A Simplified Analytical Model for Evaluating the Noncavitating Performance of Axial Inducers

The present paper describes an analytical model for the preliminary prediction of the noncavitating flow field and performance of helical inducers. The proposed model is based on the traditional troughflow theory approximations with empirical corrections for outlet flow deviation and hydraulic losses due to inlet incidence effects and friction in the blade channels. Unlike most classical models, it allows – even if under still rather restrictive assumptions – for the prediction of the radial and circumferential flow velocity fields at the inducer exit section and for the approximate evaluation of the head coefficient as a function of the flow coefficient in terms of the static pressure rise generated by the inducer. The results are presented of the model validation by comparison with the experimental data obtained for several inducers tested in different facilities worldwide

Assessment of the Propulsive Performance of Fuel Vapor Pressurized Hydrogen Peroxide-Ethane Rocket Engines

In the last years low-toxicity “green” storable liquid propellants have become considerably more attractive as possible substitutes for nitrogen oxides and hydrazines. The main advantage of “green” propellants is represented by the significant cost savings associated with the drastic simplification of the health and safety protection procedures necessary during propellant production, storage and handling. Fuel Vapor Pressurization (FVP) technology of “green” bipropellant rocket engines potentially offers very significant additional advantages in terms of system cost, complexity, reliability, safety and mass, with practically no penalty in propulsive performance compared to traditional storable propellants such as mixed nitrogen oxides and hydrazines. Pioneering FVP experiments were carried out by Goddard, Wyld and others. Detailed studies have been conducted and several tests have been successfully performed since 1994 in the US, but no such experience is presently available in Europe, nor FVP has ever attained flight readiness anywhere in the world. The main characteristics of the FVP system examined in this work consist in the use of storable, non-toxic, inexpensive, non hypergolic, high-energy propellants such as hydrogen peroxide (HP, H2O2) and ethane (C2H6) and in the storage of these propellants in a single lightweight tank, using a flexible diaphragm or a bladder to separate the fuel from the oxidizer and a catalytic reactor to decompose the hydrogen peroxide before mixing and combustion with ethane. This configuration therefore yields a very simple and yet highly efficient and reliable propulsion system by eliminating the cost, the weight and complexity of propellant tanks and pressurization bottles, pressure and flow regulators and ignition systems. These advantages are of special relevance in low- or mediumthrust rocket engines for the rapidly expanding market of “small” space missions and led the authors to focus on the analysis and assessment of propulsion systems operating according to this concept. The present paper reports therefore the preliminary evaluation of fuel vapor pressurized H2O2-C2H6 rocket propulsion systems. The results of the analysis confirm that the development of FVP technology may represent a significant contribution to the containment of the propulsion cost of small- and medium-size spacecrafts

A New Cavitation Test Facility at Centrospazio

The present paper illustrates the result of the trade-offs between operational requirements and practical limitations leading the final design of the CPTF (Cavitating Pump Test Facility), the CPRTF (Cavitating Pump Rotordynamic Test Facility) and the related TCT (Thermal Cavitation Tunnel). The CPTF is an experimental apparatus specifically designed for the performance analysis of turbopumps in fluid dynamic and inertial/thermal cavitation similarity conditions. The apparatus, operating in water up to 90°C, is capable of controlling the pump’s operational conditions and carrying out the measurement of the steady and/or unsteady flow parameters (pressure, velocity, temperature) at the inlet and discharge of full-scale cavitating/noncavitating turbopumps for space propulsion applications. More generally, the CPTF is designed as a flexible, versatile and inexpensive facility that can be readily be adapted to carry out detailed experimental investigations on practically any kind of fluid dynamic phenomena relevant to high performance turbopumps. The CPRTF is currently being completed under ASI (Agenzia Spaziale Italiana) funding and consists in an upgraded version of the CPTF capable of carrying out the measurement of the steady and unsteady rotodynamic forces exerted by the flow on whirling impellers of cavitating/noncavitating turbopumps using an especially designed rotating dynamometer. To this purpose the CPRTF can operate the pump under forced whirl conditions on a circular orbit with assigned eccentricity and angular speed. The TCT is a small-scale water tunnel that can be installed on the suction line of the CPTF, with the specific capability of running tests under thermal cavitation similarity conditions. The main operational requirements and development choices that led to the final configurations of the CPTF, CPRTF and TCT are illustrated and their performance in testing cavitating/noncavitating turbopumps and hydrofoils under fluid dynamic and thermal cavitation similarity are illustrated. Experimental results are presented to document the present capabilities of the facility in a number of typical configurations and operational conditions

Experimental Activities on Liquid Propellant Turbopumps at Centrospazio

The present paper reviews recent experimental activities at Centrospazio on cavitation in liquid propellant turbopumps. These activities have been carried out in a dedicated, low-cost, versatile and easily instrumentable test facility, designed in 1996 under ESA (European Space Agency) funding and later refined and realized in 1999-2000 under a 1998/99 Fundamental Research contract by ASI (Italian Space Agency). The first part of the paper describes the characteristics and performance of the three alternative configurations of the facility: the CPTF (Cavitating Pump Test Facility), for general experimentation on cavitating/non-cavitating turbopumps under fluid dynamic and thermal cavitation similarity; the CPRTF (Cavitating Pump Rotordynamic Test Facility), capable of investigating rotordynamic fluid forces under forced vibration experiments on turbopump rotors of adjustable eccentricity and sub-synchronous or super-synchronous whirl speeds; and the TCT (Thermal Cavitation Tunnel), specifically designed for the investigation of 2D or 3D cavitating flows over test bodies in thermal cavitation similarity conditions. The second part of the paper presents some recent results of cavitation tests on helical inducers and hydrofoils. Future activities in this field at Centrospazio are illustrated

