PROGETTAZIONE E REALIZZAZIONE DI UN IMPIANTO DI PROVA PER ENDOREATTORI A PEROSSIDO DI IDROGENO

Il perossido di idrogeno è un propellente “verde”, non tossico caratterizzato da notevoli semplificazioni nella sua gestione rispetto agli altri propellenti spaziali, per quanto riguarda la produzione, lo stoccaggio e la manipolazione. Razzi monopropellenti a perossido di idrogeno sono soluzioni interessanti per motori con spinte medie o basse. In questa tesi si è sviluppato un impianto per testare motori monopropellenti a H2O2 che permette di misurare le prestazioni degli endoreattori e di caratterizzare i principali elementi che li costituiscono, in particolare il catalizzatore, dove avviene la reazione di decomposizione esotermica della molecola

Pumping Performance Similarity, Cavitation-Induced Instabilities and Fluid-Induced Rotordynamic Forces in Tapered Inducers

A comprehensive experimental campaign has been carried out on two highhead, mixed-flow unshrouded inducers with tapered-hub and variable-pitch. Both the pumps, called DAPAMITO inducers, have been designed by means of a reduced order model and procedure reported in this thesis. The model is based on the incompressible, inviscid, irrotational flow approximation, where the 3D velocity field inside the blade channels is expressed as the superposition of a fully-guided axisymmetric flow with radially uniform axial velocity and a 2D cross-sectional vorticity correction. Boundary layer blockage is estimated by means of a suitable redefinition of the diffusion factor for bladings with non-negligible radial flow and Carter's rule is used to account for flow deviation at the inducer trailing edge. Performance losses are evaluated by adding suitably adapted correlations of turbulent duct losses to the inlet flow incidence losses. The noncavitating performance of the inducers has been investigated at different clearance and temperature. The close matching between the experimental data in cold water and the predicted performance has confirmed both the predictive capability of the reduced order model and the high-head nature of the DAPAMITO inducers. The suction performance of the inducers have been investigated at design and off-design conditions both at high and low clearance in cold and hot water. Several cavitation-induced instabilities has been detected and identified on the DAPAMITO inducers. The experimental evidence suggests that the occurrence of the synchronous rotating cavitation can be associated to a strong performance degradation. Furthermore, the comparison between the results at low and high clearance clearly highlights that a high value of the clearance tends to suppress the rotating instabilities, whereas it seems that axial phenomena are not affected, or at least less affected, by the tip blade clearance. 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. A new typology of cavitation thermal effects has been identified in the influence of the temperature on the intensity of the performance degradation associated to the attached cavitation instability. 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 to this type of instability. The tests carried out on whirling inducers has investigated the roles of the flow coefficient, cavitation number, liquid temperature and of the imposed whirl motion of the rotor. The spectra, especially the continuous ones obtained by means of a novel data reduction procedure, of the rotordynamic forces measured at several flow coefficients in noncavitating regime clearly show the same qualitative behavior for both the inducers. The occurrence of large destabilizing peaks confirms that the conventional approach which uses the stiffness, damping and inertia matrices is clearly not able to characterize rotordynamic forces on noncavitating/cavitating inducers. For positive whirl frequency ratio, the continuous spectra of the module of the rotordynamic force clearly show a minimum that corresponds to a negligible intensity of the force and a maximum associated to the beginning of a destabilizing range. The intensity of the flow reversal and the magnitude of rotation in the tip clearance flow and backflow affect the strength of the rotordynamic force and the location of the minimum and maximum with respect to the whirl frequency ratio. The experimental results have confirmed that the cavitation has a dramatically clear destabilizing effect on the rotordynamic forces. Under cavitating regime, the minimum usually happens at the same value of the whirl ratio of noncavitating condition while, in general, the maximum is anticipated and its intensity is higher. For negative whirl ratio, the cavitation tends to reduce the stabilizing range to a small interval next to zero. Based on the available experimental evidence, the novel data reduction procedure capable of obtain a continuous spectrum of fluid-induced rotordynamic forces can be very useful to catch the unlikely foreseeable complexity of the rotordynamic forces and their consequences on stability of axial flow inducers. Finally, a brief overview of the laws of similarity in pumps has been provided. The second part of the thesis reports the results of a further research activity carried out during the years of the Ph. D. course. The research deals with a comprehensive experimental campaign on three hydrogen peroxide monopropellant thruster prototypes performed in order to characterize the decomposition capabilities of seven different platinum catalysts on alumina carriers for the decomposition of high grade hydrogen peroxide

MODELLING OF DEPLOYABLE CABLE NETS FOR ACTIVE SPACE DEBRIS REMOVAL

Space debris represent a true risk for current and future activities in the circumterrestrial space, and remediation activities must be set out to guarantee the access to space in the future. For active debris removal, the development of an effective capturing mechanism remains an open issue. Among several proposals, cable nets are light, easily packable, scalable, and versatile. Nonetheless, guidance, navigation, and control aspects are especially critical in both the capture and post-capture phases. We present a finite element model of a deployable cable net. We consider a lumped mass/cable net system taking into account non-linearities arising both from large displacements and deformations, and from the different response of cables when subject to tension and compression. The problem is stated by using the nodal coordinates as Lagrangian coordinates. Lastly, the nonlinear governing equations of the system are obtained in a form ready for numerical integration

On the Preliminary Design and Performance Prediction of Centrifugal Turbopumps—Part 2

