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Experimental and Computational Investigation on ... · PDF fileExperimental and Computational Investigation on Interaction between Nano Rotor and Aerodynamic Rudder ... and minimum

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  • Experimental and Computational Investigation onInteraction between Nano Rotor and Aerodynamic

    RudderD. YANG, Z. LIU, C. BU

    State Key Laboratory for Strength and Vibration of Mechanical Structures, school of Aerospace Xian Jiaotong University,Xian, China

    ABSTRACT

    The interference effect between the nano rotorand aerodynamic rudder was studied experimen-tally and computationally. Propulsive perfor-mance of nano rotor and aerodynamic perfor-mance of aerodynamic rudder were achieved ex-perimentally. The disturbed flow field of nanorotor was also analyzed computationally to dis-close the flow mechanics of the interaction. Re-sults showed that the nano rotor has a great effecton the aerodynamic performance of aerodynam-ic rudder. The moment of aerodynamic rudderfluctuated with the rotor-to-rudder spacing andachieved the smallest value at the spacing of 0.5R. And the moment of aerodynamic rudder var-ied with deflection angle linearly. Aerodynamicrudder influenced the propulsion performance ofthe nanor rotor slightly. The thrust coefficientand torque coefficient increased a little with s-pacing but changed slightly with the deflectionangle. Numerical simulation showed that aero-dynamic rudder blocked the flow field of thenano rotor and the counter-clockwise rotation ofthe rotor drives the flow in the downstream ro-tating in a counterclockwise direction resultingin the different angle of attack between left andright rudder surface.

    1 INTRODUCTIONAerodynamic rudder is one of the useful methods to con-

    trol the attitude of rotary-wing nano air vehicle (NAV) dueto the limitation of its size and weight [1][2]. The inter-action between nano rotor and aerodynamic rudder inducescomplex flow phenomenon and influences the performance ofboth nano rotor and rudder. Therefore, it is necessary to studythe interference effect and disclose the inherit flow mechanicsso as to design nano rotor and rudder with high performance.

    Nano rotor is characterized by small size and low rota-tional velocity causing that its operational Reynolds numberis very low which is usually below 2.0104 or less. At low

    Email address: liuz@mail.xjtu.edu.cn

    Reynolds number, it is laminar flow and unstable. Due to theweak inertia force in the boundary layer, strong adverse pres-sure gradient appears at the maximum suction point of theleading edge. As a result, the flow separates from blade sur-face and wake vortices generate. The vortices interact withrudder resulting in the change of control efficiency of rudder.On the contrary, the rudder in the wake flow blocks the wakeflow of the nano rotor and influences the propulsion perfor-mance of nano rotor.

    The interference effect between propeller and wing is wellstudied . Fratello et al. [3] investigated the mutual interfer-ence of large propeller and wing using wind tunnel and liftingsurface method. Results showed that the drag coefficient ofthe wing increased while the lift coefficient of the wing de-creased. On the other hand, both the thrust coefficient andpower coefficient of the propeller increased. Moens et al. [4]used the actuator disk model to replace the propeller. And theinterference effect between the slipstream of propeller andwing was studied using Navier-Stokes solver. Gamble [5]tested the interaction between a micro propeller and a wingin the wind tunnel and it was found that 12% to 18% thrustof the propeller transformed to the drag of the wing. Hu et al.[6] studied the influence of the rudder to the wake flow of pro-peller. Potential flow method was used to establish the inte-grated formulation of the strength of doublet at the surface ofpropeller blade. As the induced flow velocity was solved, theinfluence of the rudder to the propeller was detected. Wang etal. [7] employed Reynolds average N-S equations to establishthe interference model of propeller to rudder. Results showedthat the propulsion performance of the front propeller was notsensitive to the horizontal and vertical position of the rudder.Yang et al. [8] used the lifting surface method to study therudder performance in the wake flow of propeller. Duan etal. [9] analyzed the influence of propeller slipstream to theaerodynamic performance of the wing at different angles ofattack using the sliding mesh technique. And results showedthat the thrust of propeller changed as the result of wing andthe lift of wing increased at high angle of attack because ofthe influence of propeller.

