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Abstract: To analyze the procedure of gasdynamically generating nanoparticles, the turbulent mixing of the heavy gas tetraethoxysilane (TEOS - ) in a hot accelerated transonic air co-flow is numerically investigated. The precursor gas TEOS is premixed with nitrogen and then ejected through circular holes in the base of an injector into the subsonic region of a nozzle flow at a co-flow Mach number of and a temperature of . A multi-species large-eddy simulation (LES) capturing the most energetic turbulent scales is used to simulate the mixing process. Close behind the blunt trailing edge of the injector the results show the mixing to be dominated by pronounced free shear layers. Downstream of the injector the flow field is accelerated to supersonic speed and dominated by trailing vortices, which transport the partially mixed precursor gas but do not enhance further mixing. The analysis of the simulation results indicates that no further mixing occurs approximately 16 trailing edge thicknesses downstream of the trailing edge. [Copyright &y& Elsevier]

The over-tip casing of the high-pressure turbine in a modern gas turbine engine is subjected to strong convective heat transfer that can lead to thermally induced failure (burnout) of this component. However, the complicated flow physics in this region is dominated by the close proximity of the moving turbine blades, which gives rise to significant temporal variations at the blade-passing frequency. The understanding of the physical processes that control the casing metal temperature is still limited and this fact has significant implications for the turbine design strategy. A series of experiments has been performed that seeks to address some of these important issues. This article reports the measurements of time-mean heat transfer and time-mean static pressure that have been made on the over-tip casing of a transonic axial-flow turbine operating at flow conditions that are representative of those found in modern gas turbine engines. Time-resolved measurements of these flow variables (that reveal the details of the blade-tip/casing interaction physics) are presented in a companion paper. The nozzle guide vane exit flow conditions in these experiments were a Mach number of 0.93 and a Reynolds number of 2.7 × 106 based on nozzle guide vane mid-height axial chord. The axial and circumferential distributions of heat transfer rate, adiabatic wall temperature, Nusselt number and static pressure are presented. The data reveal large axial variations in the wall heat flux and adiabatic wall temperature that are shown to be primarily associated with the reduction in flow stagnation temperature through the blade row. The heat flux falls by a factor of 6 (from 120 to 20 kW/m2). In contrast, the Nusselt number falls by just 36% between the rotor inlet plane and 80% rotor axial chord; additionally, this drop is near to linear from 20% to 80% rotor axial chord. The circumferential variations in heat transfer rate are small, implying that the nozzle guide vanes do not produce a strong variation in casing boundary layer properties in the region measured. The casing static pressure measurements follow trends that can be expected from the blade loading distribution, with maximum values immediately upstream of the rotor inlet plane, and then a decreasing trend with axial position as the flow is turned and accelerated in the relative frame of reference. The time-mean static pressure measurements on the casing wall also reveal distinct circumferential variations that are small in comparison to the large pressure gradient in the axial direction. [Copyright &y& Elsevier]

This article reports the measurements of time-resolved heat transfer rate and time-resolved static pressure that have been made on the over-tip casing of a transonic axial-flow turbine operating at flow conditions that are representative of those found in modern gas turbine engines. This data is discussed and analysed in the context of explaining the physical mechanisms that influence the casing heat flux. The physical size of the measurement domain was one nozzle guide vane-pitch and from -20% to +80% rotor axial chord. Additionally, measurements of the time-resolved adiabatic wall temperature are presented. The time-mean data from the same set of experiments is presented and discussed in Part I of this article. The nozzle guide vane exit flow conditions in these experiments were a Mach number of 0.93 and a Reynolds number of 2.7 × 106 based on nozzle guide vane mid-height axial chord. The data reveal large temporal variations in heat transfer characteristics to the casing wall that are associated with blade-tip passing events and in particular the blade over-tip leakage flow. The highest instantaneous heat flux to the casing wall occurs within the blade-tip gap, and this has been found to be caused by a combination of increasing flow temperature and heat transfer coefficient. The time-resolved static pressure measurements have enabled a detailed understanding of the tip-leakage aerodynamics to be established, and the physical mechanisms influencing the casing heat load have been determined. In particular, this has focused on the role of the unsteady blade lift distribution that is produced by upstream vane effects. This has been seen to modulate the tip-leakage flow and cause subsequent variations in casing heat flux. The novel experimental techniques employed in these experiments have allowed the measurement of the time-resolved adiabatic wall temperature on the casing wall. These data clearly show the falling flow temperatures as work is extracted from the gas by the turbine. Additionally, these temperature measurements have revealed that the absolute stagnation temperature within the tip-gap flow can be above the turbine inlet total temperature, and indicates the presence of a work process that leads to high adiabatic wall temperatures as a blade-tip passes a point on the casing wall. It is shown that this phenomena can be explained by consideration of the flow vectors within the tip-gap, and that these in turn are related to the local blade loading distribution. The paper also assesses the relative importance of different time-varying phenomena to the casing heat load distribution. This analysis has indicated that up to half of the casing heat load is associated with the over-tip leakage flow. Finally, the implications of the experimental findings are discussed in relation to future shroudless turbine design, and in particular the importance of accounting for the high heat fluxes found within the tip-gap. [Copyright &y& Elsevier]