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The article illustrates the application of Bayesian estimation to the identification of flow instabilities, with special reference to rotating cavitation, in a three-bladed axial inducer using the unsteady pressure readings of a single transducer mounted on the casing just behind the leading edges of the impeller blades. The typical trapezoidal pressure distribution in the blade channels is parametrized and modulated in time and space for theoretically reproducing the expected pressure generated by known forms of cavitation instabilities (cavitation auto-oscillations, n-lobed rotating cavitation, higher-order surge/rotating cavitation modes). The Fourier spectra of the theoretical pressure so obtained in the rotating frame are transformed in the stationary frame, frequency broadened to better approximate the experimental results, and parametrically fitted by maximum likelihood estimation to the measured auto-correlation spectra. Each form of instability generates a characteristic distribution of sidebands in addition to its fundamental frequency. The identification makes use of this information for effective detection and characterization of multiple simultaneous flow instabilities with intensities spanning over about 20 dB down to about 4 dB signal-to-noise ratios. The same information also allows for effectively bypassing the aliasing limitations of traditional cross-correlation methods in the discrimination of multiple-lobed azimuthal instabilities from dual-sensor measurements on the same axial station of the machine. The method returns both the estimates of the model parameters and their standard deviations, providing the information needed for the assessment of the statistical significance of the results. The proposed approach represents therefore a promising tool for experimental research on flow instabilities in high-performance turbopumps.

The article illustrates the results of an exploratory study on the effectiveness of maximum likelihood Bayesian estimation in the identification of cavitation instabilities in axial inducers using the blade-to-blade pressure measured by a single transducer flush-mounted on the impeller casing. The typical azimuthal distribution of the pressure in the blade channels is parameterized and modulated in space and time for theoretically reproducing the expected pressure generated by known forms of cavitation instabilities (cavitation surge auto-oscillations, n-lobed synchronous/asynchronous rotating cavitation, and higher-order surge/rotating cavitation modes). The power spectra of the theoretical pressure so obtained in the rotating frame are transformed in the stationary frame, corrected for frequency broadening effects, and parametrically fitted by maximum likelihood estimation to the measurements of the pressure on the inducer casing just downstream of the blade leading edges. In addition to its fundamental frequency, each form of instability generates a characteristic spectral distribution of sidebands. The identification uses this information for successfully discriminating flow oscillation modes occurring simultaneously with intensities differing by up to one order of magnitude. The method returns the estimates of the model parameters and their standard errors, allowing one to assess the accuracy and statistical significance of the identification. The results first demonstrate that elementary maximum likelihood Bayesian identification is indeed capable to effectively detect and characterize the occurrence of flow instabilities in cavitating inducers at a fraction of the experimental and postprocessing costs and complexities of traditional cross-correlation methods.

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-Al2O3 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% H2O2 with very good efficiencies (hc*>95% and hΔT≥90%) and without any pellet breakage or catalytic degradation. ...

After a brief review of the fundamental aspects of cavitation relevant to the operation of high-performance inducers and turbopumps, the article summarizes their application to the analysis of pumping systems, illustrates the scaling of cavitation phenomena from model tests to full-scale operation, describes the occurrence of flow-induced instabilities in turbomachinery, and introduces the concepts of static and dynamic instability of pumping systems and their generalization to cavitating turbopump systems.

A reduced-order model for the preliminary design and performance prediction of radial turbopumps is illustrated. The model expresses the 3D, incompressible, inviscid, irrotational flow through helical blades with slow axial variations of their pitch and backsweep angles by superposing a 2D axial vorticity correction to a fully guided forced vortex flow with axisymmetric stagnation velocity in the meridional plane. Application of the relevant governing equations allows for the closed-form definition of the impeller geometry and flowfield in terms of a reduced number of controlling parameters. Mass and momentum conservations are used for coupling the flow leaving the impeller with the 2D reduced-order models of the flow in the diffuser and/or the volute, as well as for the evaluation of the mixing losses in the transfer between successive components of the machine. This information completes the geometric definition of the turbopump and determines its ideal noncavitating performance in accordance with the resulting flowfield. As a consequence of the neglect of viscous effects, the slip factor predicted by the present model exceeds those obtained from theoretical/semi-empirical formulas reported in literature for centrifugal pumps, but correctly captures their trend.

