A Computational Analysis of Hypersonic Store Separations

Many current hypersonic vehicles involve shrouds, fairings, boosters, or ejectable payloads separating during flight. It is imperative that they do not strike each other after separation as this typically results in damage or loss of vehicle. This requires a detailed understanding of the flow features involved such as shock waves, expansion waves, shock reflections, and shock wave boundary layer interactions influencing the vehicles\u27 attitude and trajectory. Experimental and flight tests of these scenarios are costly and need massive infrastructure which require difficult measurement techniques to characterize the flow field. Alternatively, numerical simulations can provide accurate, low-cost, and efficient predictions of hypersonic separations. This study looks at the scenarios of a smaller vehicle or store in the flow field of a larger vehicle. Computational fluid dynamics simulations are performed on a $7^\circ$ cone crossing an oblique shock wave at Mach 7 using NASA\u27s OVERFLOW 2.3e Reynolds-averaged Navier Stokes solver. Trajectory and attitude is tracked along with capturing flow features and their imposed forces. The vehicle\u27s dynamics when passing through a shock appears to predominantly the result of differential flow incidence angles causing a strong shock leading to a large pressure increase over a fraction of the vehicle which influences pitch. The vehicle appears to follow conventional longitudinal stability theory and becomes more stable during the interaction with the center of pressure moving aft and the peak pitching moment happening when the shock passes through the center of gravity if allowed to continue through the body. Complex shock wave boundary layer interactions are seen which could complicate specific separation scenarios. Nonphysical anomalies are seen in the flow field which are theorized to be the result of OVERFLOW\u27s implicit solution algorithm but are shown to have little influence on results. Likewise, the applied forces and moments along with center of pressure in this scenario are shown to be unaltered by hybrid Reynolds-averaged Navier-Stokes and Large eddy simulations in the form of delayed detached eddy simulation

Gilbert-Taylor cones and multi-phase Electrospinning

In this thesis a numerical method is developed, which allows to compute the shape of electrically charged liquid surfaces of droplets of finite conductivity

Abrupt contraction flow of magnetorheological fluids

International audienceContraction and expansion flows of magnetorheological fluids occur in a variety of smart devices. It is important therefore to learn how these flows can be controlled by means of applied magnetic fields. This paper presents a first investigation into the axisymmetric flow of a magnetorheological fluid through an orifice so-called abrupt contraction flow. The effect of an external magnetic field, longitudinal or transverse to the flow, is examined. In experiments, the pressure-flow rate curves were measured, and the excess pressure drop associated with entrance and exit losses was derived from experimental data through the Bagley correction procedure. The effect of the longitudinal magnetic field is manifested through a significant increase in the slope of the pressure-flow rate curves, while no discernible yield stress occurs. This behavior, observed at shear Mason numbers 10Mnshear100, is interpreted in terms of an enhanced extensional response of magnetorheological fluids accompanied by shrinkage of the entrance flow into a conical funnel. At the same range of Mason numbers, the transverse magnetic field appears not to influence the pressure drop. This can be explained by a total destruction of magnetic particle aggregates by large hydrodynamic forces acting on them when they are perpendicular to the flow. To support these findings, we have developed a theoretical model connecting the microstructure of the magnetorheological fluid to its extensional rheological properties and predicting the pressure-flow rate relations through the solution of the flow equations. In the case of the longitudinal magnetic field, our model describes the experimental results reasonably well

Large-eddy simulation of shallow turbulent wakes behind a conical island

Large-Eddy Simulations (LESs) and experiments were employed to study the influence of water depth on the hydrodynamics in the wake of a conical island for emergent, shallow, and deeply submerged conditions. The Reynolds numbers based on the island's base diameter for these conditions range from 6500 to 8125. LES results from the two shallower conditions were validated against experimental measurements from an open channel flume and captured the characteristic flow structures around the cone, including the attached recirculation region, vortex shedding, and separated shear layers. The wake was impacted by the transition from emergent to shallow submerged flow conditions with more subtle changes in time-averaged velocity and instantaneous flow structures when the submergence increases further. Despite differences in the breakdown of the separated shear layers, vortex shedding, and the upward flow region on the leeward face (once the cone's apex is submerged), similar flow structures to cylinder flow were observed. These include an arch vortex tilted in the downstream direction and von Karman vortices in the far-wake. Spectra of velocity time series and the drag coefficient indicated that the vortex shedding was constrained by the overtopping flow layer, and thus the shedding frequency decreased as the cone's apex became submerged. Finally, the generalised flow structures in the wake of a submerged conical body are outlined

NAS (Numerical Aerodynamic Simulation Program) technical summaries, March 1989 - February 1990

Given here are selected scientific results from the Numerical Aerodynamic Simulation (NAS) Program's third year of operation. During this year, the scientific community was given access to a Cray-2 and a Cray Y-MP supercomputer. Topics covered include flow field analysis of fighter wing configurations, large-scale ocean modeling, the Space Shuttle flow field, advanced computational fluid dynamics (CFD) codes for rotary-wing airloads and performance prediction, turbulence modeling of separated flows, airloads and acoustics of rotorcraft, vortex-induced nonlinearities on submarines, and standing oblique detonation waves

Transport and deposition patterns in drying sessile droplets

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106826/1/aic14338.pd