Melrose Brown

Investigation of a Compression Corner at Hypersonic Conditions using a Reynolds Stress Model

An experimental campaign over a compression corner in a Mach 6 hypersonic flow was conducted to investigate the performance of a differential Reynolds stress model (RSM). Two compression angles have been chosen in order to obtain an attached flow (15-degrees) and a separated flow (40-degrees). The numerical results obtained using the RSM were compared with the numerical findings and with the results from standard linear eddy viscosity models and an explicit algebraic Reynolds stress model. As expected, all models performed similarly for the 15-degrees case in terms of wall pressure and heat flux while appreciable differences were visible at 40-degrees when the boundary layer separates. In this case the Reynlds stress based models proved to be superior to the eddy viscosity ones.

Sensitivity Analysis towards Probabilistic Re-Entry Modeling of Spacecraft and Space Debris

We present work towards the development of a new tool, FOSTRAD (Free Open Source Tool for Re-entry of Asteroids and Debris) that will use a combination of the spacecraftand object-oriented approaches and will incorporate uncertainty quantification. The current work presents progress towards incorporating uncertainty quantification by performing aeroand aerothermo-dynamic sensitivity analyses for a sphere, cube, and a cylinder with respect to the uncertain atmospheric and object parameters. The sensitivity analysis is performed using high fidelity tools such as the Direct Simulation Monte Carlo (DSMC) and the Computational Fluid Dynamics (CFD) methods. In FOSTRAD, aerodynamic computations in the continuum and free molecular regimes are performed using Modified Newtonian Theory and the free molecular analytical models of Schaaf and Chambre, respectively. For the rarefied transition regime, recently developed sigmoid bridging function is used for better tracking of the data. Analytical aerothermodynamic relations for strong shocks exist only for blunt objects that have a finite radius of curvature at the nose (like a sphere), but not for sharp-edged objects such as the cube and cylinder. We use the results from the sensitivity analyses to develop mathematical relations for the variation of aerothermodynamic properties for cube and cylinder. We also develop mathematical relations for the heat flux distribution on the surface of these objects.

Scaling of plasma-body interactions in low Earth orbit

This paper derives the generalised set of dimensionless parameters that scale the interaction of an unmagnetised multi-species plasma with an arbitrarily charged object - the application in this work being to the interaction of the ionosphere with Low Earth Orbiting (LEO) objects. We find that a plasma with K ion species can be described by 1 + 4 K independent dimensionless parameters. These parameters govern the deflection and coupling of ion species k, the relative electrical shielding of the body, electron energy, and scaling of temporal effects. The general shielding length λ ϕ is introduced, which reduces to the Debye length in the high-temperature (weakly coupled) limit. The ability of the scaling parameters to predict the self-similar transformations of single and multi-species plasma interactions is demonstrated numerically using pdFOAM, an electrostatic Particle-in-Cell—Direct Simulation Monte Carlo code. The presented scaling relationships represent a significant generalisation of past work, lin...

Charged aerodynamics of a Low Earth Orbit cylinder

This work investigates the charged aerodynamic interaction of a Low Earth Orbiting (LEO) cylinder with the ionosphere. The ratio of charge to neutral drag force on a 2D LEO cylinder with diffusely reflecting cool walls is derived analytically and compared against self-consistent electrostatic Particle-in-Cell (PIC) simulations. Analytical calculations predict that neglecting charged drag in an O+ dominated LEO plasma with a neutral to ion number density ratio of 102 will cause a 10% over-prediction of O density based on body accelerations when body potential (ɸB) is ≤ −390 V. Above 900 km altitude in LEO, where H+ becomes the dominant ion species, analytical predictions suggest charge drag becomes equivalent to neutral drag for ɸB ≤ −0.75 V. Comparing analytical predictions against PIC simulations in the range of 0 < − ɸB < 50 V found that analytical charged drag was under-estimated for all body potentials; the degree of under-estimation increasing with ɸB. Based on the −50 V PIC simulations, our in-house...

A Kalman-Filter Based Inertial Navigation System Processor for the SCRAMSPACE 1 Hypersonic Flight Experiment

The design of a navigation processor for the SCRAMSPACE 1 hypersonic flight experiment is detailed. Two cascaded extended Kalman filters provide a fusion of gyroscope, accelerometer, magnetometer, GPS and aerodynamic database sources for vehicle state estimation. Two quantities of great interest for SCRAMSPACE 1 are angle of attack and side-slip angle. The navigation processor performs estimations in two stages. The first stage tracks the vehicles navigation states with a commercial grade Inertial Measurement Unit (IMU)/GPS combination, starting at the conclusion of a despin manoeuvre. It is initialised by a navigation- grade Inertial Navigation System (INS). A 25-run Monte Carlo sweep shows that without a navigation filter, the first stage cannot hold attitude via raw gyroscope integration over the 468 seconds necessary. The filtered estimate has a 72% chance of holding attitude over this time, with 5.5, 6.3 and 14.9 degrees of standard deviation of roll pitch and yaw error. A prototype proof-ofconcept attitude determination system is shown to confirm the performance in reduction of attitude drift, compared with that of integrating the gyroscope measurements directly. In a stationary test over 240 seconds, the integrated gyroscope solution drifts 160 degrees in roll, 12 degrees in pitch and 47 degrees in yaw. The magnetometer-integrated solution drifts 5 degrees in roll, 1 degree in pitch and 10 degrees in yaw. In a dynamic test over 64 seconds, in which pure rotations are induced, the integrated gyroscope solution drifts 40 degrees in roll, 10 degrees in pitch and 20 degrees in yaw. The second stage of the experiment utilises known vehicle dynamics to estimate angle of attack and sideslip on re-entry to the atmosphere. The estimations are shown to be within 0.1 degrees of the truth, even when the INS-computed relative wind angles are an order of magnitude out and the wrong sign.