Wing motion of a dragonfly in the maneuvering flight, which was measured by Wang et al. [1]was investigated. Equations of motion for a maneuvering flight of an insect were derived. These equations were applied for an...Wing motion of a dragonfly in the maneuvering flight, which was measured by Wang et al. [1]was investigated. Equations of motion for a maneuvering flight of an insect were derived. These equations were applied for analyzing the maneuvering flight. Inertial forces and moments acting on a body and wings were estimated by using these equations and the measured motions of the body and the wings. The results indicated the following characteristics of this flight: (1)The phase difference in flapping motion between the two fore wings and two hind wings, and the phase difference between the flapping motion and the feathering motion of the four wings are equal to those in a steady forward flight with the maximum efficiency. (2)The camber change and the feathering motion were mainly controlled by muscles at the wing bases.展开更多
The use of passive mixing devices to enhance the mixing of supersonic streams is of importance in many aerospace and allied applications. A comparative experimental study of two such non-conventional axi-symmetric sup...The use of passive mixing devices to enhance the mixing of supersonic streams is of importance in many aerospace and allied applications. A comparative experimental study of two such non-conventional axi-symmetric supersonic nozzles for mixing augmentation is undertaken in the present study. The nozzles studied are conventional convergent divergent (c-d), ramp, and nozzle with secondary tabs at the Mach number of 1.7. The freejet characteristics of the jets from the nozzles and the confined mixing of the jets under isothermal and non-isothermal conditions were experimentally investigated. In addition, schlieren and laser light sheet methods are employed for flow visualization. Results of experiments on freejet showed rapid total pressure decay, higher jet width, and increased shear layer width in the case of jets from non-conventional nozzles. Also visualized were complex shock patterns in these jets. The confined mixing studies in both cold and hot flows confirm the increased mixing behavior of non-conventional nozzles within shorter mixing duct lengths. Laser sheet visualization clearly demonstrated the formation of streamwise vortices, which accounts for the enhanced mixing while employing the nozzles under study.展开更多
The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber In concentration gradient experiment, fixt...The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber In concentration gradient experiment, fixture was ignited from lean side. An experimental study was conducted in a combustion chamber. The combustion chamber has glass windows for optical measurements at any side. For the measurement of distribution of fuel concentration, infrared absorption method using 3.39μm He-Ne laser was used, and for the observation of propagating flame, Schlieren method was employed. As a measurement result of flame propagation velocity and flammable limit, for a mixture of an identical local equivalence ratio, flame propagation velocity in concentration gradient is faster than that in homogeneous mixture, and rich flammable limit in concentration gradient shows a tendency to be higher than that in homogeneous mixture.展开更多
文摘Wing motion of a dragonfly in the maneuvering flight, which was measured by Wang et al. [1]was investigated. Equations of motion for a maneuvering flight of an insect were derived. These equations were applied for analyzing the maneuvering flight. Inertial forces and moments acting on a body and wings were estimated by using these equations and the measured motions of the body and the wings. The results indicated the following characteristics of this flight: (1)The phase difference in flapping motion between the two fore wings and two hind wings, and the phase difference between the flapping motion and the feathering motion of the four wings are equal to those in a steady forward flight with the maximum efficiency. (2)The camber change and the feathering motion were mainly controlled by muscles at the wing bases.
文摘The use of passive mixing devices to enhance the mixing of supersonic streams is of importance in many aerospace and allied applications. A comparative experimental study of two such non-conventional axi-symmetric supersonic nozzles for mixing augmentation is undertaken in the present study. The nozzles studied are conventional convergent divergent (c-d), ramp, and nozzle with secondary tabs at the Mach number of 1.7. The freejet characteristics of the jets from the nozzles and the confined mixing of the jets under isothermal and non-isothermal conditions were experimentally investigated. In addition, schlieren and laser light sheet methods are employed for flow visualization. Results of experiments on freejet showed rapid total pressure decay, higher jet width, and increased shear layer width in the case of jets from non-conventional nozzles. Also visualized were complex shock patterns in these jets. The confined mixing studies in both cold and hot flows confirm the increased mixing behavior of non-conventional nozzles within shorter mixing duct lengths. Laser sheet visualization clearly demonstrated the formation of streamwise vortices, which accounts for the enhanced mixing while employing the nozzles under study.
文摘The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber In concentration gradient experiment, fixture was ignited from lean side. An experimental study was conducted in a combustion chamber. The combustion chamber has glass windows for optical measurements at any side. For the measurement of distribution of fuel concentration, infrared absorption method using 3.39μm He-Ne laser was used, and for the observation of propagating flame, Schlieren method was employed. As a measurement result of flame propagation velocity and flammable limit, for a mixture of an identical local equivalence ratio, flame propagation velocity in concentration gradient is faster than that in homogeneous mixture, and rich flammable limit in concentration gradient shows a tendency to be higher than that in homogeneous mixture.
