1,721,246 research outputs found
Numerical investigation of the lean effects in centrifugal compressors
Full text linkThe continuous need of performance improvements in the centrifugal compressor technology for industrial and aeronautical applications, as well as the modern CAD techniques allow and ask for new impeller designs. In this paper a numerical analysis of opposite lean angles on the rotor blades is carried out. These methodologies are widely applied to axial turbomachines, but few papers in the open literature can be found on centrifugal compressors. Blade lean effects on the rotor outlet flow and the vaneless diffuser performances are discussed. Some of the blades have been tested for 3 tip clearances and 3 flow rates to get a deeper understanding of the involved phenomena. Results show a slight dependence of the rotor efficiency on rotor blade lean; notwithstanding, the local flow field at the rotor outlet presents different patterns that affect the flow evolution in the vaneless diffuser and its performances
Properties and energy performance of wood waste sustainable panels resulting from the fabrication of innovative monolithic aerogel glazing systems
No full textThe combined effect of pine wood waste panels resulting from the different industrial processes to produce window frames and double glazing systems with monolithic aerogel of different hydrophobicity in the gap on the heating, cooling, and artificial lighting energy demand of a typical 70 s residential building in different climatic conditions is evaluated. The scraps obtained from the production of the innovative transparent glazing systems are used to fabricate eco-sustainable panels using natural flour-based glue. A thermal conductivity value of the opaque panels equal to 0.077 W/mK is measured by means of a thermal flux meter methodology. As regards the glazing systems, thermal resistance values of 0.86 and 0.92 m2K/W are measured for hydrophilic HY 0 and hydrophobic HY 10 unit, respectively; as a consequence, a thermal transmittance reduction equal to 65-67 % is obtained with respect to the double glazing unit with air in the gap. However, visible transmittance equal to 0.66 is measured as increasing hydrophobicity with respect to 0.81 of the conventional air glazing unit (reduction of 16 and 19 % with HY 0 and HY 10, respectively), as measured by means of a large integrating sphere spectrophotometer. The experimental data measured on eco-sustainable opaque panels and innovative transparent solutions are implemented in dynamic simulation models. The results show an annual heating energy demand reductions (in the 17 (Bolzano) - 39 % (Palermo) range) and cooling (in the 2 (Bolzano) - 11 % (Rome) range) in different climatic areas. Hydrophobicity has a negligible influence on the results. On the other hand, the energy demand for artificial lighting is not affected by the investigated solutions (maximum increase of 10 % is obtained in Bolzano with hydrophobic glazing system). This work is preparatory for the future possibility of starting a production chain of wood fiber insulating panels in the area, which will be in case fabricated at industrial scale in order to reduce the environmental impacts in the construction process of a building in a circular economy perspective and to improve the energy efficiency of the building envelopes by means of innovative materials
Lighting of Museums and Art Galleries
No full textA museum is a place where people can explore and learn the past, the present and the future of culture and science. Amongst the other technical systems, the lighting equipment must satisfy a number of requirements. For each project, lighting designers must face challenges in order to encompass the given specifications in a single lighting concept: protection of the artefacts, economic convenience, architectural constraints and, last but not least, the creative ambitions of the artist. This paper analyses the lighting environment of a real art gallery with the aim to identify a satisfactory solution in terms of enjoyment, artefact preservation and energy consumption. By means of a simulation software, suitable general and spot lighting devices are chosen to fulfil the requirements whilst avoiding damages to the artefacts, and lighting parameters are obtained to evaluate the proposed solution. The work shows that advanced LED technologies can be effectively used to modify a museum lighting environment and turn it into the classical gallery archetype
A psycho-acoustical experiment using a stereo dipole for spatial impression of music signals
No full textAcoustic performance of concert halls and opera houses is usually assessed by measuring the BIRs (Binaural Impulse Responses). Anechoic music convoluted with BIRs constitutes the virtual sound in the way it is played in the sound field, i.e. the room. From BIRs, the IACC (Inter-Aural Cross Correlation) can be computed. This parameter makes it possible to evaluate the spaciousness of the hall. However, the calculation of the IACC value is affected by the convolution technique used as well as the kind of musical motif. For example, in the same concert hall, the BIR provides three different IACC values in the case of three different motifs played in it. This study has conducted a psycho-acoustic experiment by using a virtual sound field representation produced by the stereo dipole technique in a listening room. In the experimental set-up there were two or four loudspeakers, corresponding to the single stereo-dipole or the dual stereo-dipole, respectively. By cancelling the cross-talk pathways (i.e. from left loudspeaker to right ear), the parallel sound presentation creates a 3D sound field for listeners sitting in the target point. The invert Kirkeby method was adopted to determine the inverse filters. Finally, the auralization technique with measured BIRs in theatres was utilized and the virtual sound field was generated in the Arlecchino listening room (Bologna, Italy), a low reverberation room equipped with an Ambisonic system. In the virtual sound field, the BIR was recorded again by the same dummy head used during the measurement in the theatres. The similarity between real and virtual sound fields was evaluated by comparing some acoustic parameters. The stereo-dipole technique demonstrates a good degree of accuracy of the sound field appearance. Moreover, the accuracy of the sound field appearance was analysed using two musical motifs and three musical instruments, comparing the values of the IACC calculated by echoic music with the virtual echoic music
