Abstract: Based on three dimensional CFD of the lobed mixer-ejector,the effects of lobe nozzle geometric parameters on the lobed mixer-ejector performance were revealed.The results show that the increase of lobe width causes the rapid decrease of ejection ratio.The velocity circulation at lobe exit section and the thermal mixing efficiency decrease with the increase of lobe width,whereas the pressure recovery coefficient is improved by the increase of lobe width.The effect of lobe diffusion angle on the ejection ratio depends on the mixing duct diameter.For the case of small diameter mixing duct,the ejection ratio increases firstly and then decreases with the increase of lobe diffusion angle from 20 degrees to 90 degrees.For the case of large diameter mixing duct,the ejection ratio increases continuously with the increase of lobe diffusion angle.The increase of lobe diffusion angle results in the increase of velocity circulation at the lobe exit section,but it raises the mixing loss and lowers the pressure recovery coefficient.