An experimental investigation of a confined rectangular jet in crossflow was performed. The rectangular jet is highly confined in that it spans almost 80% of the crossflow duct, rather than issuing into a semi-infinite crossflow. Furthermore, the jet is confined in the cross-stream direction because it issues into a relatively narrow duct. In addition, the flow rate of the secondary jet is large (up to 50% of the crossflow flow rate) which also influences the jet–crossflow interaction. Configurations of this type are found in a variety of different industrial manufacturing processes used to mix product streams.A systematic variation of three pertinent parameters, i.e. momentum ratio, injection angle and development length, was performed. A full factorial experiment was run using three velocity ratios ($Vr\,{=}\,0.5, 1.0, 1.5$), three downstream distances ($x/D_{h}\,{=}\,6, 10, 19$) and six injection angles ($\alpha\,{=}\,18^\circ, 24^\circ$, 30^\circ, 48^\circ, 60^\circ, 90^\circ$). A planar Mie scattering mixing diagnostic system was used to evaluate the relative mixing effectiveness at various conditions within the parameter space studied. Three regimes for the jet–crossflow interaction and the resulting scalar concentration field were revealed: ‘wall jet’, ‘fully lifted jet’ and ‘reattached jet’. To understand the flow physics in these regimes, a more detailed exploration of the secondary flow and coherent structures was required. This was accomplished by acquiring velocity field data at measurement locations and conditions that demarcate the different regimes ($\alpha\,{=}\,30^{\circ}$ and $48^{\circ}, Vr\,{=}\,1.0$ and 1.5, $x/D_{h}\,{=}\, 3, 6, 10$, 15 and 19) using a laser-Doppler velocimetry (LDV) system. The combined scalar concentration and velocity field data provided an understanding of the large-scale mixing and the role of coherent structures and their evolution. The investigation revealed that the flow does not necessarily develop symmetrically and also highlighted some of the effects of confinement.

As global demand for energy increases while environmental regulations tighten, novel power generation cycles are being developed to meet market needs while accommodating green requirements. The Allam cycle is an approach (with high pressure, low pressure ratios, oxygen-fuel combustion and CO2 as a working fluid) that efficiently produces power in a compact plant, avoids NOx emissions, makes efficient use of clean-burning methane (natural gas) and can generate high-pressure carbon dioxide for enhanced oil and gas recovery in the field. The cycle requires oxy-fuel-CO2 combustion at approximately 30MPa and 1150° C turbine inlet temperatures. Due to its relatively compact size (owing to the high operating pressures), the Allam cycle technology can be implemented for a low cost in relative existing power plants, and given the current economic climate, natural gas is the most financially appealing application. Meeting environmental regulations for decades to come, the cycle can dramatically lower the cost of electricity. The critical path for plant implementation lies in demonstrating efficient, stable combustion at 30MPa. Similar pressures have been demonstrated in rocket engine systems, where reusability typically means 3 to 4 hot fires and surviving 8 to 32 minutes lit. The technical challenge here lies in designing durable hardware capable of thousands of hours of continuous operation and efficient combustion over the range of conditions required in a power plant. Production of clean CO2 exhaust (ideally, free of O2 and CO) is another challenge that will drive plant viability.

A full-field planar optical diagnostic technique for V0 studying mixing in swirling flows is described. Results were obtained using this technique to provide planar mixing information by seeding a simulated fuel stream with aluminum ~brel oxide particles, then inferring concentration from Mie scatter-# ing intensity distributions. This facility and measurement pp technique are unique for several reasons. First, they allow r spatial variations in laser sheet energy to be corrected for on rf a shot-to-shot basis. Second, they allow experiments to be zp performed for swiders with practical fuel and oxidizer flow rates, i.e. on the order of 150 g/s (0.33 lbm/s). Finally, they allow full size swirler models to be evaluated, with the entire exit plane imaged simultaneously. Representative results are presented as false color images of the planar mixing fields. These images allow rapid assessment of the mixing process and its changes with variations in operating conditions or swirler geometry.List of symbols C seed particle concentration, m -3 mean component of seed particle concentration, m-3 C' fluctuating component of seed particle concentration, m-3 C* time averaged ratio of rms particle concentration fluctuations to average particle concentration, dimensionless dp particle diameter, m I laser energy after passing through the flow, Jim 2 r mean laser energy, l/m 2 I0 laser energy before passing through the flow, J/m 2 L~ eddy length scale, m l laser beam path length, m U~ eddy velocity scale, m/s V diode voltage reading after passing through the flow, V 17 mean diode voltage, V

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The typical permissible overspeed limit is about 5-7% of design mechanical speed. Thus fan-corrected speed needs to be reduced if its mechanical speed exceeds the limiting value. It will alter the engine steady-stateperformance,and the optimum system de nition as obtained earlier will also change.To investigate this issue, another optimization study was performed in which the fan mechanical speed was limited to 1.07 times its design speed. It results in W TO and W ENG;SLS that are of the same order of magnitude as at the conventional design point.As design Mach number increases at H D 9:0 km., optimum TR begins to decrease. This is because the increase in design Mach number causes the T 1;DP and, hence, TET DP also to increase, which reduces TR. There is a ight point, which is M D 1:55 in the present case, at which TR equals 1.0. If a higher Mach number, e.g., 1.60, is chosen as the design point, the optimum value of W TO begins to increase because the least value that TR can take is 1.0. Thus as design Mach number increases, TET max occurs at a higher Mach number (or T 1;DP ), and the engine operates at relativelyreduced TET at a large number of ight points, where Mach number (or T 1 ) is lower than that of the design point.Though not investigated,the trends as observed at design altitude of 9.0 km should also hold true at other design altitudes, because any designcombinationof H=M can be translatedinto an equivalent T 1;DP , which then dictates the quality of chosen ight point as the engine designpoint. As a typical example,cycle optimizationresults at H D 6:0 km/M D 1:3 in ISA at DT amb D 0 K (T 1;DP D 333 K) are not signi cantly different in comparison to that at H D 9:0 km/M D 1:5 in ISA at DT amb D 0 K, which also corresponds to T 1;DP D 333 K.To summarize, at a prescribed design altitude there is a lower limit on T 1;DP , below which (despite a lower value of optimum W TO ) the resulting cycle is not practically feasible. There also exists an upper limit on T 1;DP beyond which cycle optimization results in an increased optimum W TO . Between these limits of T 1;DP , cycle optimization, results do not differ signi cantly within themselves and in comparison with that at the conventional design point. Thus instead of searching for an optimum design point, it is suf cient to perform conceptual design system optimization at the conventional engine design point. ConclusionsThe value that T 1;DP takes at an H=M combination dictates its suitability as the engine design point. If minimization of W TO is the criteria for engine cycle optimization, then a ight condition with a low T 1;DP is more suited as the design point because it results in a lower value of optimum W TO . However, it also requires the engine to overspeed continuously for long durations, thereby causing an increased engine weight and reduction in the life of the rotating components. If this overspeeding is restricted to the current design limits of about 7% of design speed, savings in W TO diminish.As T 1;DP increases, there arises a ight point at ...