Investigation On The Methods Of Parameter Measurement And Calibration For Small Return-Flow Icing Wind Tunnels

It is a difficult and time-consuming task to find natural icing conditions for which the cloud parameters such as the liquid water content(LWC)and the medium volume diameter(MVD)are required to comply with the airworthiness certification.However,by refrigeration and spray systems,icing wind tunnel(IWT)can simulate low-temperature icing cloud environments in which many experiments can be accomplished with low cost but high safety.Compared with the flight test in natural environment,IWT test shows the advantages of low cost,high efficiency and safety.As the main ground facility for aircraft icing simulation and aircraft anti-icing and de-icing investigation,IWT plays an important role in both military and civil aviation applications.In addition,figuring out the measurement and calibration of IWT test parameters is the first step to conduct IWT tests correctly.The design and construction of the icing wind tunnel at Nanjing University of Aeronautics and Astronautics(NUAA)is a closed recirculation IWT laboratory.Lots of scientific and engineering issues exist in its design and construction.In this dissertation,both the measurement and calibration of LWC and MVD in IWT are investigated.Based on the ultrasonic pulse-echo method,a novel icing thickness measurement method is presented.The main results obtained are as follows.The measurements of the maximum wind speed,the dynamic-pressure stability coefficient,the axial static pressure gradient,the non-uniformity of velocity field in the test section,the field uniformity of section in the test section,the turbulence distribution and the wind energy ratio of the IWT at NUAA are carried out based on China national military standards GJB1179-91(Specification for flow quality of high and low speed wind tunnels),which are taken as the reference of the reports on flow field tests calibration of ordinary wind tunnels.The flow quality of the IWT is obtained.A calculation method for the variation of droplets parameters in the air flow is studied.A droplet-air two-phase mixture flow model of the movement of droplets for small icing wind tunnels is developed based on the Lagrangian method and the movement of one single droplet after being sprayed together with the heat and mass transfer characteristics are obtained.A method for calculating the required length of rectification section for droplets movement is proposed based on the changing laws of droplet parameters.The impact of parameters such as droplet diameter,temperature and velocity of airflow on the movement process of droplets and required rectification section length is analyzed.The results show that the required length of rectification section,the diameter and the temperature of droplets are obviously related with the parameters of air inflow.The prediction results may provide some guidance for the design and experiment of icing wind tunnels in the future.For the MVD measurement of the small icing wind tunnels,a simple method for measuring the water droplet diameter by laser particle size analyzer is proposed.Meanwhile,the calibration of MVD is carried out based on rotating multi-cylinder method.According to the icing accumulation characteristics of rotating multi-cylinder,the rime ice accumulation on a two-dimension rotating cylinder is simulated.In combination with the successive approximation method,a software for analysis of parameters of rotating multi-cylinder testing is developed.The calibration results agree well with the measured data,and which indicates that the method developed is validated to be used for the rapid MVD measurement.At the same time,the LWC measurement of the IWT of NUAA is conducted by using the sponge water collecting method,and the calibration is carried out by the icing blade method.In the meanwhile,the Euler method is used to calculate the efficiency in collection of icing blades.The experimental results show that the errors are acceptable,and the two sets of data are in good agreement.The theoretical principle of the ice thickness measurement based on the ultrasonic pulse-echo(UPE)method is mainly introduced.The research on ice thickness measurement is carried out by UPE technique.The feasibility of applying UPE method to ice thickness measurement is explored.Investigation on distinguishing rime ice and glaze ice in IWT test is carried out.The ice thickness is successfully measured real-time in the IWT.Finally,the whole work of the paper is summarized and prospected,and the direction for future research is clarified.