The ideal flow model for the preliminary design and performance prediction of radial turbopumps presented in the companion paper of the present volume (d’Agostino et al., 2017) is here interfaced with the calculation of the boundary layers inside the blade channels and other major forms of flow losses, with the aim of developing an effective tool for rapid parametric optimization of the machine performance and geometry under appropriate design constraints, such as assigned values of the specific speed, flow coefficient and blade solidity. A mixed-flow turbopump, with a six-bladed impeller, a vaneless diffuser, a single-spiral volute and nondimensional performance characteristics similar to those typically used in liquid propellant rocket engine feed systems, has been designed, parametrically optimized and manufactured in accordance with the indications of the present model. The pumping and suction performance of the machine have been determined in a series of tests in the Cavitating Pump Rotordynamic Test Facility (CPRTF). Under fully-wetted flow conditions the measured pumping characteristics of the machine (hydraulic head and efficiency as functions of the flow coefficient) proved to be in excellent agreement with the model predictions, thus successfully confirming the validity of the proposed model as an effective tool for rapid and efficient design of high-performance centrifugal turbopumps

A Reduced Order Model for Optimal Centrifugal Pump Design

A reduced order model for preliminary design and noncavitating performance prediction of radial turbopumps has been illustrated in a previous paper presented by the same authors. The model expresses the 3D incompressible, inviscid, irrotational flow through helical blades with slow axial variations of the pitch and backsweep by superposing a 2D cross-sectional axial vorticity correction to a fully-guided flow with axisymmetric stagnation velocity in the meridional plane. Application of the relevant governing equations yields a set of constraints for the axial evolution of the blade pitch and backsweep that allows for the closed form definition of the impeller geometry and flowfield in terms of a reduced number of controlling parameters. In turn, mass and momentum conservation are used to account for the mixing of the flow leaving the impeller and its coupling with 2D reduced order models of the flow in the diffuser (if any) and the volute, thus generating the information necessary for completing the geometric definition of the machine and for determining its ideal noncavitating performance in accordance with the resulting flowfield. In the present paper, the above ideal flow model has been interfaced with the calculation of boundary layers inside the blade channels and other major forms of flow losses, with the aim of developing an effective tool for rapid parametric optimization of the machine geometry and performance under appropriate design constraints such as target values of the specific speed, flow coefficient and impeller blading solidity

Experimental Performance of a Tapered Axial Inducer: Comparison with Analytical Predictions

The present paper illustrates the results of an experimental campaign conducted in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Alta S.p.A. for the characterization of the pumping and suction performance of a three-bladed, tapered-hub, variable-pitch inducer, indicated as DAPAMITO3. The test inducer has been sized and designed by means of the reduced order model recently developed at Alta S.p.A. for the definition of the geometry and the prediction of the non-cavitating performance of typical high-head space rocket inducers. The pumping performance of the inducer proved to be in good accordance with the model predictions. The effects of the blade tip clearance have been investigated and the corresponding performance degradation has been correctly predicted by means of a semi-empirical extension of the model. Finally, the effects of the working fluid temperature on both the non-cavitating and cavitating performance of the inducer have been analysed. At higher ..

Cavitation and Flow Instabilities in a 3- Bladed Axial Inducer Designed by Means of a Reduced Order Analytical Model

The present paper illustrates the main results of an experimental campaign conducted using the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Alta S.p.A. The tests were carried out on the DAPAMITO inducer, a three-bladed axial pump designed and manufactured by Alta S.p.A. using a simplified analytical model for the prediction of geometry and noncavitating performance of typical space rocket inducers. The transparent inlet section of the facility was instrumented with several piezoelectric pressure transducers located at three axial stations: inducer inlet, outlet and the middle of the axial chord of the blades. At each axial station at least two transducers were mounted with given angular spacing in order to cross-correlate their signals for amplitude, phase and coherence analysis. However, probably because of the high value of the blade tip clearance, very few flow instabilities have been detected on the inducer, including: steady asymmetric cavitation caused by the different extension of the cavitating regions on the blades; cavitation surge at a frequency equal to 0.16 times the inducer rotational frequency; a higher-order axial phenomenon at 7.2 times the rotational frequency

Rotordynamic Forces on a Three Bladed Inducer under Forced Whirl Motion Operating at Different Conditions

The paper illustrates the main 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 three-bladed, tapered-hub, variable-pitch inducer, named DAPROT3. 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 results have been obtained by means of a recent experimental technique, consisting in measuring the continuous spectra of the rotordynamic forces as functions of the whirl excitation frequency. This technique allows for extrapolating valuable information from the experiments by more accurately and rapidly characterizing the spectral behavior of these forces than can be obtained from a limited number of point experiments conducted at constant whirl frequency. Therefore, it is useful to better capture the complexity of the rotordynamic forces and assess their consequences on the stability of axial inducers

Cavitating Pump Rotordynamic Test Facility at ALTA S.p.A.: Upgraded Capabilities of a Unique Test Rig

The paper illustrates the upgrades recently introduced in Alta’s Cavitating Pump Rotordynamic Test Facility in order to extend its experimental capabilities, with special reference to the addition of an auxiliary pump for testing of turbopump inducers over a wider range of flow coefficients, and the set-up of an original apparatus specifically designed for the characterization of the dynamic transfer matrices of cavitating inducers and turbopumps. Examples are presented of the improved capabilities of the facility