The paper presents the results of an activity carried out on a three-bladed inducer and compares the experimental data from other similar inducers. All the inducers considered in the present study have been designed by means of the simplified analytical model recently developed by some of the authors. The main effects of different geometrical solutions on hydraulic performance and flow instabilities of the pumps under noncavitating and cavitating conditions are presented in the paper
This experimental study explored the response of burning liquid fuel droplets to one-dimensional acoustic standing waves created within a closed, atmospheric waveguide. Building upon prior droplet combustion studies quantifying mean and temporal flame response of several alternative fuels to moderate acoustic excitation (Sevilla-Esparza, et al., Combustion and Flame, 161(6):1604–1619, 2014), the present work focused on higher amplitude acoustic forcing observed to create periodic partial extinction and reignition (PPER) of flames enveloping the droplet. Detailed examination of ethanol droplets exposed to a range of acoustic forcing conditions (frequencies and amplitudes in the vicinity of a pressure node) yielded several different combustion regimes: one with sustained oscillatory flames, one with PPER, and then full extinction at very high excitation amplitudes. Phase-locked OH* chemiluminescence imaging and local temporal pressure measurements allowed quantification of the combustion-acoustic coupling through the local Rayleigh index. Similar behavior was observed for JP-8 and liquid synthetic fuel derived via the Fischer-Tropsch process, but with quantitative differences based on different reaction time scales. Estimates of the mean and oscillatory strain rates experienced by the flames during excitation assisted with interpreting specific relationships among acoustic, chemical, and fluid mechanical/straining time scales that can lead to a greater understanding of PPER.
The experimental characterization of the rotordynamic fluid forces acting on a whirling centrifugal impeller have been investigated at different flow rates and cavitating conditions. The recently developed method for continuously measuring the rotordynamic forces at variable whirl ratios has been readapted and successfully applied for measuring the same forces at constant whirl ratio but variable cavitation number. The flowrate has a major influence on the stability of the rotordynamic forces at positive whirl ratios where a threshold flowrate separates the stable zone from the unstable. At negative whirl ratios, the normal force is typically unstable independently on the flow rate. Cavitation has always a destabilizing effect at positive whirl ratio while it can stabilize the rotordynamic forces at negative whirl ratio.
A number of platinum catalysts for the decomposition of 98% hydrogen peroxide, based on different substrates, geometries, and sizes, have been prepared using different procedures. The catalysts have undergone a set of dedicated tests for screening their catalytic activity and their thermomechanical resistance in order to identify the most efficient and suitable catalyst to be used for a pulsed monopropellant propulsion system. An experimental test campaign on a 20 N monopropellant thruster prototype has been carried out with the aim of assessing the capability of the finally selected new Pt∕α-Al 2 O 3 catalysts of effectively decomposing 98% hydrogen peroxide and the attainable propulsive performance in steady-state conditions for the future assessment of the propulsive performance of the intrinsically unsteady new propulsion concept. The catalysts have been able to decompose up to 1 liter of 98% H 2 O 2 with very good efficiencies (hc > 95% and hΔT ≥ 90%) and without any pellet breakage or catalytic degradation. The thrust profile has been particularly smooth and the experimental specific impulse measured at sea level with the matched conical nozzle has been 130 s, which corresponds to an extrapolated vacuum specific impulse for a high-expansionarea-ratio bell-contoured nozzle higher than 185 s. Nomenclature A = catalytic bed cross-sectional area, which is equal to= theoretical thrust coefficient, which is equal to γ 2∕γ1 γ1∕γ−1 2∕γ−11−p e ∕p C γ−1∕γ p p e −p a ∕p C A e ∕A t fγ; A e ∕A t ; p a ∕p C c = characteristic velocity, which is equal to p C A t ∕m, m∕s c theo = theoretical characteristic velocity, which is equal to which is equal to RT∕γ p γ1∕2 γ1∕2γ−1 , m∕s D = catalytic bed diameter, m D e = nozzle exit diameter, m D t = nozzle throat diameter, m F = thrust, N G = bed load or mass flux, which is equal to m∕A, kg∕s · m 2 g = gravitational acceleration at sea level, m∕s 2 I sp = specific impulse, which is equal to F∕mg, s I sp exp vacuum = vacuum specific impulse extrapolated from the experimental results, s L = catalytic bed length, m m = propellant mass flow rate, kg∕s or g∕s p C = chamber pressure, Pa or bar p CATBEDinlet = inlet catalytic bed pressure, Pa or bar p ENGINEinlet = inlet engine pressure (after the firing valve and before the injector), Pa or bar p TANK = tank pressure, Pa or bar R = gas constant of the exhaust gases, J∕kg · K S BET = specific surface area, m 2 ∕g T ad = adiabatic decomposition temperature, K or°C T amb = ambient temperature, K or°C T C = combustion chamber temperature, K or°C T i = initial temperature, K or°C T TANK = propellant temperature inside the tank, K or°C T 3;4 = temperatures at different stations along the bed, K or°C t max = time to reach the peak temperature, s t 90% = thrust rise time, s α conical = conical half angle, deg γ = specific heat ratio of the exhaust gases Δp CATBED = pressure drop across the catalytic bed, which is equal to p CATBEDinlet −p C , Pa or bar Δp ENGINE = pressure drop across the engine, which is equal to p ENGINEinlet − p C , Pa or ba...
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