The article reviews the main forms of flow-induced instabilities detected in the liquid propellant turbopumps systems of modern rocket engines, with special reference to rotating stall, rotating cavitation, cavitation surge and higher order surge modes, illustrating their characteristics, origin and damage potential.

The experimental characterization of the rotordynamic fluid forces acting on a whirling centrifugal impeller has 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.

The present paper illustrates a comprehensive experimental campaign carried out in order to assess the capability of four especially developed catalytic beds to decompose hydrogen peroxide under operational conditions representative of typical application to small monopropellant rocket engines and to characterize the resulting performance of the thruster. The catalytic beds have been integrated in a reconfigurable thruster prototype and tested in a suitable test facility. All beds have shown high decomposition and propulsive efficiencies, well in excess of 90%. In particular, two catalytic beds (indicated as LR-III-106 and CZ-11-600) have been, respectively, able to decompose up to 13 and 11 kg of 90%hydrogen peroxide (equivalent to 433 and 366 g of decomposedH2O2 per gram of catalyst) in 2500 and 2000 s of continuous thruster operation. They exhibited C-star efficiencies higher than 95%. The experimental results have also indicated two main sources of catalyst degradation. In low-porosity catalysts the decay of chemical activity affects the temperature efficiency and causes theflooding of thefirst portion of the catalytic bed,whereas highly porous catalysts experience thermal rupture of the carrier,which leads to excessive growth of the pressure drop across the catalytic bed.

The present paper illustrates different firing tests carried out on advanced catalytic beds for hydrogen peroxide decomposition in a new monopropellant thruster prototype designed for easier adjustment and control of the main operational and propulsive parameters. The tests refer to the comparison between a pt/α-Al 2 O 3 catalyst (named FC-LR-87) and a similar commercially available space propulsion catalyst. Up to 2 kg of 87.5 % hydrogen peroxide have been decomposed by a single sample of the FC-LR-87 catalyst. Both steady-state and pulsed firings have been carried out in the same reactor configuration. A fresh sample of the FC-LR-87 catalyst has also been tested at a different bed load. Both the FC-LR-87 and the commercial catalysts showed equivalent propulsive performances, with a slightadvantage in favor of the FC-LR-87 catalyst in terms of the c* and temperature efficiencies (up to 94 and 93%, respectively).

PulCheR is a R&D project funded by the European Union Seventh Framework Programme with the main aim of demonstrating the feasibility of a new propulsion concept in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses. The characterization of this type of thruster has required to carefully design the test bench in order to allow the right assessment of the thruster performance. The unsteady behavior of the thruster has been the main difficulty during the design and the choice of transducers. The most difficult measurement concerns the assessment of the mass injected at each pulse inside the thruster. Because of this, two distinct test benches have been designed and two approaches at measuring the mass injected have been considered. The present article focuses on the challenges concerning the design of the test bench for the characterization of the PulCheR monopropellant thruster.

PulCheR (Pulsed Chemical Rocket with Green High Performance Propellants) is a research project co-funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n°313271 and is at its second year. The project officially started as of January 1st, 2013, and is mainly aimed at demonstrating the feasibility of a pulsed propulsion system in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses, reproducing the defence mechanism of a notable insect: the bombardier beetle. The feasibility of this concept is under study and many activities have been already performed. The PulCheR monopropellant thruster is already ready for being tested, whereas more difficulties concern the application of PulCheR to the bipropellant configuration, even if the selected propellants, HTP and propyne show very interesting performance. As an added value, the new propulsion concept investigates green propellants. The present paper aims at presenting the state of the art of the project after two years since the beginning

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.

