Research On Helicopter Circulation Control Tail Boom Anti-torque System

Though Circulation Control Tail-Boom Anti-Torque System(CCTAS) performs better than normal tail rotor in many aspects, it still has not been widely used due to its larger power consumption. As an important part of CCTAS, the circulation control tail boom, which acts as an aerodynamic part by blowing a thin flow out of each slot to guide the attached rotor down wash flow in order to generate side force to cancel the rotor anti-torque, has the potential to be optimized to reduce power consumption of the whole anti-Torque system. With the purpose of reducing power consumption, a theory analysis model of circulation control tail boom is established. By using the analysis model, lift related parameter analysis on slots, and geometry of the slots and tail boom cross section is accomplished systematically. Based on the analysis result, schemes of adjusting the slot width and velocity of the slot jet during flight according to velocity of the down wash flow are proposed, and the related mechanisms are designed. In order to validate the analysis conclusion and verify the in flight adjusting schemes and mechanisms, an anti-torque test rig including a CCTAS test platform is designed and manufactured, and a test is accomplished with the test platform.As background of this paper, advantages and disadvantages, present situation of the research, deficiency and difficulty of China and abroad are discussed at first, research content and its method is then proposed.Based on CFD method, a theory analysis model is established using N-S govern equations and realizable turbulence model. In order to take the effect of the slots into account, the computational grid includes the inner part of the tail boom. The comparison between the test result shows that the analysis model has a relatively high accuracy, so that it could be used for the analysis of the circulation control tail boom.By using this simulation method, a parameter analysis is completed systemically. The analyzed parameters includes working parameters of the tail boom(down wash flow velocity, jet flow velocity, slot attack angle, et.al), geometry parameters of the slots(geometry of the slots and value of different geometry parameters), and geometry of the tail boom cross sections. The result shows that lift can be increased and stability of the attached flow could be enhanced by increasing velocity of the jet flow, or decrease the blow angle, or increase diameter of the cross section of the tail boom, or utilizes two slots instead of one. With the purpose of increasing jet velocity or decreasing blow angle, 6 different shapes of slots are designed, analyzed and compared to each other. The result shows that arc-profiled slot performs best because that its blow angle is close to 0°, and it is helpful for increasing jet flow velocity, and most importantly the jet flow and attached down wash flow do not flow separately. The analysis on the tail boom cross section shows that increasing down wash flow velocity, or decrease blow angle is helpful for optimizing the shape of tail boom cross section so that non-circular cross section produce larger lift. Actually, the true importance of non-circular cross section to tail boom is that it inhibits the flows keeping attached on surface for cycles(called “over blown effect”). Small down wash velocity during helicopter routine flight makes “over blown effect” easily take place, which makes CCTAS generate smaller lift with more power consumption.To make the research more practical, a helicopter referenced to MD 520 N is virtually created. Down wash velocities and anti-torques of helicopter different flight states are computed to improve the slot width, jet velocity, and geometry of tail boom cross section accordingly. The optimization result shows that jet flow velocities which make maximum moment around the main rotor shaft are different according to different down wash flow velocities. In flight adjusting schemes and mechanisms to adjust jet flow velocity, slot width, slot length and slot longitude location according to velocities and range of the down wash flow are also proposed and designed respectively.At last, an anti-torque test rig including a CCTAS test platform is designed, and manufactured. A test is also accomplished with the CCTAS test platform and a wind tunnel simulating down wash flow. The test validated some of the conclusions summarized from CFD simulations such as best slot attack angle varies to other parameters and slot width larger than critical value decreases the lift, and so on. The test also verified the feasibility of the in flight adjusting schemes and effectiveness of their mechanisms.