Neutron reflection has been used to measure the surface excesses of two poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers (EPE) at the air/water interface over a range of bulk solution concentrations. The copolymers, of approximate formulas E23P52E23 and E9P22E9 and have similiar adsorption isotherms in terms of their molar adsorption, though quite different in terms of segmental adsorption. The isotherms have two steps, one at low concentrations leading to a plateau over about two decades of concentration followed by a substantial rise over the decade of concentration leading to the critical micelle concentration. In the plateau region, the area per ethylene oxide segment was found to be about 9 and 22 Å2 respectively for the two copolymers decreasing to 6.5 and 12 Å2 at the CMC at 25 °C. The thickness of the adsorbed layer showed little change between these two coverages. An increase in temperature to 35 °C shifted the adsorption isotherm pattern to concentrations about 1/30 of those at 25 °C, in line with the change in CMC. The neutron surface excesses were incorporated into the integrated Gibbs equation and fitted the surface tension curves well over most of the range of adsorption. However, a sharp change in surface tension at low polymer concentrations (about 10-3 wt/vol %) was found not to be consistent with the neutron measurements, and a model of the surface tension behavior in this region, based on adsorption from a polydisperse sample, has been proposed to explain this behavior. Earlier explanations of this surface tension behavior are shown to be inconsistent with the neutron reflection and surface tension results.

Neutron reflection has been used to investigate the structure of adsorbed layers of two triblock copolymers with approximate formulas E 23 P 52 E 23 and E 9 P 22 E 9 , where E is ethylene oxide and P is propylene oxide. Measurements were made at the air/water interface at the critical micelle concentration and at two much lower concentrations, and at temperatures of 25 °C and 35 °C. Isotopic labeling was used to improve the resolution of the experiment. In general, the adsorbed layer can be described in terms of a minimum of four uniform sublayers. The outermost layer is always a water-free layer containing only propylene oxide (PO) residues. The ethylene oxide (EO) residues form a tail below this layer, which extends into the solution over a distance slightly shorter than the fully extended length. Depending upon the conditions, some PO is also mixed in with this tail region. For example, at the lower surface concentrations, the segment density of the (PO) decays rapidly and there is a relatively small proportion of PO immersed in the water but, at the highest concentrations, there is a much larger amount of PO in the aqueous/EO region, and this extends some way into the solution. At the higher temperature, there is little PO in the aqueous region of the layer, but there is significant mixing of PO with EO in a sublayer just below the main PO layer out of the water. The smaller molecular weight polymer gives a much more disordered structure with greater mixing of all three components. The disorder in these adsorbed layers is higher than that previously suggested for the micellar structure. Comparison of the layer structure at the air/water interface with that in micelles indicates either that there is a significant difference in the extent of mixing of the PO and EO between the two situations or that the published small-angle scattering data can be reinterpreted in terms of a micellar structure where the PO/EO mixing is more in accord with that observed at the air/water interface.

This paper presents the performance of pressure-sensitive paint (PSP) for the direct measurement of species concentration on a porous surface with mass injection. It is used to measure the ability of an injected gas to reduce the mass transfer of freestream species to the surface. A porous alumina sample was sprayed with a PSP luminophore solution. The sample was installed into a flat plate model and exposed to hypersonic cross-flows in the Oxford High-Density Tunnel. Tests were conducted with no coolant injection, air injection, and nitrogen injection at increasing blowing ratios. Oxygen partial pressure maps on the transpiration-cooled surface were obtained for several conditions at unit Reynolds numbers between $$2.58{-}5.0 \times 10^7/ \mathrm{m}$$ 2.58 - 5.0 × 10 7 / m and blowing ratios between $$0.016{-}0.078\%$$ 0.016 - 0.078 % . The oxygen pressure decreases as the unit Reynolds number decreases and the blowing ratio increases. Graphic abstract

High pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance. Measurements are performed on a linear cascade of high pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analysed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.