Research On Enhancing Flow Mixing Based On Air Tabs

The airtab is a new technique to enhance the flow mixing. It has a better effect and less energy loss compared with the conventional ejector. In order to determine the mixing effect and application prospect in different conditions, this paper studies convergent nozzle, turbofan jet and Rocket Based Combined Cycle(RBCC) exhaust system with airtabs. And the influence to the fluid structure and the mixing efficiency by the parameters of the airtabs is studied deeply. In this paper, the flow field structure and nozzle performance under different operating conditions and airtabs' parameters are studied by the way of numerical simulation and wind tunnel test.First of all, a wind tunnel experiment is carried out to determine the influence of the number and inlet total pressure of airtabs by measuring the total pressure distribution in the core area of the nozzle jet. Numerical simulation is carried out for the experimental conditions. And the numerical simulation results are in good agreement with the experimental results. The accuracy and reliability of the method are verified. Experimental and numerical simulation results show that when the number of the airtabs is 6, the length of the jet core region is the shortest, and the length is 3.2D. The higher the total pressure of the airtabs is, the shorter the core area of the jet is and the better the mixing efficiency is.Then the application of air tabs in the by-pass turbofan nozzle mixing is studied by using the numerical simulation method. The variation of the nozzle vorticity field, thermal mixing efficiency, total pressure recovery coefficient and thrust coefficient are obtained when the number and position of the air tabs varied. The numerical simulation results show that when the total flow rate of the gas is fixed, the less the airtabs is, the higher the thermal mixing efficiency is. When the number of air tabs is 2, the thermal mixing efficiency is 0.278, which is improved by 65% compared with the reference nozzle. In addition, if the position of air tabs is closer to the intersection of the core and the fan, the thermal mixing efficiency is higher. The variation of total pressure loss at various operating conditions is less than 0.1% compared with reference nozzle and it can be neglected.Considering the flux of air tabs should be as small as possible, this paper studies the method to decrease the flux of air tabs under the premise of ensuring the mixing efficiency, and that is the unsteady air tabs.In this paper, two kinds of unsteady air tabs are study, one is to keep the number of the air tabs constant, but the inlet total pressure of air tabs changes periodically. The other is to increase the number of air tabs to 2 times, and work alternatively. And the influence of period on mixing efficiency and performance of nozzle is studied and the application scenarios of these two methods are determined. The first scheme can effectively reduce the flow rate of air tabs, and the second can get the best mixing efficiency in the condition of constant flow rate of air tabs.At last, the paper explores the mixing of the RBCC with air tabs in ejector mode. The results show that the RBCC can enhance the mixing effect of primary and secondary flow, but it may cause the decrease of the flow rate and thrust performance.