Enhancing the test time performance of Ludwieg tunnels

Ground testing at hypersonic conditions requires either expensive heating or reduced test time. This paper discusses further developments to a mode of operation for Ludwieg Tunnels - Plenum Augmented Ludwieg Mode (PALM) - in the Oxford High Density Tunnel (HDT). PALM offers increased test time performance relative to standard Ludwieg Mode at the expense of total pressure and unit Reynolds number capability. A description of the theory of operation and the implementation of PALM in the HDT is given. Experimental results, quasi-1D numerical simulations and a performance map are presented. PALM has been demonstrated to offer a factor of 10 increase in the test time with a reduction in maximum Unit Reynolds number of approximately 50% relative to standard Ludwieg Mode. Theoretical performance maps predict that PALM can offer a factor of 10 improvement in test time for all Mach 7 unit Reynolds numbers run to date in HDT without any facility upgrades. Hence, operation in PALM significantly improves the capability of the HDT to investigate unsteady and long duration flow phenomena relative to standard Ludwieg Mode operation

Extension of test time in Ludwieg tunnels

Two new, longer duration, modes of operation for Ludwieg Tunnels have been implemented in the Oxford High Density Tunnel (HDT): Extended Ludwieg Mode (ELM) and Plenum Augmented Ludwieg Mode (PALM). In standard Ludwieg Tunnel operation, the duration of the steady test time is limited by the return of the rarefaction wave to the facility nozzle throat. Operation in ELM extends the rarefaction wave such that the tail is generated as the head returns and results in a steady decrease in supply pressure. PALM takes advantage of the dual-throat arrangement of the HDT, which features a plenum region between the facility barrel and the nozzle throat, and tailors plug valve opening to produce a steady supply pressure to the facility nozzle at the expense of total pressure capability. This paper describes the theory of operation of these new modes, their implementation in the existing Oxford High Density Tunnel and presents transient quasi-1D numerical simulations confirming their principles of operation. It then presents experimental results from initial testing of the HDT in the new modes. These results demonstrate a successful implementation of ELM, producing a test flow that is over fifteen times longer, but of comparable steadiness to a Mach 7 Ludwieg Mode plateau in the Oxford HDT. PALM was implemented with partial success, resulting in a test flow that is both ten times the duration of, and significantly steadier (for supply pressure and unit Reynolds number), than a Ludwieg Mode plateau. Thus, the implementation of ELM and PALM significantly expand the capability of the facility to investigate long duration flow phenomena

Thermal effects of plume impingement on a hypersonic vehicle

The thermal effects of plume impingement on the uselage of a hypersonic vehicle were investigated using a plume generator mounted to a flat plate model in the Oxford High Density Tunnel at Mach 7. The model was instrumented with thin film heat transfer gauges, pressure transducers, Pressure Sensitive Paint and thermocouples. Schlieren photography was used to visualize the flowfield. Exit Pressure Ratios of up to 22 were tested, with CO2 as the cold injected gas. Three nozzles were used to explore the effect of changing the expansion profile on heat transfer: a 5 mm conical nozzle, a 6 mm conical nozzle and a 6 mm Rao nozzle. It has shown that initially Stanton number decreases by up to 90% with cold gas injection, but flow separation causes the Stanton number to increase up to 125% of the no injection condition. This significant decrease in heat transfer indicates that there will be direct contact between the rocket engine plume and the fuselage, allowing for significant heat transfer to the fuselage

Iron and infection: effects of host iron status and the iron-regulatory genes haptoglobin and NRAMP1 (SLC11A1) on host-pathogen interactions in tuberculosis and HIV.

There are many lines of evidence illustrating that iron plays a pivotal role in modulating the battle for survival between mammalian hosts and their pathogens. Each displays considerable genetic investment in a wide range of mechanisms for acquiring and maintaining iron. These competitive mechanisms are highly complex, existing within an interacting matrix of absorption, transport, storage and detoxification systems, each of which are iron-responsive and thus able to adapt to the different phases of infection. Considerable genetic polymorphism in some of these systems, with signals of geographic selection in the hosts, and niche selection in the pathogens, indicates that they are critical for species survival. In this review we briefly summarize the role of iron in host immune function before reviewing the available evidence that iron modulates susceptibility and disease outcomes in HIV and TB (tuberculosis). We then examine the putative role of iron-related host genes by focussing on two candidate genes, haptoglobin and NRAMP1, for which there are common polymorphic variants in humans with strong evidence of functionally distinct biochemical phenotypes that would be predicted to influence the course of HIV and TB infections. Finally, we examine the limited evidence so far available that nutrient-gene interactions are likely to influence the way in which gene variants can protect against infection. We conclude that there is a wealth of evidence associating alterations in iron balance and in iron-regulatory systems with disease progression, but that many issues related to the direction of causality, mechanisms of action and sensitivity to pharmacological intervention remain to be elucidated. Since iron is probably the most widely prescribed compound throughout the world, used in both preventative and treatment regimens, a deeper understanding of the host-pathogen interactions relating to iron constitutes an important area for both basic and clinical research