In the present paper, the results from an extensive experimental characterization of the rotordynamic forces acting on a whirling three-bladed, tapered-hub, variable-pitch inducer are presented. The campaign has been conducted in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at ALTA S.p.A. The forces acting on the impeller have been measured by means of a rotating dynamometer mounted just behind the inducer. The roles of the rotor whirl motion, flow rate, cavitating condition, and liquid temperature have been investigated. The analysis has been conducted by means of the classical rotordynamic approach together with a recent experimental technique, consisting in measuring the rotordynamic forces continuous behavior (spectra) as functions of the whirl excitation frequency. This technique allows for evaluating information from experiments more rapidly and accurately with regards to previous methods. Therefore, it is useful to better capture the complexity of the rotordynamic forces and assess their consequences on the stability of axial inducers.

The present paper illustrates the main results of an experimental campaign conducted in the Cavitating Pump Rotordynamic Test Facility. The tests were carried out on the FAST2 inducer, a two-bladed axial pump designed and manufactured using the criteria followed for VINCI180 inducer. The transparent inlet section of the facility was instrumented by several piezoelectric pressure transducers located at three axial stations: inducer inlet, outlet and at the middle of the axial chord of the blades. For each axial station at least two transducers were mounted at selected angular spacing, in order to cross correlate their signals for coherence and phase analysis. The most interesting detected instabilities were: a cavitation auto-oscillation at about 5-12 Hz, a high-order cavitation surge at a frequency of about 4.4Ω and a rotating stall at about 0.31Q. Some experiments were carried out under forced vibration conditions: it was observed that a whirl frequency of about 1 Hz can provide excitation for violent surge-mode oscillations. A "cavitation surge" instability was also observed at higher whirl frequencies.

The present paper illustrates and discusses the first results of the characterization of the dynamic transfer matrix of cavitating turbopumps by means of a series of forced-vibration tests carried out on a high-head three-bladed inducer in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at Alta, Pisa, Italy. The flow has been excited by vertically vibrating with adjustable frequency and intensity the free-surface tank used to close the loop of the suction and discharge lines of the inducer. The pressure and flow rate fluctuations for the determination of the dynamic transfer matrix have been obtained from unsteady pressure measurements at suitable locations on the inlet/outlet lines of the inducer. Two loop configurations with different inlet/outlet impedances to/from the test inducer have been used in order to obtain at each excitation frequency a set of four linearly independent measurements for the detetermination of the four elements of the dynamic transfer matrix. The preliminary results are in qualitative agreement with the scant data available in the literature for comparable inducers.

PulCheR (Pulsed Chemical Rocket with Green High Performance Propellants) is a new propulsion concept in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses, reproducing the defence mechanism of a notable insect: the bombardier beetle. The radical innovation introduced by PulCheR is the elimination of any external pressurizing system even if the thruster works at high pressure inside the combustion chamber. At each pulse, pressurization of the combustion chamber gases takes place due to the decomposition or combustion reaction, and the final pressure is much higher than the one at which the propellants are stored. The weight of the feeding system is significantly reduced because the propellants are fed at low pressure, and there is no need for turbopumps, high pressure propellant tanks or gas vessels. The feed pressure becomes independent on the chamber pressure and the performance degradation typical of the blow down mode in monopropellant thrusters can be avoided. The PulCheR concept is able to substitute many currently used propulsion systems for accessing space in both mono and bipropellant configurations. The preliminary assessment of this new propulsion concept has been investigated using green propellants with potential similar performance to the current stateof-the-art for monopropellant and bipropellant thrusters.

