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Heavy-duty centrifugal fans are employed for the transport of dust-laden flows in industrial plants, for cement or steel production, or in energy production of plants and mine ventilation systems. These applications require the disposal of huge amounts of suspended particles, which can lead to a gradual erosion of the machine parts where impacts take place. The wear of the fan components can lead to premature failure of the machine, threatening human safety and reliability of the whole plant. The assessment of the wear severity of the machine, according to the process parameters, can aid the plant owner in scheduling overhaul operations along with the operative life of the machine. Moreover, through a reliable estimation of the wear severity, fan manufacturers can optimize the whole machine design process, from the material selection to the warranty time assessment. This work aims to develop a semi-empirical method capable of estimating the erosion severity of centrifugal fans employed for heavy-duty operations. A mechanistic model which accounts for the erosion on the blade leading edge is proposed. The model is derived by means of an analytical approach and accounts for a number of operating parameters (i.e.,, fan geometry, fan operating point, particle concentration in the flow, fluid properties, and material erosion resistance). A comparison of the theoretical model to the computational fluid dynamic (CFD) simulation results obtained through the use of multiphase particle tracking is also provided to assess the reliability of the present method.

Electrical and fossil fuel powered vehicles require to reject some form of heat produced as a byproduct of their operating principle. This task is performed by radiators, typically equipped with axial flow fans to maximize the specific processed flow rate. These fans, as well as all the other fans that typically equip the vehicles (e.g., for HVAC purposes), are required to be very efficient and to produce a minimum level of noise. In this framework it is of crucial importance to adopt all the tools that can help in understanding the source of inefficiency and noise. This work presents the adoption of Computational Fluid Dynamics (CFD) as a possible tool for the investigation of the fluid dynamics of an axial flow fan. In order to let CFD become routinely employed, a sequence of validation steps is required by industries. In this work, two different CFD tools (ANSYS-CFX and OpenFOAM-v2006) are employed and the results of the investigation are compared to experimental data for assessing the reliability and the accuracy of each of these tools. Experimental data are obtained with two test benches: one build in compliance with ANSI/AMCA standards for airflow performance evaluation and one ad hoc developed for PIV measurements (i.e. flow field visualization). The capability of the CFD softwares of correctly replicating the fan performance and flow field even in this complex set-up (due to the loose constraints of the fluid flow) is shown both with steady and transient simulations.

Gas turbines can operate in an environment dispersed with particles that, if ingested by the machine, may have a detrimental effect on the aerodynamic performances. Therefore, the aim of this work is to gather information about how particles adhesion is influenced by geometrical features of gradually growing complexity. At this scope, the particle deposition problem is investigated from the numerical standpoint. Specifically, the LS-89 transonic high pressure turbine (HPT) vane is simulated and an encounter with a volcanic ash cloud is modelled. Three simulations are carried out: a 2D simulation has been compared with the set of 3D simulations. Different levels of complexity of the geometry have been considered for the 3D case: the endwall effect has been assessed considering the presence of a variable radius fillet and comparing it with the prediction obtained by a cylindrical extrusion. The proposed analysis provides indications on the 2D and 3D prediction with regards to particle deposition problems. The sticking pattern of the particle has been investigated in relation to the different nature of secondary flows.

In recent years, CFD has proven to be a very useful asset to help with predicting complex flows in a wide range of situations, including multiphase and gas-particle flows. On this track, numerical modelling of particle-laden flows in multistage turbomachinery has become an important step in helping to analyse the behaviour of a discrete phase in gas turbines. Furthermore, unsteady effects due, for example, to rotor–stator interaction may have an effect on trajectories and capture efficiencies of the discrete phase. Unfortunately, computational times for transient simulations can be exceedingly high, especially if a discrete-phase needs also to be simulated. For this reason, this work reports a new method for the efficient and accurate simulation of particle-laden flows in gas turbine engines components. The Harmonic Balance Method is exploited to gain orders of magnitude speedup exploiting the idea that once the flow field has been embedded in the spectral basis, it can be reconstructed at any desired time. In this way, not only can the computational time needed to reach convergence of the flow field be dramatically reduced, but there is also no need to keep simulating the flow field during particle tracking. On the contrary, the continuous phase field can be retrieved at any desired time through flow reconstruction. This technique is conceptually simple, but, to the authors’ knowledge, has never been applied so far in particle-laden flow simulations and represents a novelty in the field. First, the implementation of the method is described, and details are given on how phase-lagged boundary conditions can be applied to flow and particles to further speed up the calculation. Then, some relevant case studies are presented to highlight the performance of the method.

