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摘要
The focus of present numerical study is on assessment of control of laminar separation bubble phenomenon using Micro-scale combustion actuators in an airfoil with low Reynolds number under surface effect and free flows. In this way, the characteristics of laminar separation bubble such as its formation, geometry, and transition from laminar to turbulent around airfoil SD8020 in attack angles of 5 and 8 are investigated. Following that, the new combustion actuators in Micro-scale, cold, and hot air-jet injection are introduced to control boundary layer flow in terms of eliminating the separation bubble. Some mechanisms are identified for improvement of methane-air premixed flame stabilization in a Micro-scale combustor, which includes effects of added hydrogen to methane as an additive, a central conductive wire insertion, and creating steps in the reactor. The finite volume method is used to solve the turbulent unsteady flow equations. The results are compared with experimental and numerical data obtained by other researchers and show good conformity for aerodynamic coefficient predicting. The SIMPLE-C method is used in numerical algorithm utilized to coupling pressure and velocity fields, the second order upwind method is used to discretization of momentum equation, and finally SST Transient k-omega equations is used for turbulent flow modeling. The results show that the selected numerical method is able to recognize reverse pressure gradient, laminar separation bubble, and flow transition from laminar to turbulent in boundary layer. The bubble formation location and flow transition are also inclined towards airfoil leading edge under surface effect, and pressure distribution makes a variation in laminar separation bubble formation location. The utilization of combustion actuators leads to a decrease in flow Reynolds number along with airfoil wall and a tendency of flow to relaminarization. This causes a larger increase in the lift coefficient than the hot-air-jet injection. But additionally the friction effects on the surface is increased by laminar flow, that leads to an increase in friction drag coefficient of reacting jet rather than the hot-air jet and generally an increase in drag coefficient. On the other hand, the stall phenomenon control by combustion actuator also leads to an increase in stall angle limit from 10 to 14, and lift coefficient improvement to 26% than without jet injection, through flow separation delay.
- 出版日期2016-12-21
