This study involved the use of Laser Doppler Anemometry (LDA) to measure air flows at high temporal and spatial resolution for the calibration of high-precision instrumentation, together with the use of Computational Fluid Dynamics (CFD) modelling tools. The work was performed in conjunction with BSRIA Instrument Solutions (BIS) with the main aim of improving the speed and accuracy of the calibration facilities within the BIS laboratory through the novel application of these technologies. Throughout the exploration of each facility, experimental LDA measurements, theory and virtual CFD models were compared to explore the airflow behaviour. In Part 1 of the investigation, this primarily focussed on a Balometer Calibration Facility (BCF – volume flow device) and an Open Jet Wind Tunnel (OJWT – air velocity device); both controlled using orifice plate pressure drops. The BCF was explored using attached sections of square ducting with optical access for LDA measurements. A traversing method was devised to measure volumetric flow rates, which were compared to the measured orifice plate pressure drops in order to achieve calibration of the facility. Comparing traversing methods showed that a Log-Tchebycheff method provided the most accurate prediction. The BCF calibration method was devised such that is could be applied to other volume flow facilities. These experimental measurements were compared with CFD simulations of ducted airflow in square and circular cross-section geometries for further analysis including the theoretical 1/7th power law velocity profile along with profile method comparisons. A further volume flow device, the Blower Door Calibraion Facility (BDCF) was investigated using a similar process to show the generality of the devised method. The OJWT, a facility typically used to calibrate velocity devices such as anemometers, was calibrated using a simple but novel calibration process involving LDA. To investigate further the OJWT behaviour, CFD models were created to represent OJWT with and without an anemometer and contrasted with equivalent experimental situations. A comparison of these experimental and computational data sets was performed showing representation of experimentally observed phenomena within the CFD model. This included so-called „blockage factors‟, mentioned below. iii In operation, to achieve the calibration of anemometers, the OJWT must make use of Blockage Factors (BFs) in order to correct the calibrated reference velocity to determine the actual velocity experienced by the unit under test. This was explored in Part 2 of the project. Experimental and computational (CFD) investigations were performed to explore the nature of the BFs towards a method of prediction. This would be of great use to industry as an anemometer calibration is not valid on an OJWT if an incorrect BF was applied. Outputs include: Novel methods of calibration were devised for test facilities which successfully achieved UK Accreditation Service (UKAS) certification. LDA was used to show that, in square ducts, the Log-Tchebycheff profiling method performs better than Equal Areas at providing an estimate for average cross sectional velocity when both low- and high- flow rates are considered. To verify CFD models of ducted airflow and of near-field measurements around an anemometer within an OJWT, LDA was shown to be a powerful tool. The basis for a method of BF prediction was proposed. This is based upon the empirical relationship between a statistical analysis of numerous calibrations along with an experimental LDA measurement of the deflection of air around an anemometer (Radius Expansion – RE). This is a first use within the industry and is an original contribution to knowledge. CFD models were also employed in the investigation of BFs, and the empirical relationship was applied to the data extracted from these simulations. Results closely matching the expected values were produced. The empirical relationship (between RE and BF) was demonstrated through estimation of the BF of an unknown Kimo 70 mm anemometer.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:634038 |
| Date | January 2014 |
| Creators | Mayes, Alex |
| Publisher | London South Bank University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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