A special issue concerned in the current study is the supersonic ejector-based cooling system in an oil radiator air-cooled passage. To match the geometric feature of mixing chamber (variable sectional configuration with a big aspect ratio of cross section), a novel piccolo-tube multi-nozzles supersonic ejector is designed and numerically assessed. In the current 3-D numerical simulations, a simplified approach by utilizing an isotropic porous medium model is adopted for modeling the flow through a compact oil radiator. Simultaneously, a scaled-model experimental test is conducted for the purpose of validation. From a scaled-model test, it is suggested that the CFD simulation based on the porous medium approach is generally acceptable. In the presence of porous matrix, approximately 20%-40% decrease of the ejector pumping ratio is produced in relative to the situation without oil radiator, due to the flow resistance across the porous matrix. A conjunctive parameter considering the nozzle numbers, nozzle throat diameter, and piccolo-tube length is proposed. Either from the CFD-based analysis or from the scaled-model test, it is confirmed that there is an optimal conjunctive parameter for achieving the best ejector performance. (C) 2018 Elsevier Ltd. All rights reserved.