Transient Boundary Layers
Boundary layer flows in internal combustion engines (important to understand for heat transfer predictions) behave quite differently from steady boundary layers since external flow, temperature, and pressure continuously change and do not permit the development of a well-established boundary layer flow. Detailed insights into the transient nature of such flows in engines have been comprised for a long time due to limitations in experimental techniques. High-frame-rate laser based imaging tools have been developed and now allow in-depth studies that support the development of advanced and truly predictive simulation tools.
The experimental work in our lab was the foundation for the development of a new heat transfer model in collaboration with Prof. Matthias Ihme (Stanford):
Ma, P. C., Ewan, T., Jainski, C., Lu, L., Dreizler, A., Sick, V. and Ihme, M., "Development and Analysis of Wall Models for Internal Combustion Engine Simulations Using High-speed Micro-PIV Measurements," Flow Turbulence and Combustion 98, 283–309 (2017) 10.1007/s10494-016-9734-5
Ma, P. C., Greene, M., Sick, V. and Ihme, M., "Non-equilibrium wall-modeling for internal combustion engine simulations with wall heat transfer," International Journal of Engine Research 18 (1-2) (2017) 10.1177/1468087416686699
Flow field imaging example
Planar laser induced fluorescence can visualize local temperature differences
Temperature inhomogeneities are significantly higher near the cylinder head than in the bulk gas. Substantial changes during an engine cycle are observed.