Paolo Casoli

Modelling of fluid properties in hydraulic positive displacement machines

Abstract This paper presents a numerical model for the simulation of a swash-plate axial piston pump, focusing on the characterization of fluid properties. As it is well known, the reduction of flow oscillations (which generates pressure ripples and produces vibration and noise in the entire circuit) and the avoidance of cavitation are the major problems in the design of these pumps. Developing a simulation code can be very useful for component optimisation in order to predict and reduce the undesired phenomena. The paper first gives a quick overview on a previously developed pump model; afterwards four different models of the fluid are presented: they take into account cavitation in different ways. Their aim at characterizing as well as possible the unsteady and erratic cavitation features in a simplified manner, in order to apply the models to the simulation of hydraulic components. In the second part of the paper an application is shown of these models to an axial piston pump: a few results are presented and compared with available test data. The effects of the fluid models on the predicted pump performance are shown and commented.

A novel approach for predicting the operation of external gear pumps under cavitating conditions

Abstract This paper addresses the problem of predicting the effects of gas cavitation in fluid power components, accounting for the dynamic features of gas (including free air and vapour) release and adsorption. Several approaches to evaluate fluid properties under cavitating conditions have been proposed in the past, but those suitable to model hydraulic components with the classic lumped parameter approach do not consider the dynamic nature of the gas cavitation process. Cavitation can have a relevant impact on component operation, particularly for positive displacement machines directly connected to the oil reservoir. With the goal of studying the cavitation effects in hydrostatic units, in this paper a novel model to describe fluid properties – which utilizes a simplified formulation of the Full Cavitation Model – was integrated in an existing lumped parameter model for external gear machines previously developed by the authors’ research team. While the basic formulation of the new fluid model was previously validated for a single closed fluid chamber, the present study extends its formulation for the case of complete systems in which multiple chambers with variable volume are connected to each other. A proper experimental set-up was developed to permit the validation of the proposed model for the case of external gear pumps. Comparisons between measured and simulated instantaneous internal tooth space pressures as well as the outlet flow rates are presented. The significance of the proposed model is highlighted by comparing its predictions with those obtained using classic models of fluid properties, which cannot predict with accuracy the effects of cavitation.

A numerical procedure for predicting the performance of high pressure homogenizing valves

Abstract This paper describes a numerical procedure for the prediction of the homogenizing performance of high pressure homogenizing valves used in diary plants . The method is based on a strict interaction between a complex CFD code and a simple homogenizing simulation code developed by the authors. This latter implements a mathematical model for the evaluation of droplets break-up, that needs an accurate evaluation of few significant fluid dynamic parameters in the whole fluid dynamic domain inside the valve. Due to the relevant pressure gradients within the flow and to the possibility of cavitation, particular attention has been paid in defining the fluid model, the mesh and the parameters required for CFD simulations. Notwithstanding the quite simple model of the homogenizing process, comparatively with the complexity of phenomena involved, the first results obtained are in general agreement with the experimental data available. These results point out the potential of the procedure proposed as a starting point for further implementation of more complex effects.

On the Analysis of Experimental Data for External Gear Machines and Their Comparison With Simulation Results

This paper deals with the simulation of hydraulic gear machines, focusing on the validation of simulation models and on the comparison between numerical results and experimental data, concerning both steady and unsteady conditions. First authors give a brief overview on the simulation tool HYGESim, which has been presented and discussed in several previous papers. Afterwards, the attention shifts on the analysis of the simulation results for the case of a stock gear pump. Regarding steady state characteristics, the paper shows how HYGESim is able to accurately reproduce the operation of the analyzed pump, in terms of flow, pressures and efficiency maps. Regarding unsteady simulations, namely the delivery pressure ripple, the paper highlights the significant effort done by the authors in order to achieve experimental data clear and suitable for the comparison with simulation results. In fact, the peculiarities of common measuring systems (in particular of the load apparatus and the sampling methods) are often difficult to reproduce numerically: frequently different acceptable assumptions in the numerical model lead to remarkable discrepancies in simulated results. For this purpose, the authors developed a measuring device mainly focused on the easy reproducibility in the simulation environment. Furthermore, an original technique for processing unsteady data (pressure and flow ripples) is proposed, allowing to achieve comparable data indifferently of the adopted sampling method and of the data origin (experimental or numerical). In the final part of the paper, pressure ripple simulations and test results (obtained with the described measuring system and analyzed with the described technique) are presented and compared.Copyright

Optimization of Injection Law for Direct Injection Diesel Engine

This paper describes how different timing and shape of the injection law can influence pollutant emission of a direct injection diesel engine. The study was carried out making use of a multizone thermodynamic model as regards the closed valve phase, and a filling-emptying one as regards the open valve phase. After being calibrated by comparison with experimental data, the abovementioned model was used for injection law optimization as regards minimum pollutant concentration (NO[sub x] and soot) in the exhaust gases with the smallest engine performance reduction possible.

