The design of a transpiration cooled system requires detailed local heat transfer information on and in the vicinity of the porous injector; however, limited spatially resolved experimental studies exist, particularly in hypersonic flows. In this work experiments were conducted in the Oxford High Density Tunnel at Mach 6.1 in both laminar and turbulent regimes. Spatially resolved 2D surface heat transfer measurements were acquired by imaging directly on and downstream of two micro-porous transpiration cooled injectors (METAPOR CE170 and Zirconia) using high-speed infra-thermography. Whilst injection in the laminar regime results in a steady, monotonic reduction in heat transfer from the start of the injector, a flatter profile is present for the turbulent cases where turbulent mixing inhibits surface heat transfer reduction.

This paper presents a novelexperimental technique where infra-red thermography is employed to directly measure the surface heat transfer of a transpiration cooled porous material in transient hypersonic flow. Experiments were conducted in the Oxford High Density Tunnel on a flat faced hemispherical probe at a single Mach 7 free-stream condition (𝑅𝑒 𝑢 = 3.84•10 6 1/m) with Nitrogen, Air, Argon, Krypton and Helium injection gases and mass flow rates ranging from 0.01-0.235 kg s −1 m −2 . Surface heat transfer measurements were extracted by imaging directly on the porous material using a FLIR A6751 high-speed long-wave infra-red camera. Porous alumina was chosen due to its favourable thermal properties for infra-red analysis and its very small pore sizes (≈ 2 𝜇m) enabling a uniform outflow. It was found that the Stanton number reduction matched to within 10% of both CFD results and correlations. Nomenclature 𝐵 ℎ Blowing parameter 𝑐 𝑝 Specific heat capacity, J kg −1 K −1 CFD Computational fluid dynamics 𝐼 Radiant intensity, W m −2 sr −1 GIS Gas injection system 𝐻 Enthalpy, J ℎ Planck's constant, m 2 kg s −1

Accurate assessment of nozzle guide vane (NGV) capacity is essential for understanding engine performance data, and to achieve accurate turbine stage matching. In accelerated engine development programmes in particular, accurate and early assessment of NGV capacity is a significant advantage. Whilst the capabilities of computational methods have improved rapidly in recent years, the accuracy of absolute capacity prediction capability is lower than experimental techniques by some margin. Thus, experimental measurement of NGV capacity is still regarded as an essential part of many engine programmes. The semi-transient capacity measurement technique, developed and refined at the University of Oxford over the last 10 years, allows rapid and accurate measurement of engine component (typically fully cooled NGVs) capacity at engine-representative conditions of Mach and Reynolds numbers and coolant-to-mainstream pressure ratio. The technique has been demonstrated to offer considerable advantages over traditional (industrial steady-state) techniques in terms of accuracy, time and operating cost. Since the original facility was constructed, the facility has been modularised to allow for rapid interchange of test vane modules, and the instrumentation has been optimised to drive down the uncertainty in NGV capacity. In this paper, these improvements are described in detail, and a detailed uncertainty analysis is presented of the original facility, the current facility, and a proposed future facility in which the uncertainty of the measurement has been driven down to a practical limit. The bias errors of the three facilities are determined to be ±0.535%, ± 0.495% and ±0.301%, respectively (to 95% confidence). The corresponding precision uncertainties are ±0.028%, ±0.025% and ±0.025%, respectively. The extremely low precision uncertainty in particular allows very small changes in capacity to be resolved. This, combined with rapid interchangeability of test modules, allows studies of the sensitivity of capacity to secondary influences with much greater flexibility than was previously possible. Consideration is also given to the definition of vane capacity in systems with several streams at different conditions of inlet total pressure and temperature. A typical high pressure (HP) NGV has three distinct streams: a mainstream flow; coolant flow ejected from film cooling holes (distributed over the vane surface); and trailing edge coolant ejection. Whilst it is helpful for the coolant mass flow rates and inlet temperatures to be included in the definition, only a relatively small difference arises from the way in which this is achieved. Several definitions appear to share similar usefulness in terms of their robustness to changing inlet conditions of individual streams, but the favoured definition offers the possibility of isolating sensitivities to key effects such as trailing edge coolant ejection. This is achieved by explicitly expressing vane capacity as a function of two controlling pressure ratios. The overall purpose of this paper is to review and analyse in detail the current state-of-the-art in gas turbine flow capacity measurement.

Hypersonic vehicle design requires mitigation of the high heat fluxes present in regions of shock-wave/boundary-layer interactions. A candidate technology that may be applied locally to these regions is transpiration cooling. In this work, experiments were conducted in the University of Oxford’s high-density tunnel at Mach 6.1 in both laminar and turbulent undisturbed boundary-layer regimes where a 10 deg shock generator impinged a strong oblique shock wave onto a transpiration-cooled microporous injector. For the laminar boundary layer, due to the strength of the incident shock, a transitional shock-wave/boundary-layer interaction region was formed with peak heating over 50 times greater than the nominal laminar level. Both nitrogen and helium were used as coolants. Relatively low levels of helium injection of [Formula: see text] for the transitional and [Formula: see text] for the turbulent scenarios were sufficient to reduce the heat transfer downstream of shock interaction to approximately 50% of the value without cooling. In fact, helium is highly effective with a similar cooling performance achieved as eight times the equivalent mass flux of nitrogen. The experimental data are correlated, and both the turbulent and transitional shock-impingement scenarios display a similar trend of reduced surface heat transfer with higher blowing parameters. Empirical fits are proposed that may be used for initial systems design.

Fluidic thrust vectoring (FTV) offers a novel approach to aerodynamic control, circumventing some of the issues associated with mechanical systems. One method is shock vector control which involves injecting a fluid into the exhaust nozzle of an engine to redirect the gases and thus, produce a control force. An experimental model which incorporated FTV was designed and tested at Mach 6 in the Oxford high density tunnel (HDT). The model was a simplified two-dimensional scramjet geometry with two different configurations to compare an internal and external exhaust nozzle. The FTV injection system consisted of a slot at the rear edge of the exhaust nozzle fed from an internal plenum. In the experimental campaign, a range of gas injection pressures and free stream stagnation pressures were tested to assess the effectiveness of both configurations. Two new measurement methods were successfully implemented in the HDT: pressure sensitive paint and a 6-axis load cell. The FTV system has been shown to be effective with observable increases in lift and pitching moment. A linear relation between the injection pressure ratio and the control forces could be observed for both configurations. Graphical abstract