The paper shows the results of an experimental campaign conducted in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at ALTA S.p.A., aimed at characterizing the cavitation thermal effects on two tapered-hub, variable-pitch inducers, designated as DAPAMITO. The semi-empirical method proposed by Ruggeri and Moore for scaling the thermal cavitation effects has been successfully applied and, consequently, a further validation of this method has been provided. The influence of the temperature on the intensity of the performance degradation associated with the attached cavitation instability has been identified as a new typology of cavitation thermal effects. In this case, the inhibition of the bubble growth due to thermal effects can be detected by the reduction of the performance degradation usually associated with this type of instability.Copyright © 2011 by ASME

The present paper illustrates the results of an experimental campaign conducted in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at ALTA S.p.A. aimed at characterizing the rotordynamic forces acting on two different whirling tapered-hub, variable-pitch axial inducers. The forces acting on the impeller have been measured by means of a rotating dynamometer mounted just behind the inducer. The roles of the imposed whirl motion of the rotor, flow coefficient, cavitation number, and liquid temperature have been investigated. The destabilizing role of cavitation has been confirmed. The experimental results are consistent with previous experimental campaigns documented by the open literature, including the former data published by Caltech researchers. The observed dependence of the tangential and normal components of the rotordynamic force on the whirl-to-rotational speed ratio does not follow the quadratic functional behavior often assumed in the open literature. Rotordynamic forces of large amplitude and destabilizing nature especially occur in the presence of cavitation, potentially compromising the stability of the pump operation.

The paper illustrates the results of an experimental campaign conducted in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at ALTA S.p.A., aimed at characterizing the rotordynamic forces acting on a whirling four-bladed, tapered-hub, variable-pitch inducer, designated as DAPAMITO4. The roles of the imposed whirl motion of the rotor, flow coefficient, cavitation number and liquid temperature have been investigated. A novel experimental technique, consisting in measuring the continuous spectra of the forces as functions of the whirl ratio, has been developed and validated. This technique gives the possibility of extracting valuable information from the experiments by clearly identifying the qualitative and quantitative behavior of the forces, and is therefore useful to catch the unlikely foreseeable complexity of the rotordynamic forces and their consequences on the stability of axial inducers.Copyright © 2011 by ASME

The paper describes a reduced-order analytical model for the characterization of the dynamic transfer matrix of complex test setups including cavitating pumps. The model, even if based on several simplifying assumptions (quasi 1-dimensional flow, small oscillations, incompressible working fluid, quasi-static response of all the components of the system), is able of providing good indications about the order of magnitude of the expected pressure and flow rate oscillations in the system under given flow conditions and, more in general, about the experiment design. The model has been applied to Alta’s Cavitating Pump Rotordynamic Test Facility with the custom-designed DAPAMITO3 axial inducer, in order to start the design process of an experiment for the characterization of the inducer dynamic matrix. It has been found that a good mechanism for providing an external excitation to the facility can be represented by a device able of mechanically vibrating the water tank in a vertical direction, while the most suitable way for obtaining the second linearly independent test configuration, needed for the experimental characterization of the cavitating pump dynamic matrix, is represented by a variation of the suction line inertance. Finally, it has been shown that it is possible to measure the flow rate oscillations in the suction and discharge lines by means of the difference between the measurements taken by two pressure transducers, placed at two different sections of the relevant pipe line.

onset of a number of flow instabilities and the marked increase of the pressure drop in the decomposition bed led to a severe decrease of the engine thrust. In order to take proper action for enhancing the thermal shock resistance of the catalyst bed it has been necessary to better understand the dynamics of the heat transfer between the decomposing propellant and the catalyst support. In this work a reduced order model of the thermal transient and the associated thermal stresses in the catalyst pellets is presented. The indications provided by the model have therefore been used for orienting the selection of a suitable catalyst carrier and the development of a new Pt/α–Al 2O3 catalyst, here indicated as LR-III-127. Its strength and propulsive performance have been experimentally evaluated under realistic working conditions in a HTP thruster prototype. After the decomposition of 1.5 kg of H 2O2 (90% by weight) the LR-III-127 catalyst displayed a low susceptibility to thermal cracking and outstanding performance in terms of decomposition efficiency.

