Heat flux augmentation caused by surface imperfections in turbulent boundary layers

Aerodynamic heating of hypersonic vehicles is one of the key challenges needed to be overcome in the pursuit of hypersonic ascent, re-entry, or sustained flight. Small, unavoidable imperfections are always present on the surface of aircraft in the form of steps, gaps, and protuberances. These can lead to high levels of localised heat flux augmentation, up to many times the undisturbed level. Flat plate experiments have been carried out in the Oxford High Density Tunnel with the aim of characterising the heating effects caused by small scale protuberances and steps in turbulent boundary layers. The current work presents experimental heat flux augmentation data, an assessment of existing heat flux correlations, and introduces new engineering level correlations to describe heat flux augmentation for a range of surface geometries

Vehicle and mission design of a future small payload launcher

This paper presents the conceptual design and performance analysis of a partially reusable space launch vehicle for small payloads. The system uses a multi-stage vehicle with rocket engines, with a reusable first stage capable of glided or powered flight, and expendable upper stage(s) to inject a 500 kg payload in different low Earth orbits. The space access vehicle is designed to be air-launched from a modified aircraft carrier. The aim of the system design is to develop a commercially viable launch system for near-term operation, thus emphasis is placed on the efficient use of high TRL technologies. The vehicle design are analysed using a multi-disciplinary design optimisation approach to evaluate the performance, operational capabilities and design trade-offs

Robust multi-objective optimisation of a descent guidance strategy for a TSTO spaceplane

This paper presents a novel method for multi-objective optimisation under uncertainty developed to study a range of mission trade-offs, and the impact of uncertainties on the evaluation of launch system mission designs. A memetic multi-objective optimisation algorithm, MODHOC, which combines the Direct Finite Elements transcription method with Multi Agent Collaborative Search, is extended to account for model uncertainties. An Unscented Transformation is used to capture the first two statistical moments of the quantities of interest. A quantification model of the uncertainty was developed for the atmospheric model parameters. An optimisation under uncertainty was run for the design of descent trajectories for the Orbital-500R, a commercial semi-reusable, two-stage launch system under development by Orbital Access Lt

The Inner-Shelf Dynamics Experiment

17 USC 105 interim-entered record; under review.The article of record as published may be found at http://dx.doi.org/10.1175/BAMS-D-19-0281.1The inner shelf, the transition zone between the surfzone and the midshelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from September–October 2017, conducted from the midshelf, through the inner shelf, and into the surfzone near Point Sal, California. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves, and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the midshelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean.U.S. Office of Naval Research (ONR)ONR Departmental Research Initiative (DRI)Inner-Shelf Dynamics Experiment (ISDE

Computation of the TACOT Intercalibration Testcase for the 4th AFOSR/SNL/NASA Ablation Workshop using FABL

The TACOT testcase will be computed using FGE\u27s ablation code FABL. Results will be presented for the purposes of inter-model comparison and calibration. FABL is a \u27standard\u27 effective properties code with the following modules: Basic numerical method : STAB2 (1D implicit shrinking grid with multi-materials , contact resistances etc) Multiple Arrhenius decomposition from TGA, with arbitrary grouping (resin/fibres/contaminants) Equilibrium or non-equilibrium pyrolysis gas treatment Internal pressures from Darcy type law Iterative TPS sizing for input design rules. Adjoint scheme and simple optimiser for fitting of effective properties to arc heater or flight measurements (or sets of) Simple surface chemistry modules for surface energy balance: Carbon ablation (kinetic, diffusion limit, sublimation) Teflon model Melt failure (silica etc) Variable surface stoichiometry materials + failure Surface roughness evolution model based on differential ablation rates, shape factor and Dirling correlation. (used when coupling to flow codes) Flame front model with equilibrium/frozen burn treatment for pyrolysis gases for charring ablators. The burn efficiency is an empirical factor. Boundary conditions can be defined in terms of temperature or heat flux

Measurements of heat transfer on hemispheres at rarefied flow conditions using liquid crystals

In the study of space debris re-entry heating, there are to this day significant uncertainties in the distribution of thermal fluxes incident upon re-entering spacecraft and debris. In order to improve the accuracy of such calculations, experiments have been conducted in the recently refurbished Oxford Low Density Tunnel (LDT) to characterise the heat transfer distribution over a pair of hemisphere-capped cylinders measuring 10mm and 15mm in diameter. These models were constructed of Perspex, and were designed as simple geometric analogues of satellite components such as those utilised by current debris simulation codes. Two separate freestream conditions were achieved during tests, with corresponding Mach numbers of 5.4 and 5.8, and Knudsen number of 0.02 and 0.1, respectively. The hemisphere-capped cylinders were coated with a slurry of thermochromic liquid crystals and were oriented with their long axes parallel to the freestream flow direction in the LDT. Upon initialisation of the plume from the facility's contoured nozzle, visual changes in the thermochromic coating were induced due to heat transfer from the incident hypersonic flow. This "colour play" was then recorded, and the resulting video analysed using an in-house post-processing code, thus calculating the surface distributions of heat transfer coefficient on each model. Finally, the operational characteristics of the LDT and details of its recent upgrades are briefly described. A characterisation of the facility's flow capabilities is then presented in terms of Pitot pressure and total temperature measurements of the experimental plume

Experimental investigation of the effect of steps and gaps on hypersonic vehicles

The design of hypersonic vehicles typically incorporates the use of simple, geometric shapes with smooth surfaces. There are many reasons why aircraft cannot have perfectly smooth surfaces with small, unavoidable imperfections frequently being present. These can appear in many forms, such as gaps between tiles and rivets joining different panels. Surface features like this are mainly detrimental to aircraft performance for two reasons: they can cause premature boundary layer transition, leading to higher integrated heat loads and unexpected aerodynamic loads; and they cause highly localised areas of heat flux augmentation – up to many times the undisturbed level. This work is part of a project which aims to characterise some of these effects using a combination of experimental and numerical techniques with the overall aim being to produce useful engineering level correlations for use in vehicle design. This paper presents initial experiments performed in the Oxford High Density Tunnel (HDT). Heat flux and pressure data have been acquired for a range of step and cavity geometries, and capability of a sophisticated experimental model has been shown