Measurement technique for the determination of the deformation of a flexible thermal protection ring inside solid fuel booster rocket
A new generation of the solid booster rockets of the Ariane 5 launcher is being under construction to improve stability and controlling characteristics of the vehicle. One crucial element of solid rocket boosters is the separator ring that permits the division of the total quantity of solid fuel into well defined, independent stages. Up to now, these separator rings introduced some unwanted perturbations in the operation of the launcher, thus they are replaced by a flexible element, the characteristics of which are to be investigated. The flexible thermal protection ring is able to change its form due to the gas flow inside the booster. The form is changed partially due to deformation induced by the flow, and by erosion effects due to the burning fuel. At the present investigation the flow induced deformation is measured. The measurements were carried out in a facility that does not take into account the effects of burning, thus optical access was possible. An optical image treatment based technique was developed and applied for the determination of the deformation of the thermal protection ring for various flow velocities. The method was found to be accurate, robust and reliable, thus it can be used as a reference measurement technique for the calibration of other type of nonoptical sensors that can be used later also in fuel burning conditions. This technique is discussed in this publication in detail. Keywords—Fluid structure interaction, optical technique, Ariane 5
Cold flow investigation of the flow acoustic coupling in solid propellant boosters
This paper deals with an analysis of the flow instabilities in the Ariane 5 solid propellant booster. They may occur as vortices shed from partiallyburned inhibitors can excite one of the acoustic modes of the cavity, leading to a flow-acoustic coupling. The fundamental aspects of axial flow instabilities promoted by two obstructions in a cylindrical duct ended by a nozzle and their interference with the acoustic field are firstly investigated. Resonant pressure fluctuations occur at several velocities coinciding to the existence of an integer number of vortices between the obstacles, with no more than 4 vortices observed. After this, the flow-acoustic coupling is studied in a setup respecting the geometrical and dynamic similarity with the real booster at a 1/15* scale with radial flow simulation and sonic condition at the nozzle. Vortex shedding is characterized by a constant Strouhal number of 0.6 but its frequency remains too far from the acoustic ones for flow-acoustic coupling to be possible. The use of porous walls for simulating the radial flow affects the acoustic field and the improvement of the side injection technique is under way at VKI. The nature of the flow in the combustion chamber is complex since it generates radially from the burning surface and then develops longitudinally to reach the exhaust nozzle where it interacts with a very complex geometrical shape. The three segments are separated by two inhibitor rings which, during combustion, may protrude into the flow-field giving rise to a possible vortex shedding (figure 2). So, flow instabilities may occur as vortices shed from partially-burned propellant inhibitors can excite one of the acoustic mode of the cavity, leading to a resonant flow acoustic coupling. Excitation of acoustic modes by flow instabilities could result in significant pressure fluctuations in the combustion chamber, with the consequent adverse effect upon stability of the combustion itself and upon rocket performances. This exhibition of pressure and thrust oscillations is already recorded in the literature for rockets of similar dimensions (U.S. Space Shuttle and Titan SRM)''.
General expression for the density effect for the ionization loss of charged particles
The equations for the density-effect correction $\ensuremath{\delta}(X)$ for the ionization loss as given in a previous paper have been extended to the case where $\ensuremath{\delta}({X}_{0})\ensuremath{\equiv}{\ensuremath{\delta}}_{0}g0$. Here ${X}_{0}$ is the lower limit of the range ${X}_{0}lXl{X}_{1}$, where a particularly simple expression for $\ensuremath{\delta}(X)$ applies; $X={log}_{10}(\frac{p}{{m}_{0}c})$, where $p$ is the momentum and ${m}_{0}$ is the mass of the incident particle. The case ${\ensuremath{\delta}}_{0}g0$ applies directly to the calculation of $\ensuremath{\delta}(X)$ for conductors (metals).