The present paper describes a steady one dimensional model of the hydrogen peroxide decomposition flow in a pellet-type catalytic bed and its application to the parametric design of a typical reactor for small rocket propellant thrusters. The two-phase liquid-gas-vapor flow through the bed is treated as a homogeneous, adiabatic, chemically reacting flow, for which the properties depend on the local composition. Fast equilibrium hydrogen peroxide adsorption and first-order finite-rate desorption is assumed for the one-step hydrogen peroxide decomposition reaction on the catalyst surface. Standard viscous/aerodynamic correlations for porous media are used to account for pressure losses. The predictions of the model depend on a limited number of uncertain parameters, for which the values can be readily determined by comparison with the available experimental data. Good agreement has been attained between the model predictions and the results of hydrogen peroxide monopropellant thruster firings. The model provides a rational framework for identifying the main operational parameters of catalytic pellet beds, understanding their interactions, and efficiently guiding the reactor sizing and design, using the indications easily obtained from sensitivity analyses.

The present paper illustrates the results of an experimental campaign conducted in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at ALTA S.p.A. aimed at characterizing the rotordynamic forces acting on a whirling four-bladed, tapered-hub, variable-pitch inducer, designated as DAPAMITO4. The forces acting on the impeller have been measured by means of a rotating dynamometer mounted just behind the inducer. The roles of the imposed whirl motion of the rotor, flow coefficient, cavitation number and liquid temperature have been investigated. The destabilizing role of cavitation has been confirmed. The experimental results are consistent with previous findings obtained by the authors, as well as with former data published by Caltech researchers. The observed dependence of the tangential and normal components of the rotordynamic force on the whirl-to-rotational speed ratio does not follow the quadratic functional behavior often assumed in the open literature. Rotordynamic forces of large amplitude and destabilizing nature especially occur in the presence of cavitation, potentially compromising the stability of the pump operation.

The present paper illustrates a comprehensive experimental campaign carried out in order to assess the capability of four especially-developed catalytic beds to decompose hydrogen peroxide under operational conditions representative of typical application to small monopropellant rocket engines, and to characterize the resulting performance of the thruster. The catalytic beds have been integrated in a reconfigurable thruster prototype and tested in ALTA’s Green Propellant Rocket Test Facility. All beds have shown high decomposition and propulsive efficiencies, well in excess of 90%. In particular, two catalytic beds – indicated as LR-III-106 and CZ-11-600 – have been respectively able to decompose up to 13 and 11 kg of 90% hydrogen peroxide, equivalent to 2500 and 2000 s of thruster continuous operation, exhibiting C-Star efficiencies higher than 95%. The experimental results have also indicated two main sources of catalyst degradation. In low-porosity catalysts the decay of chemical activity affects the temperature efficiency and causes the flooding of the first portion of the catalytic bed, while highly porous catalysts experience thermal rupture of the carrier, which leads to excessive growth of the pressure drop across the catalytic bed.

A reduced order model for preliminary design and noncavitating performance prediction of tapered axial inducers is illustrated. In the incompressible, inviscid, irrotational flow approximation, the model expresses the 3D flow field in the blade channels by superposing a 2D cross-sectional vorticity correction to a fully guided axisymmetric flow with radially uniform axial velocity. Suitable redefinition of the diffusion factor for bladings with non-negligible radial flow allows for the control of the blade loading and the estimate of the boundary layer blockage at the specified design flow coefficient, providing a simple criterion for matching the hub profile to the axial variation of the blade pitch angle. Carter’s rule is employed to account for flow deviation at the inducer trailing edge. Mass continuity, angular momentum conservation, and Euler’s equation are used to derive a simple second order boundary value problem, whose numerical solution describes the far-field axisymmetric flow at the inducer discharge. A closed form approximate solution is also provided, which proved to yield equivalently accurate results in the prediction of the inducer performance. Finally, the noncavitating pumping characteristic is obtained by introducing suitably adapted correlations of pressure losses and flow deviation effects. The model has been verified to closely approximate the geometry and noncavitating performance of two space inducers tested in Alta’s Cavitating Pump Rotordynamic Test Facility, as well as the measured pumping characteristics of a number of tapered-hub inducers documented in the literature.

