Study on Cruise Drag Characteristics of Low Drag Normal Layout Civil Aircraft

This paper focus on the wing shape related drag reduction measures of normal layout civil aircraft, through the drag reduction to improve the aircraft performance. Mainly by the laminar flow wing to reduce skin drag and weak shock wave wing to reduce shock drag, to keep a section of laminar zone on the wing leading edge to reduce skin drag, the wing profile's pressure distribution transit from the middle part's tonsure pressure zone to the trailing edge's inverse pressure gradient zone gentle to reduce the shock drag. The wing body junction plus the body belly fairing to increase the junction flow velocity, through increase flow velocity to weak the boundary layer stacked at the junction, improve the drag performance. The blended winglet to reduce the wing tip induced drag, study the shape parameters impact on the drag reduction, longitudinal moment and directional moment, attain the winglet model with drag reduction effect, suitable pitching moment and directional moment. For the wing body fairing have significant impact on the wing shape lower surface pressure distribution, the winglet have important impact on the wing tip flow, so the single part drag reduction measure is not feasible, need to carry out integrated drag reduction study on the wing related three drag reduction measures, and study the drag reduction measure's drag reduction decrement, put a reference for the normal layout civil aircraft's drag reduction. Through the above drag reduction measure's assessment attain the effect of drag reduction and rising the normal layout civil aircraft's cruise ratio, improving the cruise performance.

Experimental analyses of synthetic jet control effects on aerodynamic characteristics of helicopter rotor

ABSTRACTExperimental analyses of synthetic jet control (SJC) effects on aerodynamic characteristics of rotor in steady state and in hover were conducted. To ensure the structural strength of rotor and enough interior space for holding the synthetic jet actuators (SJAs), a particular blade with a frame-covering structure was designed and processed, and the experiment was conducted with low free stream velocities and rotor rotation speeds. There were three test conditions. In steady state, there were three free stream velocities (10m/s, 15m/s and 20m/s). In hover state, the rotor was worked with two rotation speeds of 180RPM and 240RPM. In forward flight, the rotor was worked with a rotation speed of 180RPM and a free stream velocity of 7.5m/s. To measure the synthetic jet control effect on rotor in stall, the range of collective pitch was set from 10° to 28° in steady state. The aerodynamic forces and sectional velocity field were measured by using the six-component balance and the Particle Image Velocimetry (PIV) system in the wind tunnel. Flow control effects on the blade based on the synthetic jets (SJ) were experimentally investigated with different jet parameters, such as jet locations, jet angles, and jet velocities. In steady state, the jet closer to the leading edge, and the jet angle of 90° had more advantages in improving the aerodynamic characteristics. Furthermore, the aerodynamic forces and sectional velocity field measurement of rotor in hover were conducted, it showed that SJAs could increase flow velocity at the upper surface, which led to lower upper surface pressure. As a result, the normal forces of rotor with two rotation speeds were increased significantly. These results indicated that the synthetic jet has a capability of increasing the normal force and delaying or preventing the stall of rotor.

Enhancing Output Power of a Cantilever-Based Flapping Airflow Energy Harvester Using External Mechanical Interventions

This paper presents a flapping airflow energy harvester based on oscillations of a horizontal cantilever beam facing the direction of airflow. A wing is attached to the free end of a cantilever beam and a bluff body is placed in front of the wing from where vortex falls off, producing vortices under the wing and driving it to oscillate. An electromagnetic transducer is integrated to convert the flow induced vibration into electrical energy. This flapping energy harvester, however, may stop oscillating or vibrate in the second mode under high electrical damping, and thus may be unable to achieve its optimum performance. Simple yet effective mechanical interventions can be applied to the harvester to enhance its power output, i.e., to increase flow velocity and to apply external magnetic interaction. The effect of airflow velocities on output power was investigated experimentally and the results show that the energy harvester scavenges more power in airflow at higher Reynolds numbers (higher flow velocity at R e < 24,000). The external magnetic excitation is achieved though placing one magnet to the wing and another one above the wing to induce a repelling force, aiding the beam to oscillate in high electrical damping. Experimental results show that the power output can be enhanced by 30% when the magnet interaction is properly integrated.

The Effects of Flushing on Water Quality and Biofilm Biomass in Different Daily Flow Patterns of Distribution System

We studied the effects of flushing on water quality and biofilm biomass in different daily flow patterns of distribution system. After building up steady biofilm layers in two flow velocity (0.25 m/s and 0.65 m/s) distribution systems consisting of PE pipe, then flushed by stepwise increased flow velocity. An increase flow velocity caused an immediate increase in turbidity and heterotrophic bacteria of water as a result of detachment of biofilms in the pipes, especially in low flow patterns distribution system. Three days later after flushing, water quality of two systems were generally lower and more stable than before flushing. Flushing strategies only limited biofilm growth to a certain extent and did not completely eliminate microorganisms from the systems.The low flow velocity distribution system was easily being disturbed by flushing.

Thrust Characterization for Bio-Inspired Pulsatile Vortex Ring Thrusters With Variable Exit Nozzle Diameter

The thrust response of a bio-inspired pulsatile vortex ring thruster is explored for variable diameter exit nozzle profiles. Our pulsatile vortex ring thruster is composed of a plunger in a submerged cavity that oscillates to intake and expel fluid through an exit nozzle creating vortex rings which generate thrust. The diameter of the exit nozzle is expanded upon fluid intake to increase volume flow. Upon fluid expulsion the nozzle diameter is reduced to increase flow velocity. This allows for an increase in total thrust. The effect is a thrusting force from a positive net flux in momentum with a zero net flux in mass. This is loosely inspired by jellyfish which utilize the same orifice for both mass intake and expulsion. The thrust is directly measured for multiple diameter profiles. A selected diameter profile is either a constant exit nozzle diameter or a sinusoidal oscillation of exit nozzle diameter that corresponds to the plunger motion. The increase in thrust is analyzed with respect to variable diameter effects and compared to thrust results of constant exit diameter nozzles.