Session: 36-04 Water, Icing, and Lubricant Deposition

Paper Number: 79505

79505 - Droplet Impact on a Curved Moving Liquid Film 

The European Commission has set a target to reduce the emissions of CO2 and NOx by 75% and 90%, respectively per passenger per kilometre by 2050. To achieve these goals there is a need to develop more efficient engines. Computational modelling of elements within the aero-engine will play a key role in achieving this goal. One important part of the aero-engine transmission system is the bearing chambers, which house the bearings that locate and support the shafts. The flow inside a bearing chamber is a complex two-phase flow with droplets impacting on the moving films along the curved walls. Currently, the computational models used to characterise impact outcomes from these splashed droplets are based on correlations obtained for droplet impacts on plane films. The present study aims to bridge that gap by investigating droplet impact on a curved moving film. 

Experiments were conducted on a curved surface having major and minor radii of 1000 mm and 400 mm, respectively. The variation in the channel curvature provided the opportunities to investigate the droplet impact at three different curvatures. Two droplet diameters of 2.3 mm and 1.9 mm were obtained using two different needles sizes. The height of the syringe from the liquid film was varied to investigate the effect of droplet impact velocity. Four flow rates were considered to investigate the effect of film thickness on droplet impact. The working fluid used in the present study is water. To investigate the dynamics of the droplet impact, a high-speed imaging technique was used. 

Qualitatively, two different impingement outcomes were observed, namely, crown formation and crown splashing. The key difference between the two outcomes is in the production of secondary droplets from the crown in crown splashing. Similar to droplet impact on an angled film it was observed that at a high angle of impingement the resulting crown formation is skewed to the downstream side, while at low angles of impingement, the crown formation is fairly symmetrical. The reason for the skewness can be attributed to the difference between tangential velocity of the droplet and the velocity of the film. 

Quantitatively, it was observed that at low angles of impingement, the transition from crown formation to crown splashing agrees strongly with previous literature for impact on static films and films on an angled plane where the transition value of the splashing parameter is 2100 based on the absolute velocity of the droplet. At angles of impingement higher than 40°, the critical splashing parameter value was found to increase. The present study shows that the transition from crown formation to splashing at different curvatures is identical to that of inclined planes at similar angles. 

The duration of an impact event was also investigated, defined as the time for which disturbance waves from the impact persist. The study shows that there is an upper limit to the time of impact, beyond which increasing the impact energy does not increase the duration of the waves.

Presenting Author: AVICK SINHA Gas Turbine and Transmissions Research Centre

Presenting Author Biography: Dr. Avick Sinha is a Research Fellow in the Gas Turbine Transmission Research Centre (G2TRC) at the University of Nottingham. He has expertise in multiphase flows &amp; free shear flows with 5+ years of experience in experiments and numerical modelling. He is currently working on the oil flow characteristics in the aero-engine bearing chamber and gas-sheared flows in partnership with Rolls-Royce. His current research is involved in curtailing the carbon footprint and increase the efficiency of aero-engine. <br/><br/>He received his PhD degree from IIT Bombay, India. He was a recipient of the prestigious Prime MInsiter&#39;s Fellowship during his PhD. His PhD work is done in collaboration with General Electric and TBRL, India. <br/><br/>During the course of his research career, he has published several peer-reviewed papers and also won awards for his research work. He has collaborated with both industrial and academic settings​.

Authors:

AVICK SINHA Gas Turbine and Transmissions Research Centre
Vaibhav Ramakrishnan The University of Nottingham, UK
Kathy Johnson The University of Nottingham, UK