The present paper illustrates the firing tests recently carried out at Alta S.p.A., Pisa, Italy, on advanced catalytic beds for hydrogen peroxide (HP) decomposition in a new monopropellant thruster prototype designed for easier adjustment and control of the main operational and propulsive parameters. The tests refer to the comparison between a Pt/�Al 2O3 catalyst (named FC-LR-87) developed in collaboration with the Chemistry and Industrial Chemistry Department of Pisa University, Italy, and a similar commercially available space propulsion catalyst. Up to 2 kg of 87.5% HP have been decomposed by a single sample of the FC-LR-87 catalyst. Both steady state and pulsed firings have been carried out in the same reactor configuration. A fresh sample of the FC-LR-87 catalyst has also been tested at a different bed load. Both the FC-LR-87 and the commercial catalysts showed equivalent propulsive performances, with a slight advantage in favor of the FC-LR87 catalyst in terms of the c* and temperature efficiencies (up to 94% and 93%, respectively).

The paper introduces and briefly outlines the research activities on cavitation and turbopump hydrodynamics conducted in the last 20 years at the Department of Aerospace Engineering of Pisa University, at Centrospazio, a nonprofit space propulsion laboratory established in 1989, and at Alta S.p.A., a private spin-off company founded in 2000 and active in the aerospace sector. Both the experimental activities conducted in a dedicated facility called Cavitating Pump Rotordynamic Test Facility (CPRTF) and the analytical/numerical work is described. A valuable experience has been gained by the research group throughout the years, and important results have been obtained in the definition of experimental techniques for the detection of flow instabilities, the understanding of thermal cavitation effects on pump performance and instabilities, and the development of reduced order analytical tools for the preliminary design and performance prediction of axial inducers.

In the present paper, the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets is investigated. For this purpose, a reconfigurable test bench for the characterization of the operation and the propulsive performance of small rocket thrusters has been designed and realized. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on γ-alumina supporting spheres. The results indicated that Pt/Al 2 O 3 is an effective catalyst combination for the decomposition of 87.5% propellant-grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time, and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high-grade hydrogen peroxide (87.5 % by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental setup.

The present paper illustrates the setup and the preliminary results of an experimental investigation of cavitation flow instabilities carried out by means of a high-speed camera on a three-bladed inducer in the cavitating pump rotordynamic test facility (CPRTF) at Alta S.p.A. The brightness thresholding technique adopted for cavitation recognition is described and implemented in a semi-automatic algorithm. In order to test the capabilities of the algorithm, the mean frontal cavitating area has been computed under different operating conditions. The tip cavity length has also been evaluated as a function of time. Inlet pressure signal and video acquisitions have been synchronized in order to analyze possible cavitation fluid-dynamic instabilities both optically and by means of pressure fluctuation analysis. Fourier analysis showed the occurrence of a cavity length oscillation at a frequency of 14.7Hz, which corresponds to the frequency of the rotating stall instability detected by means of pressure oscillation analysis.

The present paper illustrates the set-up and the preliminary results of an experimental investigation of cavitation flow instabilities carried out by means of a high-speed camera on a three bladed inducer in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Alta S.p.A. The brightness thresholding technique adopted for cavitation recognition is described. A semi-automatic binary algorithm has been used for processing high speed videos of the cavitating inducer. In order to test the capabilities of the algorithm, the mean frontal cavitating area has been computed under different operating conditions. The tip cavity length has also been evaluated as a function of time. Fourier analysis showed the occurrence of a cavity length oscillation at a frequency of 15.7 Hz, which corresponds to the frequency of the rotating stall instability previously detected on the same inducer by means of pressure oscillations analysis.

In the framework of the PulCheR project, an experimental test campaign on a 40 N bipropellant thruster prototype has been carried out with the aim of assessing the attainable propulsive performance in steady state conditions of 98% concentration hydrogen peroxide and propyne. The experimental specific impulse measured at sea level with the matched conical nozzle of the prototype has been 213 s that corresponds to an extrapolated vacuum specific impulse for a high expansion area ratio bell-contoured nozzle higher than 320 s. The light unsaturated hydrocarbon has been effectively ignited by the oxygen-rich hot gases produced by the catalytic decomposition of the hydrogen peroxide.