SVILUPPO DI UN MODELLO PER LA PROGETTAZIONE DI TURBOPOMPE CENTRIFUGHE

Nel campo dei sistemi propulsivi spaziali, lo studio delle turbopompe a liquido rappresenta uno dei campi di maggior interesse. Utilizzate nella totalità dei lanciatori spaziali, le turbopompe permettono di ridurre la pressione di immagazzinamento dei propellenti nei serbatoi e garantiscono un’elevata pressione in camera di combustione. La presenza di questi organi permette, quindi, una riduzione sostanziale dei pesi e un aumento della spinta generata. In quest’ottica, ogni piccolo guadagno in termini di efficienza per questo tipo di turbomacchine ha un notevole impatto economico. Una buona comprensione del comportamento del flusso all’interno delle turbopompe è estremamente complessa. Per questo la progettazione di tali componenti è effettuata attraverso particolari schemi di tipo iterativo la cui risoluzione richiede una cura particolare e tempi di calcolo considerevoli. La presente tesi consiste nello sviluppo modello teorico 3D in grado di predire rapidamente geometria e prestazioni di turbopompe in modo tale da fornire utili indicazioni per la progettazione preliminare della macchina. Dopo una piccola introduzione sulle turbomacchine, nel capitolo 2 si descrivono le principali caratteristiche geometriche e operative delle turbopompe, ponendo particolare attenzione ai singoli elementi che ne compongono la struttura principale: la girante, il diffusore e la voluta. Nel capitolo 3 si espone dettagliatamente il modello in condizioni ideali: privo dei fenomeni di perdita caratteristici di questo tipo di macchina. Sotto le ipotesi di flusso incomprimibile, non viscoso, sono illustrate e descritte le equazioni che permettono di disegnare gli elementi principali della turbopompa e di caratterizzarne il flusso all’interno. Il capitolo 4 si concentra sull’analisi dei fenomeni di perdita trascurati nel capitolo precedente per ciascuno dei componenti della macchina. Si pone particolare attenzione su una possibile formulazione e risoluzione delle equazioni che governano gli strati limite all’interno della girante e sulle perdite connesse con il loro sviluppo. Le altre perdite analizzate riguardano essenzialmente la variazione della direzione del flusso, il mescolamento turbolento e la presenza di fenomeni di diffusione. Nel capitolo 5 si sviluppa un criterio per la progettazione di una pompa ottimale per un dato impiego. Si individuano in tale metodo: i parametri geometrici e operativi richiesti in fase preliminare di progettazione, i parametri geometrici per l’ottimizzazione e le funzioni obiettivo. Nella parte finale si presentano alcuni esempi di geometrie ottimizzate. Infine, nell’ultimo capitolo (capitolo 6) si presentano alcuni possibili sviluppi dell’attività. L’intero lavoro è stato compiuto presso ALTA S.p.A. con la collaborazione e supervisione del Prof. Luca d’Agostino e del Dott. Ing. Angelo Pasini. In space rocket propulsion , liquid feed turbopumps represent one of the most interesting fields of study and development. Current rocket propellant feed turbopumps are used in order to reduce the propellant tank pressure and weight and to improve combustion chamber pressure. Therefore any small gain in their efficiency and performance translates into major economic impacts. A full comprehension of the flow-field inside a turbopump is extremely complex. Typical iterative schemes for the design of blading and flow path in centrifugal machines have to be applied carefully and require considerable computational power. The present thesis is concerned with the development of 3D theoretical model capable of rapidly predicting the geometry and performance of radial impellers in order to provide indications for the preliminary design of the machine. After a brief introduction about the turbomachines, in chapter 2 the main geometrical and operational features of turbopumps are showed with particular attention to the elements that set up the structure: the impeller, the diffuser and the volute. In chapter 3, the model is exposed under ideal conditions: without any of the typical loss phenomena of this kind of turbomachines. Under the assumptions of incompressible, non-viscous flow all the relevant equations are carried out in order to design the main elements of the turbopump and in order to describe the flow-field inside. Chapter 4 is focused on the analysis of loss mechanisms for each element of the turbopump. In particular, a formulation and a resolution of the boundary-layer-growth problem is showed. Other contributions to the losses arise from flow incidence at the blade leading edge, from turbulent mixing and diffusion. In chapter 5 the optimal turbopump design issue is illustrated. An optimization code from the model discussed in the above chapters is carried out. Geometrical and operational requirements for preliminary design are identified and an objective-function is defined. Finally, the last chapter (chapter 6) illustrates and discusses some possible developments of the present work. The thesis work has been carried out at Alta S.p.A. research laboratory, under the supervision of Prof. Luca d’Agostino and Doc. Eng. Angelo Pasini

Additive Manufacturing of Poly(Methyl Methacrylate) Biomedical Implants with Dual-Scale Porosity

