ICMAA Speakers
Prof. KHOO Boo Cheong
National University of Singapore, Singapore

Director, Teamsek Laboratories, National University of Singapore (NUS)

BC Khoo graduated from the University of Cambridge with a BA (Honours, 1st Class with Distinction). In 1984, he obtained his MEng from the NUS and followed by PhD from MIT in 1989. He joined NUS in 1989.

From 1998 to 1999, he was seconded to the Institute of High Performance Computing (IHPC, Singapore) and served as the deputy Director and Director of Research.

In 1999, BC returned to NUS and spent time at the SMA-I (Singapore MIT Alliance I) as the co-Chair of High Performance Computation for Engineered Systems Program till 2004. In the period 2005-2013, under the SMA-II, he was appointed as the co-Chair of Computational Engineering Program.

In 2011-2012, BC was appointed the Director of Research, Temasek Laboratories, NUS. Since 2012, he has been the Director, Temasek Laboratories.

BC Khoo serves on numerous organizing and advisory committees for International Conferences/Symposiums held in USA, China, India, Singapore, Taiwan, Malaysia, Indonesia and others. He is a member of the Steering Committee, HPC (High Performance Computing) Asia. He has received a Defence Technology Team Prize (1998, Singapore) and the prestigious Royal Aeronautical Prize (1980, UK). Among other numerous and academic and professional duties, he is the Associate Editor of Communications in Computational Physics (CiCP) and Advances in Applied Mathematics and Mechanics (AAMM), and is on the Editorial Board of American Journal of Heat and Mass Transfer, Ocean Systems Engineering (IJOSE), International Journal of Intelligent Unmanned Systems (IJIUS), The Open Mechanical Engineering Journal (OME) and The Open Ocean Engineering Journal.

In research, BC ‘s interest are in:
(i) Fluid-structure interaction
(ii) Underwater shock and bubble dynamics
(iii) Compressible/Incompressible multi-medium flow

He is the PI of numerous externally funded projects including those from the Defense agencies like ONR/ONR Global and MINDEF (Singapore) to simulate/study the dynamics of underwater explosion bubble(s), flow supercavitation and detonation physics. His work on water circulation and transport across the turbulent air-sea interface has received funding from the then BP International for predicting the effects of accidental chemical spills. Qatar NRF has funded study on internal sloshing coupled to external wave hydrodynamics of (large) LNG carrier.

BC has published over 360 international journal papers, and over 360 papers at international conferences/symposiums. He has presented at over 115 plenary/keynote/invited talks at international conferences/symposiums/meetings.

Speech Title: "Flow over shallow dimple arrays"

Dimple arrays have been successfully used for heat transfer enhancement because they increase the heat transfer at a relatively smaller penalty in terms of pressure losses compared to traditional heat transfer devices just as fins and pins (Moon et al. 2000, Chen et al. 2012). These usually involve relatively deep dimples with dimple depth to diameter ratios of more than 10% to generate the increased flow mixing for heat transfer enhancement. Some studies have also shown that arrays of dimples can also be used for drag reduction, and these typically involve very shallow round-edged dimples with depth to diameter ratios of 5% or less (Lienhart et al. 2008, Tay et al. 2015, van Nesselrooij et al. 2016). Maximum drag reduction obtained with such passive dimples are relatively small, with maximum drag reductions of about 5% for circular axisymmetric dimples.
Flow visualization experiments as well as numerical simulations have revealed the presence of streamwise vortices within the dimple as well as regions of flow separation at the upstream portion of such dimples (Ligrani et al. 2001, Isaev et al. 2002, Tay et al. 2014). The flow structure within the dimples as well as the size of the flow separation region was found to vary with the Reynolds number of the flow. This, together with the many parameters such as dimple depth to diameter ratio and the relative curvature at the dimple edge and within the dimple that affect the flow make the flow over the dimples relatively complicated to study (Mahmood and Ligrani 2002, Won et al. 2005, Tay et al. 2017). Nevertheless, having a better understanding of the flow mechanism causing the drag reduction would enable us to optimize the shape of the dimple and maximum the drag reduction obtained using such passive dimples. This is the main motivation of the present work on dimples.
Both experiments and numerical simulations have been carried out on shallow round-edged dimple arrays with dimple depth to diameter ratios of 5%. Pressure measurements have been carried out to quantify the drag reduction due to the dimple array in a turbulent channel flow for Reynolds numbers between 5,000 and 37,000, and hot-wire anemometry and Detached Eddy Simulations (DES) have been carried out to understand the flow over the dimples in greater detail. The study shows that the drag due to the dimple array reduces as the Reynolds number increases from 5,000 to 37,000. A drag increase is observed at Reynolds numbers below 13,000, while a drag reduction is observed above this Reynolds number. Similar streamwise vortices are observed with such shallow dimples as those observed in deeper dimples with depth to diameter ratios of 10% (Ligrani et al. 2001, Won et al. 2005). These streamwise vortices generate spanwise flow components near the dimple surface, resulting in reduced skin friction similar to those observed with traverse wall or flow motions (Iuso et al. 2002, Karniadakis et al. 2003). The flow is stabilized when drag reduction is present and shifts in the power spectra of the streamwise velocity signal as well as reductions of the peaks in the terms of the turbulence energy budget is observed with the drag reduction.
Although streamwise vortices are also present at lower Reynolds numbers, a drag increase is observed at lower Reynolds numbers, together with a relatively large flow separation region. The large flow separation region results in a large form drag at low Reynolds numbers. As the Reynolds number increases, the flow separation region shrinks, resulting in reduced form drag at higher Reynolds numbers.
The results show that while the streamwise vortices generating spanwise flow near the surface can reduce the skin friction drag, form drag present within the three-dimensional dimples can be significant enough that an increase is observed in the total drag. To optimize the dimple shape and maximize drag reduction, both the skin friction and form drag should be reduced. One possible method to reduce this form drag is through the use of asymmetric dimples, where the deepest point within the dimple is shifted backward, resulting in a shallower wall gradient at the upstream portion of the dimple. This has been shown to reduce the flow separation at the upstream portion of the dimples for deeper dimples with depth to diameter of 10% (Chen et al. 2012).