Cavitation Experiments on Turbopump Inducers and Hydrofoils at Alta/Centrospazio: Overview and Future Activities

The aim of the present paper is to provide some highlights about the most interesting experimental activities carried out during the years 2000-2004 through the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio/Alta S.p.A. After a brief description of the facility, the experimental activities carried out on a NACA 0015 hydrofoil for the characterization of the pressure coefficient on the suction side and evaluation the cavity length and oscillations are presented. Then, the results obtained to characterize the performance and the cavitation instabilities on three different axial inducers are showed: in particular, a commercial three-bladed inducer, the four-bladed inducer installed in the LOX turbopump of the Ariane Vulcain MK1 rocket engine and the “FAST2”, a twobladed one manufactured by Avio S.p.A. using the criteria followed for the VINCI180 LOX inducer. The ..

Thermal Cavitation Experiments on a NACA 0015 Hydrofoil

The present paper illustrates the main results of an experimental campaign conducted in the Thermal Cavitation Tunnel of the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio. Experiments were carried out on a NACA 0015 hydrofoil at various incidence angles, cavitation numbers and freestream temperatures, in order to investigate the characteristics of cavitation instabilities and the impact of thermal cavitation effects. Measured cavity length, surface pressure coefficients and unsteady pressure spectra are in good agreement with the data available in the open literature and suggest the existence of a strong correlation between the onset of the various forms of cavitation and instabilities, the thermal cavitation effects, and the effects induced by the presence of the walls of the tunnel. Further analytical investigations will be carried out in order to provide a better interpretation of the above results

Metagenomic analysis of dental calculus in ancient Egyptian baboons

Dental calculus, or mineralized plaque, represents a record of ancient biomolecules and food residues. Recently, ancient metagenomics made it possible to unlock the wealth of microbial and dietary information of dental calculus to reconstruct oral microbiomes and lifestyle of humans from the past. Although most studies have so far focused on ancient humans, dental calculus is known to form in a wide range of animals, potentially informing on how human-animal interactions changed the animals' oral ecology. Here, we characterise the oral microbiome of six ancient Egyptian baboons held in captivity during the late Pharaonic era (9th-6th centuries BC) and of two historical baboons from a zoo via shotgun metagenomics. We demonstrate that these captive baboons possessed a distinctive oral microbiome when compared to ancient and modern humans, Neanderthals and a wild chimpanzee. These results may reflect the omnivorous dietary behaviour of baboons, even though health, food provisioning and other factors associated with human management, may have changed the baboons' oral microbiome. We anticipate our study to be a starting point for more extensive studies on ancient animal oral microbiomes to examine the extent to which domestication and human management in the past affected the diet, health and lifestyle of target animals

Oral health-related quality of life in partially edentulous patients before and after implant therapy: a 2-year longitudinal study

The aim of this study was to measure the Oral Health-Related Quality of Life (OHRQoL) before and after a prosthodontic implant therapy so to determine the physical and psychological impact of implant-supported fixed partial dentures (IFPD) rehabilitation among edentulous patients. Methods. 50 partially edentulous patients aged 40-70 years, treated with IFPD, completed the OHRQoL questionnaire before the implant surgery (Time 0) and 2 years after their whole implant-prosthetic rehabilitation (Time 1). The questionnaire was proposed in a short version of Oral Health Impact Profile (OHIP-14, range 0-56) and analyzed through the ‘additive method’. We evaluated statistical mean, standard deviation, median, variance and mode of all OHIP-14 domains and the statistical significance about oral changes at Time 0 and Time 1 using the Chi-square test (p-values 0.05). Patients with I and IV Kennedy’s class edentulism showed better improvement (p < 0.05). Preoperative and post-treatment assessments of OHRQoL exhibited significant differences. The IFPD treatment had a positive effect on the OHRQoL, which improved better in patients with I and IV Kennedy’s edentulous class

Experimental Characterization of the Cavitation Instabilities in the Avio “FAST2” Inducer

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 FAST2 inducer, a two-bladed axial pump designed and manufactured by Avio S.p.A. 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 a given 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 having a frequency of about 4.4W and a rotating stall at about 0.31W. Some experiments were carried out under forced vibration cond..

Atomic force microscopy of bacteria from periodontal subgingival biofilm: Preliminary study results

OBJECTIVE: Atomic force microscope (AFM) is a technology that allows analysis of the nanoscale morphology of bacteria within biofilm and provides details that may be better useful for understanding the role of bacterial interactions in the periodontal disease. MATERIAL AND METHODS: Five patients with periodontal ≥5 mm pockets diagnosed as generalized periodontitis and five patients with slight gingivitis were selected for the investigation. Bacteria biofilms were collected and morphologically investigated by AFM application. RESULTS: The investigation revealed how periodontitis bacteria are characterized by specific morphologic features of the cell wall. The major representative species of bacteria causing periodontal diseases have been reproduced by a three-dimensional reconstruction showing the bacteria surface details. CONCLUSIONS: The presence of complex glycocalyx structures, bacteriophage-like vesicles, spirochetes (classic and cystic morphology) and bacterial co-aggregation has been identified by the AFM analysis. The results suggest that AFM is a reliable technique for studying bacterial morphology and for examining microbial interactions in dental plaque