The development of bone permanent implants with a porous structure favoring their integration with the surrounding tissues is emerging as an attractive field of application of additive manufacturing (AM). This article reports on the investigation of the suitability of a hybrid AM technique, that is, computer-aided wet-spinning (CAWS), to fabricate novel poly(methyl meth- acrylate) (PMMA) constructs as porous implant prototypes. The optimization of the processing parameters to fabricate PMMA samples with a predefined internal porous structure and different external shapes is described. The study demonstrates that tailoring post-processing conditions represents a powerful tool to optimize samples macroscopic aspect, micromorphology, and mechanical properties. In particular, the possibility of obtaining a dual-scale porosity through the integration of the macroporous structure determined by the material lay-down pattern with a submicrometric porosity resulting from the phase inversion process governing polymer solidification, together with the possibility of purifying the employed commercial material from residual monomer during coagulation in ethanol, are reported as note- worthy advantages of CAWS over other AM techniques. A natural progression of this work is the development of relevant complex anatomical prototypes with tailored porosity by processing digital data obtained from computer tomography imaging of bone defects

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

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

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

Fourth generation head fracture in ceramic-on-polyethylene bearing after hip revision surgery: a case report

Fourth generation ceramic bearings (BIOLOX delta, CeramTec AG; Phlochingen, Germany) were developed to reduce wear debris and improve fracture resistance. A case of a fourth generation head fracture in ceramic-on-polyethylene (COP) coupling after hip revision surgery is reported. A 58-year-old man was admitted to our department for increasing hip pain following a direct trauma which occurred during skiing activity 4 months before. Six years earlier, he had undergone a right cementless revision surgery with a 36-mm BIOLOX delta femoral head on polyethylene liner for metallosis and foreign body reaction after primary total hip replacement for hip osteoarthritis. At admission, radiological evaluation revealed a fracture of ceramic femoral head requiring a new revision surgery. Extensive synovectomy, lavage and capsulectomy were performed. Both acetabular cup and femoral stem were well fixed with no damage of trunnion, and therefore they were retained. A 36-mm internal diameter polyethylene acetabular liner was inserted along a 36-mm BIOLOX delta head with a BioBall adapter XL. The postoperative course was uncomplicated. At 1-year follow-up, the patient had a complete functional recovery. To our knowledge, BIOLOX delta ceramic femoral head fracture after COP hip revision surgery has not been previously reported

PULCHER – Pulsed Chemical Rocket with Green High Performance Propellants: Project Overview

PulCheR is a research project co-funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n°313271, officially started as of January 1st, 2013. The project 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 suitable design of the feeding lines, comprehensive of the injectors, allows the low pressure injection of the correct amount of propellants into the combustion chamber: the decomposition or combustion reaction increase the chamber pressure that rises to values much higher than the one at which the propellants are stored, exploiting the advantages of quasi constant volume combustion. The combustion products are accelerated through a convergent-divergent nozzle generating the thrust pulse and once the pressure inside the combustion chamber decreases under the injection pressure, the cycle can be repeated. The feasibility of this new propulsion concept will be investigated at breadboard level in both mono and bipropellant configurations through the design, realization and testing of a platform of the overall propulsion system including all its main components. In addition, the concept will be investigated using green propellants with potential similar performance to the current state-of-the-art for monopropellant and bipropellant thrusters. The present paper aims at presenting the main objectives and the current status of the PulCheR project

Discrimination of tropical forest types, dominant species, and mapping of functional guilds by hyperspectral and simulated multispectral Sentinel-2 data

To answer new scientific and ecological questions and monitor multiple forest changes, a fine scale characterization of these ecosystems is needed, and could imply the mapping of specific species, of detailed forest types, and of functional composition. This characterization can be now provided by the novel Earth Observation tools. This study aims to contribute to understanding the innovation in forest and ecological research that can be brought in by advanced remote sensing instruments, and proposes the guild mapping approach as a tool to efficiently monitor the varied tropical forest resources. We evaluated, in tropical Ghanaian forests, the ability of airborne hyperspectral and simulated multispectral Sentinel-2 data, and derived vegetation indices and textures, to: distinguish between two different forest types; to discriminate among selected dominant species; and to separate trees species grouped according to their functional guilds: Pioneer, Non Pioneer Light Demanding, and Shade Bearer. We then produced guild classification maps for each area using hyperspectral data. Our results showed that with both hyperspectral and simulated Sentinel-2 data these discrimination tasks can be successfully accomplished. Results also stressed the importance of texture features, especially if using the lower spectral and spatial Sentinel-2 resolution data, and highlighted the important role of the new Sentinel-2 data for ecological monitoring. Classification results showed a statistically significant improvement in overall accuracy using Support Vector Machine, over Maximum Likelihood approach. We proposed the functional guilds mapping as an innovative approach to: (i) monitor compositional changes, especially with respect to the effects of global climate change on forests, and particularly in the tropical biome where the occurrence of hundreds of species prevents mapping activities at species level; (ii) support large-scale forest inventories. The imminent Sentinel-2 data could serve to open the road for the development of new concepts and methods in forestry and ecological research

The promises of large language models for protein design and modeling.

The recent breakthroughs of Large Language Models (LLMs) in the context of natural language processing have opened the way to significant advances in protein research. Indeed, the relationships between human natural language and the language of proteins invite the application and adaptation of LLMs to protein modelling and design. Considering the impressive results of GPT-4 and other recently developed LLMs in processing, generating and translating human languages, we anticipate analogous results with the language of proteins. Indeed, protein language models have been already trained to accurately predict protein properties, generate novel functionally characterized proteins, achieving state-of-the-art results. In this paper we discuss the promises and the open challenges raised by this novel and exciting research area, and we propose our perspective on how LLMs will affect protein modeling and design