Mathematical Model of a Hydraulic Excavator for Fuel Consumption Predictions

This paper presents the multibody mathematical model of a hydraulic excavator, developed in the AMESim® environment, which is able to predict the machinery fuel consumption during the working cycles. The mathematical modelling approach is presented as well as the subsystems models. The experimental activity on the excavator is presented in detail. The excavator fuel consumption was measured according to the JCMAS standard. The working cycles were executed an appropriate number of times in order to minimize the stochastic influence of the operator on the fuel consumption. The results show the mathematical model capability in the machine fuel consumption prediction. The excavator model could be useful either to perform accurate analyses on the energy dissipation in the system, giving the possibility to introduce new system configurations and compare their performance with the standard one, or for the definition of novel system control strategies in order to achieve the fuel consumption reduction target.Copyright

A LEARNING-MACHINE BASED METHOD FOR THE SIMULATION OF COMBUSTION PROCESS IN AUTOMOTIVE I.C. ENGINES

In automotive applications problems related to management and diagnostics play an important role to improve engine performance and to reduce fuel consumption and pollutant emissions. In the design of control systems the use of theoretical models for the simulation of engine behaviour proved to be very useful, and it is apparent from the literature. However, since automotive engines have become very complex plants, their modelling requires a comprehensive description of the behaviour of many processes and components. Combustion process has a strong influence on performance and emissions, but its theoretical description can be hardly combined with the requirements of control-oriented models (especially as regards “real-time” applications). Two simplified theoretical models are proposed in the paper, based on a thermodynamic and a simplified approach respectively. In the first case a single-zone method was followed with the introduction of an apparent heat release rate (HRR) described as a superposition of two Wiebe functions. Coefficients of these burning functions are estimated by means of Learning Machines (LM), i.e. Support Vector Machines (SVM), trained from experimental data and then embedded in a Simulink® block. In order to make calculation time shorter, a simpler and faster model based on the application of SVM was defined to describe combustion process. Starting from experimental data, the proposed SVM was trained and implemented in a Simulink® block to evaluate exhaust gas temperature and bmep directly from engine operating parameters. Both blocks were defined to be easily embedded in engine simulation models for control-oriented applications. Results were promising for both models, showing very short computation time. A comparison of theoretical outputs with experimental data is reported in the paper, together with an application of both calculation procedures to a comprehensive model of a modern automotive turbocharged Diesel engine.© 2003 ASME

Simulation Model of an Axial Piston Pump Inclusive of Cavitation

A mathematical model of an axial piston pump is presented. The numerical model is based on a finite volume concept. The pump has been divided in different volumes where fluid properties are assumed homogeneous. Since the reduction of the pressure pulsations is one of the most important aims of pump builders, the effects of the port plate relief groove design have been carefully modelled. The gaseous cavitation has been considered in a simplified manner. The pump has been modified in order to measure the fluid pressure inside one of the cylinders; therefore a conduit has been realized to connect the cylinder chamber to a pressure transducer that is placed in a non-rotating position. The fluid pressure inside the conduit has been modelled with a one dimensional scheme for unsteady flow. The code has been tested and calibrated by comparing its numerical results with a set of experimental data. The potentials of the code are presented, spanning over different geometries.Copyright

Analysis and Design of Direct Steam Injection for Tomato Concentrate Sterilization

Abstract Direct steam injection is a sterilization technique which is often used for high-viscosity fluid food, when the preservation of the quality characteristics and energy efficiency are the priority. In this work, an apparatus for the sterilization of tomato concentrate has been analyzed by means of a 3D computational fluid dynamics (CFD) model, in order to optimize the exchanger performance in terms of temperature distribution inside the product. A multidimensional two-phase model of steam injection inside a non-Newtonian pseudoplastic fluid was adopted to evaluate the thermal history of the product and the condensation rate of the steam injected in the heat exchanger during the thermal process. Subsequently, the CFD analysis has been extended to examine the effects of the different process parameters (sterilization temperature, steam flow rate, radial and axial temperature profiles and nozzle geometry) on the resulting product. Results obtained allowed to understand the effects of process parameters on the behavior of the condensing steam and obtain better performance of the exchanger in terms of temperature distribution of the treated product.