institute for Fluids Dynamics (VKI).

Comparative Heat Flux Measurements on Standard Models in Plasma Facilities

A comparative experimental study has been performed testing heat flux probes in different European long duration high enthalpy arc heated and inductively heated facilities. Commercial available heat flux sensors, calorimetric probes and SiC probes were used. Tests were carried on three well defined model geometries in stagnation point configuration at two different test conditions defined in terms of specific enthalpy and Pitot pressure. It has been noticed that the reliability of the sensor calibration data is still a major issue. The comparison of measured heat fluxes showed a clear impact of the flow regime (subsonic or supersonic) and enthalpy distribution across the model surface on the results.

Ablative Material Testing at VKI Plasmatron Facility

Ablative material design and improvement need suitable ground testing under high enthalpy flow conditions using intrusive and non-intrusive measurement techniques. The main objective is to develop the ground testing environment adapted for the study of ablative materials at high heat flux levels and provide a database on precise information about the materials to be tested. This paper presents the studies aimed at the testing of graphite and cork ablative material samples at the Plasmatron Facility of the Von Karman Institute, under heat flux levels of around 5-7 MW/m 2

Experimental Investigation of Liquid Fragmentation In Hypersonic Crossflow

This thesis presents an experimental investigation carried out to study penetration and fragmentation of liquid injected into Mach 6 hypersonic cross flow. Flow topology, shock and vortex systems, fragmentation and atomization mechanisms are investigated using high-speed photography, Schlieren photography, flow visualization and Phase Doppler Interferometry techniques. All experiments are conducted at the H-3 Mach 6 wind tunnel facility of the von Karman Institute. Water is used for all tests. Freestream conditions of air flow are kept constant. The variation of the injector geometry and the effect of momentum flux ratio are studied throughout the experimental campaign. Droplet size measurements are analyzed and treated to characterize the atomization process of the liquid jet. The Sauter Mean Diameter and the standard deviation of the droplet size distribution are calculated and presented as a function of location and momentum flux ratio. The obtained Sauter Mean Diameter distribution is compared with the theory available in the literature for lower cross flow speed cases. The whipping phenomenon observed for the low momentum flux ratio liquid injections is explained by frequency maps, which allow one to see the flow domains with similar frequency content. This analysis proposes that the penetration of liquid jet determines the shape of the bow shock, which determines the location and angle of the separation shock. The separation shock is observed to penetrate into liquid phase, playing an important role in fragmentation of liquid, thus changing the penetration height and the shape of the bow shock. A continuous interaction between the liquid penetration, bow shock, separation shock and liquid fragmentation is believed to be the mechanism responsible of the whipping phenomenon. The fragmentation of liquid exposed to Mach 6 air flow is also investigated. Experiments are conducted using water-filled balloons mounted on sharp and blunt leading edge supports. The water-filled balloons are exposed to Mach 6 air flow and high speed camera measurements are taken during the bursting of the balloon, to study the fragmentation of water. Shock patterns and flow topology are visualized by Schlieren photography.

Footprint Analysis of the EXPERT Vehicle Winglet at Hypersonic Conditions

This paper is dedicated to the aerothermodynamic characterization o f the footprint of the Ultra High Temperature Ceramic winglet payload that will be embarked on the ESA reentry demonstrator, EXPERT (Payload 15). Experiments are carried out in the H-3 Mach 6 wind tunnel facility of the von Karman Institute using scaled d own winglet models on a flat plate for the purpose of identifying the aerodynamic and thermal footprint of the winglet on the flat plate. Infrared thermography and sublimation visualization techniques are used to study the thermal footprint; whereas oil fl ow visualization and schlieren techniques are utilized to study the aerodynamic footprint. The position of the winglet and the flow Reynolds number are varied to study the effect of the winglet height to boundary layer thickness ratio. The main flow topology parameters are examined as a function of the winglet height to boundary thickness ratio. The critical regions in terms of increased heat flux and increased aerodynamic shear stress are identified.