This paper reports the external convective heat transfer in an innovative lowpressure vane, designed with a multi-splitter configuration. Three aerodynamic airfoils are positioned in between larger structural vanes, replacing struts presently used in current aero-engines, which results in superior aerodynamic performance. Static pressure and heat flux measurements were carried out in the large compression tube facility of the von Karman Institute, using pneumatic taps and single-layered thin film gauges respectively. The steady and unsteady heat transfer distributions were obtained at representative conditions of modern aeroengines, with M 2,is close to unity and a Reynolds number of approximately 10 6 . This facility is specially suited to control the gas-to-wall temperature ratio that drives transition mechanisms. The heat transfer across the multi-splittered passages is confronted with correlations on ducts to further characterize the boundary layer status. The data will be used to guide code developers by verifying their boundary layer transition models, and designers by showing the areas of the vane where heat transfer is most sensitive to the off-design conditions.

The aim of this work is to accelerate an existing two-dimensional explicit Euler solver implemented on a single CPU. The solver based on Discontinuous-Galerkin method for the spatial discretization is ported to run on a graphical processing units (GPU) using the CUDA programming language.
The input has been rearranged in one-dimensional buffers to maximize the profit from the GPU SIMD architecture. A GPU implementation of the explicit solver has been performed. The GPU implementation runs on a Tesla C1060 GPU and a Tesla K20
GPU. The CPU implementation has been also extended to run on multi-core CPU over OpenMP. The multi-CPU program runs on a hyper-threaded E5540 Intel Xeon processor.
Peak speedup of 66x has been achieved for the simulation of an acoustic pulse between GPU and single CPU implementation and peak speedup of 6x between the GPU and multiple CPUs implementation.

NACA 65-series airfoils feature a cusped trailing edge impractical for mass-production manufacturing processes. The effects of two different trailing edge modifications on NACA 65-810 blades on the performance of a low-speed rotor-only axial fan were investigated. Two rotors were realized and experimentally tested at two different tip leakage values. Experimental data were compared each other and with results of CFD calculations performed on the ideal geometry. The comparison shows the performance losses of the actual geometries against the ideal one. These losses must be taken into account when blade design is based on cascade data. Indications on the best modification strategy are also suggested.

The paper presents a historical overview of the developments of aerodynamic design methods for low-speed axial-flow fans. This historical overview starts from the first fan applications, dating back to the 16th century, and arrives to the modern times of computer-based design techniques, passing through the pioneering times of aerodynamic theories and the times of designing before computers. The overview shows that the major achievements in the axial fan design discipline have actually been related to other technological fields, such as marine and aeronautical propulsion, as well as to the development of wind tunnels. At the end of the paper, the reader will have acquired a complete panorama of how the historical developments of the discipline have brought us to the current state of the art.

This dissertation treats the aerodynamic design of low-speed axial fans for industrial applications, considering dimensional and/or rotor-speed constraints as eventual additional design requirements.

In the last years, the complexity of the design task and the number of
related tools have increased exponentially in turbomachinery, with industrial axial-flow fans making no exception. Recent automated design softwares and optimization routines provide highly efficient fan designs. Regardless of the effectiveness of these computer-based methods however, the variables that mostly affect fan performance and efficiency are still related to the basic primary design choices, as the selection of the axial fan configuration, for instance.

In spite of a long history of axial fans, some basic questions on the aerodynamic design of these machines still do not have a clear and definitive answer in the technical literature. In particular, two major design issues have been identified:

a) the lack of quantitative indications that guide the designer into the selection of the axial fan configuration, among rotor-only, rotor-straightener, preswirler-rotor, and multistage machine;

b) the lack of quantitative information that guide the fan designer into the choice of the suitable span-wise aerodynamic loading distribution (i.e., the design vortex criterion) for the required operation in case of rotor-only axial fans.

According to these needs, a research has been conducted into several aspects of the aerodynamic design of low-speed axial fans. A data-base of fan performance and efficiencies has been collected to provide maps that can guide fan designers into the primary design choices reported at items a) and b). The construction of this data-base required the collection of fan data from the available literature and from a dedicated experimental campaign. Most of the fans that have been tested on two ISO 5801 inlet-chamber test rigs are specifically-designed rotor-only prototypes. Therefore, an effective aerodynamic design method has been developed for this widely used type of machine (i.e., for rotor-only axial fans). The method is based on the
information resulting from the fan data-base, as well as on a preliminary mean-line performance and efficiency estimation procedure. The local (i.e., the velocity field) and global (i.e., performance and efficiency) behavior of the resulting geometries have been verified by means of a CFD (Computational Fluid Dynamic) model, before the manufacturing of the prototypes.
CFD simulations are run on a simplified model that is particularly appropriate for the industrial requirements of rapidity and accuracy of results. All the necessary information to perform satisfactorily the aerodynamic design of a rotor-only fan are provided. Most of these indications can be directly extended to design also machines with fixed bladings.