Prof. Xiaomin Wu
Tsinghua University, China

Dr. Xiaomin Wu is Professor of Energy and Power Engineering at The Tsinghua University, China. She received her B.S. and M.S. from The Dalian University of Technology (China) and Ph.D. from The Hiroshima University (Japan). After that, she had worked at The Penn State University (USA) as a Post-Doctoral Scholar for a few years and then joined The Tsinghua University. She served as Deputy Director of Institute of Engineering Thermophysics, and is Member of Expert Committee on High Efficiency Finned Tubes of China Nonferrous Metal Fabrication Industry Association, Member of Expert Committee of China National Chemical Energy Conservation (Waster Reduction) Center, and Member of Organizing Committee of China Refrigeration and Air-Conditioning Industry-University-Research Forum. She obtained many awards such as 2018 Wonderful Lesson of Innovation and Entrepreneurship Education in National Colleges and Universities of China, 2018 National Excellent Online Open Course of Ministry of Education of China, and 2018 and 2019 Excellent Doctoral Dissertation Instructors of Tsinghua University. Her research interests include: (1) heat and mass transfer, (2) heat transfer with phase change including frosting and defrosting, boiling and condensation, and aircraft icing, (3) surface wettability and interfacial transport phenomenon, (4) design and optimization of heat exchanger, and (5) water- and energy-conservation technologies. In the past three years, she has published 38 papers in various prestigious journals such as ACS Appl. Mater. Interfaces, Langmuir, Appl. Phys. Lett., Int. J. Heat Mass Transfer, Appl. Surf. Sci., and Appl. Therm. Eng.

Speech Title: "Supercooled water droplet freezing characteristics"

Freezing of supercooled water droplet is observed in many engineering and environmental processes. In aerospace, aircraft icing caused by supercooled droplet impinging greatly reduces the lift and increases the drag, constituting a huge threat to the aircraft flight safety. In the power sector, ice accretion on wind turbines or transmission lines may lead to a variety of problems. In meteorology, hailstorms may cause damage to buildings, crops, and automobiles. In refrigeration, frost formation on an evaporator increases the thermal resistance and blocks the airflow passage, resulting in a deteriorated thermal performance. In cryopreservation, water crystallization occurs during the food freezing process. Studies on freezing process of a supercooled water droplet can help us to better understand the ice/frost formation and accumulation. We have recently conducted a series of studies on supercooled water droplet freezing and obtained many interesting results, the present talk introduces some of them, which include the icing nucleation characteristics of sessile water droplets, shape variation and unique tip formation of a sessile water droplet during freezing, droplet impacting and freezing behaviors, etc.

Prof. Jia-Yush Yen
National Taiwan University, Taiwan

Professor Jia-Yush Yen received the B.S. degree from National Tsing-Hwa University, Taiwan in 1980, the M.Sc. degree from University of Minnesota, USA, in 1983, and the Ph.D degree from University of California, Berkeley in 1989, all in mechanical engineering. He then joined the Mechanical Engineering faculty of National Taiwan University where he served as the Department Chair, the director of Tjing-Ling Industrial Research Institute, and the Dean of the College of Engineering until 2017.

Prof. Yen served as the Chair of the Automation Area for the National Science Council, the president of the Chinese Institute of Automation Engineers (CIAE) for four years. He is a fellow of the ASME, Chinese Society of Mechanical Eng., and CIAE. Dr. Yen received many awards, among them twice the Outstanding Research Award from Taiwan National Science Council (now the Ministry of Science and Technology) is awarded only to the topmost researchers in their area. Dr. Yen also received numerous complements from the government for his public service. He had also served as consultant for many companies and institutes. His research interests are in the areas of mechatronic systems, computer peripherals, and nano-manipulations.

Speech Title: "Diagnosis of Keratoconus Based on Corneal Dynamic Response"

Modern non-contact tonometer achieves the applanation required for intraocular pressure measurement by shooting a very rapid air-puff onto the cornea. The rapid air-puff offers more comfortable testing process, but it also induces undesirable wave propagation along the corneal surface. It is our desire to make use of this wave propagation signal for the detection of possible intraocular pressure (IOP) related diseases. We first show that with the applanation geometry is affected by the IOP. We then explain how the wave propagation is related to the IOP. With the mathematical description of the corneal wave propagation, we noticed that the decomposed responses are different between normal human eye and the eye that suffers from keratoconus. With the proper analysis, we propose an analysis tool for detecting possible keratoconus with the dynamic response measured by an air puff response recorder with Scheimpflug imaging.

Accepted abstract & Full paper will be invited to give the presentation at ICMAA 2020