Numerical simulations of particle-laden flows have received growing attention in the last decade, due to the broad spectrum of industrial applications in which discrete phases prediction is of interest. Among these, ingestion of particles by turbomachinery is an area that is seeing vivid research and studies. The most common technique to tackle this kind of problem is the Eulerian-Lagrangian method, in which individual particles are tracked inside the domain. At the same time, in multi-stage turbomachinery simulations interfaces are needed to couple the flow solution in adjacent domains in relative motion. In this work, an open-source extension for Lagrangian simulations in multistage rotating machines is presented in the foam-extend environment. Firstly, a thorough discussion of the implementation is presented, with particular emphasis on particle passage through General Grid Interfaces (GGI) and mixing planes. Moreover, a mass-conservative particle redistribution technique is described, as such a property is requested at interfaces between Multiple Reference Frame (MRF). The peculiarities of the algorithm are then shown on a relevant test-case. Eventually, three turbomachinery applications are presented, with growing complexity, to show the capabilities of the numerical code in real-life applications. Simulation results in terms of erosion and impacts on aerodynamic surfaces are also presented as examples of possible parameters of interest in particle-laden flow computations.

The demand for quieter vehicles is pushing manufacturers of components for the automotive industry to seek for solutions to reduce the overall noise emissions. The cooling fan makes no exception: the aerodynamic interaction of the blades with the incoming flow generates turbulence and pressure fluctuations which ultimately translate into noise generation. A variety of expedients have been introduced to limit the produced noise, but no univocal solution has been found. In modern research, Computational Fluid Dynamics (CFD) has been successfully applied to blades and fans for both the flow and acoustic field derivation. By including the acoustic field, researchers have been able to predict the effect of changes in the blade geometry on the overall sound emission. This work reports a conjugate numerical-experimental study of a reference profile in different flow conditions, in order to validate the CFD acoustic prediction and to lay the basis for improved candidates able to lower the fan-generated noise.

Computational fluid dynamics (CFD) is increasingly used during the design phase of turbomachinery. Reducing the cost of such computations is one of the major challenges in the industrial field. The multi-physics phenomena and the multidisciplinary interactions needed for the design of the engine components are difficult to be faced with the classical design methods. In addition, the interest of manufacturers and operators of turbomachines in the increase in performance when degradation processes occur is growing. In the aeronautical sector degradation is among the most critical issues, as it can lead to the in-flight shutdown of the engine. In a bid to tackle these big problems, new design methods based on approximation techniques have been developed. These techniques are called surrogate models and are currently the most used design methods for the aerodynamic design of aircraft engines. In this work, the assessment of a surrogate surface built for the purpose of optimizing an HPT vane in degrading conditions is performed. Using machine learning and statistical techniques, a sensitivity analysis is conducted in order to reduce the problem dimensions. The results of the sensitivity analysis are used for a study of the surrogate, with the purpose of obtaining design guidelines when deterioration effects are considered in the design phase. The main outcome of this study is a map, that outlines the best design zone defined by the combination of the most influential parameters.

The Harmonic Balance Method is one of the most commonly employed Reduced Order Models for turbomachinery calculations, since it leverages the signal sparsity in the frequency domain to cast the transient equations into a coupled set of steady-state ones. The present work aims at detailing the development and validation of a new framework for the application of the Harmonic Balance Method in the open-source software OpenFOAM. The paper is conceptually divided into building blocks for the implementation of the code. For each of these, theoretical notions and coding strategies are given, and an ad hoc validation test case is presented. This structure has been chosen with the aim of easing the reader in the understanding and implementation of such a method in a generic fluid dynamics solver. In a fully open source philosophy, the library files are freely accessible in the authors’ repository (link provided below in the text).

Particle ingestion is a major concern for the operation of gas turbines. In the case of an aircraft, particle dispersed in the air ingested by the engine can threaten flight safety. Swallowed particles can erode or stick to aerodynamic surfaces. Both the occurrences translate in a reduction of performance due to variation in shape and in roughness of the aerodynamic surfaces. This work is devoted to the analysis of fouling, i.e. the deposition of particles over time. By observing that the deposition pattern is strongly influenced by the flow field in the nearby of the walls, the central idea of this work is to employ Active Flow Control (AFC) to mitigate fouling when emergency conditions are met by the aircraft. The proposed system will inject air bled from compressor discharge in front of the critical locations where fouling is supposed to occur. The present work aspires to lay the foundations for the development of such an AFC device, by focusing on the modified aerodynamics consequent to the introduction of the transverse jet. The potential of this device is evaluated quantitatively using CFD simulations. An energy-based sticking model, coupled with a mesh-morphing solver, is used to track the airfoil deposition thickness evolution in time. The work is two-fold: first, the dynamics of the interaction between flow structures and particle transport is addressed. Second, the attention is posed on correlating fouling pattern variation to the modified aerodynamics of the vane consequent to the introduction of the device. Three design concepts are investigated on the 3D test case geometry of an HPT NGV cascade. The counter-rotating vortex pair (CVP) is detected as the main responsible for jet-particle interaction. Finally, the jet impact on aerodynamic performance is also assessed.