The main results of the investigation are graphs that summarize axial fan performance around the well-known Cordier curve, identifying: i) suitable operating areas for each fan configuration, and ii) suitable vortex-criteria operating areas in case of rotor-only fans. Theoretical explanations are provided at support of the observed trends. Such information represent simple and quantitative aids to guide fan designers into the primary design choices.

In particular, the data show that vane-axial and contra-rotating fans operate at lower specific speeds and diameters with respect to rotor-only ones. Thus, a Cordier-line diagram specific for Rotor-only axial fans relies at higher specific diameters with respect to vane-axial machines. Whether the rotor-only configuration is the only one permitted (for instance due to dimensional constraints), Forced-vortex rotors (i.e., with aerodynamic loading distributions that increase towards the blade tip) represent a suitable solution for operations at low specific speeds, relatively large flow-rates and pressure rises. However, the fan efficiency of forced-vortex rotor-only fans is lower than that of rotor-straightener machines operating at the same pressure-rise, making the forced-vortex design solution appropriate in presence of constraints on both the fan axial length, the fan diameter and the rotor speed (for instance, the fans installed on air-conditioner external units).

The scope of the work is providing an aerodynamic design methodology for industrial axial fans. The information reported in this work can be useful for fan designers and manufacturers, as well as for anyone interested in the field of mechanical ventilation.

The variety of shapes and sizes among daggerboards and rudders of small racing yachts indicates the lack of a comparative design method and that some aspects may be neglected in the designs currently proposed. In particular, a literature survey showed that: (i) the conventional design approaches are exclusively based on upwind conditions, disregarding any downwind contribution to the race, (ii) the detrimental effects related to the typically low Reynolds numbers involved are marginally considered, and (iii) there are ambiguous indications about sweep angle effects on foil performance. In this paper, a design method based on a Velocity Prediction Program compares different appendage planforms for a yacht, identifying the ones minimizing the overall racing time, sum of upwind and downwind contributions. The method is applied to a 4.6 m skiff and the performance of the daggerboards analysed are compared with xflr5 simulations, validated against experimental tests. The results quantify the time gains of longer foils and the similar performance of elliptic and rectangular geometries with equal drafts but different aspect ratios. Swept foils are investigated as well, showing lower lift curve slopes compared to straight geometries for the high aspect ratios typically used on small yachts.

The paper presents a historical overview of the developments of aerodynamic design methods for low-speed axial-flow fans. This historical overview starts from the first fan applications, dating back to the 16th century, and arrives to the modern times of computer-based design techniques, passing through the pioneering times of aerodynamic theories and the times of designing before computers. The overview shows that the major achievements in the axial fan design discipline have actually been related to other technological fields, such as marine and aeronautical propulsion, as well as to the development of wind tunnels. At the end of the paper, the reader will have acquired a complete panorama of how the historical developments of the discipline have brought us to the current state of the art.

NACA 65-series airfoilsfeature a cusped trailing edge impractical for mass-production manufacturing processes. The effects of two different trailing edge modifications on NACA 65-810 blades on the performance of a low-speed rotoronly axial fan were investigated. Two rotors were realized and experimentally tested at two different tip leakage values. Experimental datawere compared each other and with results of CFD calculations performed on the ideal geometry. The comparison shows the performance losses of the actual geometriesagainst the ideal one. These losses must be taken into account when blade design is based on cascade data. Indications on the best modification strategy are also suggested.

Rotor-only axial fans feature rotors designed according to different vortex criteria. Nowadays the literature does not exhaustively clarify when a specific swirl distribution has to be used and which are the advantages/drawbacks in terms of fan performance and efficiency. A review of the experimental performance of rotor-only axial fans designed with different vortex criteria is summarized here in Φ − Ψ and σ − δ (specific speed-specific diameter) graphs to identify the best operating conditions of each design. Four rotor-only axial fans (two free-vortex, a constant-swirl and a rigid-body swirl one) are tested on an ISO-5801-A rig. For two of them, flow velocities at rotor exit are measured with a 5-hole probe. The result is an experimentally based map around the Cordier curve for rotor-only axial fans. Indications on the best Φ − Ψ range for fans designed using different vortex criteria are provided and explained. The effects of increasing the tip clearance on the rotor performance at design duty are investigated as well.

Rotor-only axial fans feature rotors designed according to different vortex criteria. Nowadays the literature does not exhaustively clarify when a specific swirl distribution has to be used and which are the advantages/drawbacks in terms of fan performance and efficiency. A review of the experimental performance of rotor-only axial fans designed with different vortex criteria is summarized here in Φ − Ψ and σ − δ (specific speed-specific diameter) graphs to identify the best operating conditions of each design. Four rotor-only axial fans (two free-vortex, a constant-swirl and a rigid-body swirl one) are tested on an ISO-5801-A rig. For two of them, flow velocities at rotor exit are measured with a 5-hole probe. The result is an experimentally based map around the Cordier curve for rotor-only axial fans. Indications on the best Φ − Ψ range for fans designed using different vortex criteria are provided and explained. The effects of increasing the tip clearance on the rotor performance at design duty are investigated as well.