City University of London. This research activity, involving Dr. Ligrani, is in collaboration with Dr. Qiang Zhang, and associated graduate students, of the City University of London. Previous experiments recognize that substantial heat transfer augmentation is achieved by adding ribbed turbulators after jet impingement with cross flow present. The present study investigates the fundamental working mechanism in a typical turbulent channel flow. Conjugate CFD simulations are employed for ribs, jet impingement, and their combinations. Flow characteristics and drawbacks for the individual and combined enhancement techniques are highlighted. New analysis on the coupled design arrangement reveals that the counter-rotating vortices generated by the jet flow can energize inter-rib recirculating vortices and promote spanwise convection. With an optimal design combination arrangement, extra heat transfer benefit is achieved beyond that associated with simple superposition of rib and jet impingement techniques. As such, the resulting thermal design approach is confirmed using published experimental data, and thus, is useful for surface heat transfer augmentation optimization in practice. Also of interest are the effects of coolant and wall temperature variations on impingement jet array thermal performance.

REFERENCES
Secondary Flows and Extra Heat Transfer Enhancement of Ribbed Surfaces With Jet Impingement (Z. Wang, Q. Zhang, Y. Yan, K. Liu, and P. M. Ligrani) Numerical Heat Transfer, Part A: Applications, Vol. 72, No. 9, pp. 669-680, November 2017.

Effects of Coolant and Wall Temperature Variations on Impingement Jet Array Thermal Performance (S. Lu, Q. Deng, P. M. Ligrani, H. Jiang, Q. Zhang), Numerical Heat Transfer, Part A; Applications, Vol. 79, No. 1, pp. 68-82, January 2021.