The present paper predicts the induced drag in the ground effect using wake surface integration. The total drag can be decomposed into physical drag components such as wave, profile, and induced drag. First, we confirmed that applying wake surface integration to cases of ground effect is theoretically valid as long as a moving boundary condition is implemented for the ground surface. Second, total drag comparison between body surface integration and wake surface integration is performed to numerically identify the disparity. Last, the induced drag component is extracted at various heights. In addition, endplates are mounted on wing tips to determine their impact on the ground effect. This study uses the Navier-Stokes solver for aerodynamic analysis, and a Clark-Y wing with DHMTU concept is generated. As a result, the wake surface integration satisfactorily shows the characteristics of the induced drag in the ground effect with the Clark-Y wing and wing-endplate combinations.
A three-dimensional computation was conducted to understand effects of low Reynolds numbers on loss characteristics in a transonic axial compressor, Rotor 67. As a gas turbine becomes smaller and it operates at high altitude, the engine frequently operates under low Reynolds number conditions. This study found that large viscosity significantly affects the location and intensity of the passage shock, which moves toward the leading edge and has decreased intensity at low Reynolds number. This change greatly affects performance as well as internal flows, such as pressure distribution on the blade surface, tip leakage flow and separation. The total pressure ratio and adiabatic efficiency both decreased by about 3% with decreasing Reynolds number. At detailed analysis, the total pressure loss was subdivided into four loss categories such as profile loss, tip leakage loss, endwall loss and shock loss.
Flow quantities in the hot and cold flow conditions of a turbine cascade were compared at the same exit isentropic Mach and Reynolds numbers by three-dimensional flow simulations. In the hot flow condition, the total temperature at the inlet was 772 K, and the isothermal temperature of the blade was 540 K. In the cold flow condition, the total temperature at the inlet was 280 K, and the blade was adiabatic. As a result, the cold and hot flow conditions were similar in total and static density in the wake, total and static pressure, velocity, the thicknesses of the viscous and thermal boundary layers, and the amplitude and frequency of the vortex shedding. On the other hand, they were different in static density in the boundary layer, and total and static temperatures. Moreover, the Eckert-Weise effect was observed in the cold flow condition, while energy separation in the wake was observed in the hot flow condition.
This paper describes the dynamic modeling and analysis of a fixed-wing micro air vehicle (MAV). A nonlinear model for the MAV motion with six degrees of freedom is formulated first. Next, an extended version of the linear-time-invariant model for the MAV is derived by applying small perturbation theory and linearizing around an equilibrium flight condition. This ad hoc extended model for the MAV retains more terms that are generally neglected in mathematic models of conventional airplanes. To explore the stability and control characteristics, the aerodynamic derivatives required by dynamic modeling are evaluated using low-Reynolds-number wind tunnel testing data and some theoretical/empirical formulas. A fixed-wing MAV with a 15-cm wingspan successfully flown in 2002 is used as a baseline prototype for dynamic modeling and analysis. The longitudinal and lateral dynamic responses of the MAV under various conditions are demonstrated. The performance of the present extended MAV model is investigated by comparing the flight dynamics for different models. The simulation results show that the proposed extended model is consistent with the nonlinear dynamics model for a wider range of flight conditions. The present analysis may aid a better understanding of flight characteristics as well as design and analysis of MAV systems.
Endo et al. (2004) applied thermodynamic analysis to a simplified Pulse Detonation Turbine Engine (PDTE) system to estimate ideal performance; the theoretical thermal efficiency of a non-compressor type PDTE system is assumed to be 20% to 30% with an ethylene-oxygen mixture. Several experimental studies were conducted using a test apparatus composed of an automobile turbocharger connected to a single-tube pulse detonation engine (PDE). The results demonstrated that the measured thermal efficiency was 1% to 5%, far lower than the theoretical thermal efficiency. These studies covered the simplest PDTE system, in which the detonation wave from a PDE tube is directly incident to a turbine and can be considered as the lowest PDTE system performance. This study clarifies the reduced thermal efficiency by building a model simulating the inside of a turbine. The relationship between the turbine peripheral velocity and thermal efficiency of a non-compressor type PDTE with an ethylene-oxygen mixture was determined based on the premise of being constant turbine peripheral velocity during one PDE cycle. The PDTE test apparatus with a single-tube PDE connected automobile turbocharger was used to verify this model experimentally. The turbine peripheral velocity was changed by changing the PDTE operating frequency and was applied to the model to obtain the relationship with thermal efficiency. As PDTE operating frequency increased, the thermal efficiency of the model gradually approached the maximum value at a constant peripheral velocity during one PDE cycle as described above. Similar trends were observed in both tests and model predictions of thermal efficiency as a function of PDTE operating frequency i.e. turbine peripheral velocity.
The objective of this paper is applying the Time Delay Control scheme for the aircraft auto-landing guidance problem. A stability and control augmentation system and longitudinal auto-landing guidance law, using Time Delay Control, is proposed and evaluated through a simulation with model uncertainties and wind disturbances. The proposed Time Delay Control guidance law shows good performance and is robust to model uncertainties and disturbances.
The unsteady lifting surface theory for a model composed of five bladerows is developed to predict unsteady aerodynamic forces on oscillating blades of aerodynamically coupled multistage annular bladerows. The theory is formulated to calculate generalized aerodynamic forces which appear in Lagrange’s equations of blade motions, so that it can be used as the aerodynamic tool for the inter-row coupling flutter analysis of multistage bladerows. Numerical studies were also conducted to investigate the mutual aerodynamic influences among bladerows. The simultaneous effects of co-rotating upstream and downstream bladerows located at next to the next position significantly modify the aerodynamic response of oscillating blades. The aerodynamic force induced by the oscillating bladerow is not very small even on the bladerows remoter than the next-to-the-next bladerow.
A Bell-Hiller stabilizer bar is mounted on a model-scale unmanned helicopter. We investigated the rotor effect on the flapping motion of the stabilizer bar on one commercial radio-controlled helicopter as an example. Clearly the flapping motion of the stabilizer bar was strongly affected by the rotor. Model identification is definitely required when a mathematical model ignoring the rotor effect on the stabilizer bar is used.
The effect of a hole on aerodynamic forces acting on a rectangular plate in Stokes flow is shown. The effect does not depend strongly on the area or location of the hole, because the hydrodynamic forces near the hole are increased and because the effect of the hole on the hydrodynamic forces acting on the plate is decreased. This result can be used to decrease the mass of a cantilever in a micro-flow sensor without affecting its characteristics. When this micro-flow sensor is attached to a flapping wing, the decrease in sensor mass is important because inertia acting on the sensor causes deformation of the flapping wing. This result is important in understanding the flight of insects with bristled wings.