Water vapour permeability of innovative building materials from different waste
No full textThe hygrothermal performance of building materials is a very important issue for indoor comfort. The aim of this study is to measure the water vapour resistance factor μ of recycled waste materials. Leather cuttings, rice husk, and coffee chaff were used in order to manufacture innovative panels for thermal-noise building insulation. The permeability measurements were carried out by the dry cup method in compliance with the Standard EN ISO 12572. In the experimental campaign, conventional gypsum plaster and expanded polystyrene were also considered, whose hygrothermal characteristics are known from the Literature, in order to verify the reliability of the method. The moisture transfer properties of the innovative panels are higher than the values available in the Literature for other vegetable and mineral fibers-based panels (sheep wool, wood, cork, expanded vermiculite and perlite, glass or stone wool, and so on). However, the high μ-value obtained for coffee chaff panels (equal to 392) could involve an increase in heat loss and acoustically weak points
The acoustic simulation of performing area in the auditorium: Some examples in Italy
No full textThe design of auditoria and opera houses requires particular care for the stage area, where several different requirements should be achieved for the performers. Among these, the acoustic quality represents a fundamental aspect, and it differs from the listeners' perspective. Moreover, the performing area in concert halls is often an important area for non-acoustic reasons, since lighting, thermal plants, etc. are often placed in this special zone, and should be properly designed in order to guarantee a high level of global comfort. This paper presents some examples of how to design exhibition zones in opera houses and auditoriums that show both acoustic and technical improvements, both in theory and in architecture
On the use of 3d auralisation to evaluate room acoustic enhancement in auditorium restoration
No full textThe acoustic quality in auditorium and concert halls is normally evaluated by the measurements of Impulse responses (monaural, binaural or even MIMO). The subjective evaluation is often obtained by convolving anechoic music with the measured IRs. The psycho-acoustical experiment is achieved using a virtual sound field representation. At the University of Bologna, the listening room Arlecchino includes Ambisonics and stereo dipole techniques for playback. In this paper, two different Italian opera houses and two Japanese concert halls were analysed. They were the Teatro Nuovo in Spoleto (Italy), the Teatro Alighieri in Ravenna (Italy), the Kirishima International Musical Hall in Kagoshima (Japan), and the Tsuyama Musical Cultural Hall in Okayama (Japan). The similarity between real and virtual sound fields, obtained with stereo dipole technique, was evaluated by comparing different acoustic parameters calculated by real and virtual sound fields, in the four halls in different designed configurations. Finally, the stereo dipole technique was added to the ambisonic methodology to reproduce the sound fields for the psycho-acoustical experiment. The dual stereo-dipole technique using two kinds of cross-talk cancelling filters can be one of the solutions for improving the acoustical quality of home theatre
Validation and application of three-dimensional auralisation during concert hall renovation
Full text linkDuring the renovation of auditoria and concert halls, the acoustic quality is normally evaluated from measurements of impulse responses. One possibility for evaluating the acoustic quality from the measurements (the simulations) consists of convolving anechoic music with the measured (or simulated) impulse responses. In this way, a psycho-acoustic test is achieved using a virtual sound field representation. The listening room ‘Arlecchino’ at the University of Bologna includes ambisonics (up to fifth order) and stereo-dipole playback for virtual reproduction of sound in rooms. In this article, the effectiveness of the listening room ‘Arlecchino’ is first analysed, comparing acoustic parameters obtained from binaural impulse responses measured in some opera houses (in Italy) and auditorium (in Japan) with those virtually measured after the virtual reconstruction obtained in the listening rooms. The similarity between real and virtual sound fields, has been evaluated by comparing different acoustic parameters calculated by real and virtual sound fields, in four halls in different configurations, by means of the stereo-dipole method. In the second part of the article, the listening room was used to analyse the variation in interaural cross-correlation measurements in rooms obtained considering different anechoic sound signals convolved with the binaural impulse responses, to quantify the variation of the interaural cross correlation with different motifs. For this purpose, two different musical instrument digital interface musical motifs, very different from each other for their music characteristics, have been considered. Moreover, for each musical motif, different sound characteristics (i.e. different musical instruments) were considered, to consider both the rhythmic and timbre aspect
On the influence of thermo-hygrometric conditions in 3D acoustic measurements
Full text linkWithin the frame of SIPARIO, a project recently funded by the Italian region Emilia Romagna, it aims to virtually reconstruct both 3D audio and 360circ video of real performances by recording and undertaking acoustic measurements inside the most historical theatres and concert halls spread all over the Europe. However, the measurement of multi-channels IRs is influenced by several other factors, including thermo-hygrometric conditions. This paper deals with the experimental analysis concerning the influence of temperature, relative humidity, and air velocity on acoustic parameters. Thermo-hygrometric variables have been varied and the variation of several room acoustic parameters has been analized. The data have been collected in order to obtained a relation between the variation of the acoustic parameters with the variation of the thermo-hygrometric variables. In further steps, a statistical analysis will be conducted to determine possible correlations between room acoustic parameters and thermo-hygrometric parameters
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