    In summary, the experimental and numerical methods aremainly employed to study the mutual interference effect be-tween the rotor or propeller and the wing. These researchesprovide the study of interference of nano rotor and aerody-

    1

  • namic rudder with some references. However, the interfer-ence effect between rotor and rudder is scarcely studied be-cause most of research focuses on the aerodynamic interac-tion between propeller and wing. As the aerodynamic rud-der operates at different deflection angles, it has a high im-pact on the propulsion performance of rotor, especially at thehigh deflection angle. Therefore, it is necessary to investi-gate the mutual interference between rotor and rudder. Fur-thermore, most of the researches above studied the interac-tion at high Reynolds number. It shall be pointed out thatthe rotary-wing NAV operates at an ultra-low Reynolds num-ber. At ultra-low Reynolds number, the phenomenon, that islaminar separation and laminar separation bubble, appear dueto the adverse pressure gradient in the boundary layer, whichresults in the unsteady non-linear aerodynamic characteris-tics for flight vehicles [10]. In this paper, the mutual inter-ference effects between nano rotor and aerodynamic rudderat ultra-low Reynolds were therefore studied experimentallyand numerically. The influence of rudder deflection angle androtor-to-rudder spacing to nano rotor propulsion performanceand aerodynamic rudder aerodynamic performance was in-vestigated. And the interfered flow field of nano rotor wasstudied to find out the radical reason for the variation of rotorperformance. It is believed that the research will provide thedesign of rotary-wing NAV with a reference.

    2 EXPERIMENTAL SETUP2.1 Nano rotor and Aerodynamic rudder

    Conventional helicopter rotor typically has uniformchord. It controls attitude and fight direction through collec-tive and cyclic pitch control. Because small MAVs are char-acterized by extremely small size and weight, conventionalcontrols are not feasible. Therefore, rotor blades with twistedand non uniform chord are particularly attractive for propul-sion optimization. Thus a nano rotor with diameters of 7.5 cmwas designed based on low Reynolds number aerodynamicsand minimum induced loss theory to minimize energy loss.The blade airfoil has 2% thickness with 5% curvature circu-lar arc. The rotor has a mean chord of 0.33R and mean twistangle of 17.21 as shown in Figure 1. The geometry of nanorotor is shown in Figure 2. After obtaining chord length andtwist angle distribution, the nano rotor was fabricated withcarbon laminar and epoxy resin.

    To control the attitude of rotary-wing NAV, an aerody-namic rudder system is installed in the wake flow of nanorotor. The aerodynamic rudder system includes two pieces ofrudder as shown in Figure 3. Each piece of rudder is a rectan-gle flat plate whose the long edge is 0.8 R long and the shortedge is 0.53 R long. Here R represents the radius of nanorotor. To avoid the influence of motor and increase the con-trol efficiency of aerodynamic rudder, a horizontal spacing of0.4 R exists between two pieces of rudder. The rudder wasfabricated with carbon laminar and epoxy resin as well witha thickness of 0.3mm.

    Figure 1: Blades chord and twist distribution of nano rotor.

    Figure 2: Schematic of of nano rotor.

    2.2 Interference Effect Test BenchAn interference effect test bench was designed to measure

    the thrust and torque of nano rotor and the control momen-t and force of rudder due to interference effect as shown inFigure 4. The test bench was composed of aerodynamic rud-der test part, nano rotor test part, energy supply system andthe data acquisition system.

    The rudder system consists of the aerodynamic rudder, asmall servo, a control panel, a 6-DOF balance band a supportbeam. The aerodynamic rudder was assembled horizontallywith a support beam under the wake flow of nano rotor. Thesupport beam was fixed on the small servo by which the rud-der can change its deflection angle accurately. The controlcommand was generated by the computer. Then it was trans-ferred to the servo by virtual of control panel typed ArduinoMega,ATmega1280. The 6-DOF balance is a ATI nano 17(Ti) balance with a maximum force capacity of 14.1 N and amaximum moment capacity of 50 Nmm. The aerodynamic

  • Figure 3: Schematic of aerodynamic rudder.

    force and moment can then be measured with the balance.The nano rotor test part consists of the nano rotor, speed

    controller, a torque sensor, a load cell, a support beam. Inorder to establish the pure torque of the rotor, an ultra-low-capacity static torque sensor DH15 by the SCAIME companywith a capacity of 0.005 Nm and an accuracy class of 0.1%was used to measure the torque. In addition, the load cellfor measuring the thrust was a load cell Honeywell Model31 with a capacity of 2.0 N. The torque cell was installed onthe load cell directly. And an extended supporting beam wasinstalled vertically supporting the motor and rotor to avoidthe effect of the torque. The controller was YGE4-BL forbrushless motors. The speed control command generated bycomputer was transferred to speed controller with which therotational speed of nano rotor can be adjusted.

    The energy supply system is a regulated DC power sup-ply, which can adjust the voltage and stabilize it at a certainvalue to provide micro motor and servo with current.

    T

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