"Application of Infrared Thermography for Boundary Layer Inspection of Subsonic Flows in Passive Mode: a New Data Post-Processing Technique"
In thermo-fluid-dynamics, it is known the important role played by boundary la yer.
Therefore, the present paper wants to dwell on the possibility to enlarge the application of infrared thermography for flow analysis, in particular for subsonic flows in passive mode.
These conditions point out difficult measurement problems for the low energy content. In order to overcome this drawback, a high thermal resolution camera has been chosen and used. Moreover the camera has been experimentally characterized in order to define its modulation transfer function and to provide a software tool for data restoration.
Successively, tests have been carried out in a subsonic no-cooled closed loop wind tunnel.
That is, during the start-up of facility, a natural air heating is produced by exchange with fan.
However, the latter is not localized and equal to few degrees during the whole run. In this way, problems own of active technique are avoided and measurement can be performed in subsonic flows. At least, a new theoretical model has been defined to correlate superficial body temperature maps to convective coefficient distribution.
It has been pointed out for semi- infinite slab in thermal transient conditions and for a continuous convective exchange between air and body. In particular, it has been applied for boundary layer inspection in a Fokker airfoil, whose results are presented in this paper for zero angle of attach, as test case for the new measurement and data processing technique here proposed.
"Definition of FBG sensor photoelastic coefficient by laser Doppler vibrometry"
In this work a system for static and dynamic calibration of in-fibre Bragg grating sensors is described. Our idea starts from the calibration procedure of strain gauges that is done by applying a pure bending on the sample.
The aim of this work is to develop a system that allows as to apply an analogous experimental technique.
In this case we use as reference a Laser Vibrometer, for this reason we need to impose to the sample a dynamic excitation. With the system developed is possible to apply a sinusoidal force in a symmetrical way in order to obtain an alternate pure bending in the area in which the sensor is positioned.
The greatest excitation frequency is about 10-20 Hz, depending on the characteristics of FBG interrogation system.
"Measurement and modelling techniques to approach the problem of noise reduction of domestic range hood"
A combined experimental and theoretical methodology is proposed to approach the problem of noise reduction of range hoods.
The experimental approach is based on the use of simple microphones and accelerometers to have a quick characterization of the noise spectrum and vibration characteristics of different models of this product.
The second phase is based on the theoretical modelling of the structural vibrations and flows by FEM and CFD codes in order to better understand and identify the main noise sources.
Once identified the main problems some work prototypes of range hood has been realized and the possibility of noise reduction quantified by sound power estimation by acoustic intensity measurement techniques.
"Characterization of professional knives by thermoelasticity"
In this work the mechanical behaviour of the blade, has been studied using thermoelastic analysis.
This measurement technique permit to correlate the thermal variation, induced by a cyclic load, with the stresses distribution on the knife blade.
The image of superficial stresses acquired by thermoelastic system (Deltatherm 1550) has been compared with FEM analysis results directly.
"An innovative methodology in the characterization of halogen lamp as reference source for Heat Flux Sensors calibration"
In radiant heat flux probe calibration, the possibility of obtaining a known source is achieved by the employment of a cavity as similar as possible to a black body.
That is, using common radiation laws, it is possible to monitor the produced heat flux from its temperature control and measurement.
However, many drawbacks are present in traditional testing and calibration procedures.
The employment of cavities with high production costs and non-flexible configurations presents some negative aspects.
For this reason, it can be helpful to introduce the use of the halogen lamp in radiant heat flux sensor (HFS) calibration. Even if a more complex study is required just to characterize this type of source, it results in a cheaper and easier-to-use method in all laboratory testing benches when compared to common furnaces.
Moreover, the high generation capability and efficiency represent very desirable properties.
These aspects justify the initially more time consuming setting procedure. That is, a possible approach for defining lamp features in HFS calibration is proposed in this work.
With this aim, a no-contact heat flux measurement is introduced, called the ‘skin technique’. Even if the latter points out the final result using the black body laws, the operating principle is different and permits one to experimentally characterize the lamp.
Moreover, a theoretical discussion of the emission properties is also given, carrying out a method to optimize the number and dimension of filaments of the lamp as a function of the needed heat flux uniformity. In this step no classical view factors are employed, but starting with Lambert’s law, a proper view factor is defined for the set-up. Finally, a specific application is discussed for the calibration of a HFS used in a plasma jet.
"Boundary Layer Inspection in Sub-Sonic Flows by High Sensitive Infrared Thermography"
In any aerodynamic phenomenon, boundary layer plays a fundamental role, conditioning the transition and detachment regions.
That is, many advanced techniques have been developed to monitor this aspect.
However, each one presents some drawbacks and the possibility to operate in a different way should be of interest.
The employment of infrared thermography is proposed differently from the classical procedures.
Up to now, only supersonic flow field has been analyzed, using the socalled passive technique, completely non-intrusive.
In this paper, the new possibilities offered by recently developed high sensitive thermographic arrays are analyzed.
Preliminary tests in subsonic flows have been performed in order to get useful full-field measurements in transportation vehicles as motorcycles.
"Structural behaviour characterization of the heart valve using a laser Doppler vibrometer and thermoelasticity"
In this job a methodology of study of the structural behaviour of heart valves has been approached through the employment both the thermoelasticity and laser Doppler systems.
A test bench has been realized with the purpose to fix the body of the valve and to excite the parts of remarkable importance from the structural point of view by means of a shaker.
The vibrational measurements have been adopted as boundary condition for the FEM simulations and the relative maps in terms of stress have subsequently been validate through the employment of the thermoelasticity.
"Distribuzione di Pressione Misurata all'Impugnatura di Macchine Vibranti Mediante l'Applicazione di Matrici di Sensori Capacitivi"
"Misure Laser nei Controlli Strutturali"
"An optical Cross-correlator implemented for torque measurement "
"Nuove tipologie di sensori ottici per misure di deformazione e temperatura testati tramite tecnica termoelastica"
"No-contact torque measurement by means of optic cross-correlator device"
"Stress measurement transmitted by bearings and joint on high-performance engine support"
"Preload measurement transmitted by a couple of rolling bearings, inside high-velocity electro mandrel, by using FBG sensors"
"Pressure distribution measurement over chain saw handles by the application of a new capacitive matrix"
A new type of sensor matrix is now available in order to measure operator’s hand-arm system pressure distribution in the hand-held machine/tool field.
The matrix is based on a series of capacitive sensors which vary the capacity depending on the pressure applied on their surface.
Matrix thickness and flexibility characteristics and its high sensitivity of monitoring pressure distribution make this tool particularly suitable to hand-held machine/tool field application.
The matrix has been here applied to chain saw handles, during tests performed complying with the actual standard.
"Improvement of thermoelastic measurement systems by modulation transfer function image correction"
In this paper, the problem of uncertainty in measurements of high stress gradients with reduced spatial resolution using a thermoelastic measurement system is addressed.
In these conditions, aliasing effects must be considered. The smoothing of the spatial gradients due to optical transfer function of the system has to be measured in order to define and correct systematic errors in the estimation of peaks stress values.
These problems are here analysed from a theoretical point of view. A data processing technique to make a possible correction by using the modulation transfer function is presented.
A typical measurement condition is also illustrated: a rotating wheel with a hollow hub, impacting a step profile.
This causes a high stress gradient around each hole. The latter is monitored by few pixels and low spatial resolution is present. That is, it is a typical situation of interest in detecting stress peak values.
The effects of the correction technique proposed are herein illustrated.