A new turbine blade tip shape called triple squealer is proposed. This shape is based on the conventional double squealer, and the cavity on the tip surface is divided into two parts by using a third squealer along the blade camber line. The effect of the ratio of groove depth to span (GDS ratio) was investigated. The flat-tip case (baseline case) and double-squealer case were calculated for comparison. In-house, unstructured, 3D, Navier-Stokes, finite volume, multiblock code with DES (Detached Eddy Simulation) as turbulence model was used to calculate the flow field around the tip. The computational results show that the reduction in the mass flow rate of the leakage flow for the triple squealer is 15.69% compared to the flat-tip case.
This paper addresses a novel vector-based attitude determination algorithm on the basis of geometrical configuration of external reference vectors. The proposed method called a geometrical attitude determination algorithm can be used for the attitude estimation of moving vehicles when two external reference vectors are partially measured on three orthogonal body axes. Applications of the new method range from the ground robotics navigation to satellite attitude control. Numerical simulations demonstrate that the algorithm can be reliably utilized for the three-axis attitude determination in the presence of inaccurately-measured reference vectors.
Acoustic noise from the trailing edge of 2D airfoils is known to be discrete at certain moderate Reynolds numbers. The most widely accepted explanation for this phenomenon is the acoustic linkage between acoustic radiation and Tollmien-Schlichting (T-S) disturbances growing in the airfoil boundary layer. This paper has two objectives: (1) is to devise a technical method for suppressing or abating trailing-edge noise from a practical viewpoint; (2) is to obtain evidence whether or not T-S instabilities are associated with the frequency selection mechanism mentioned in the literature. From previous experiments (Atobe, T., et al., Trans. Jpn. Soc. Aeronaut. Space Sci., Vol. 52, pp. 74–80, 2009), generation of trailing-edge noise is dominated primarily by suddenly amplified unsteady disturbances in the presence of reverse flow on the pressure side of the airfoil rather than the suction side. Therefore, the boundary layer near the trailing edge on the pressure side is disturbed artificially with distributed roughness elements. As a result, the separation is swept away, and the trailing-edge noise is drastically suppressed. We reconfirmed that under the natural configuration with sound emission, most unsteady disturbances are not amplified by T-S instabilities, but rather by other inflectional-type instabilities. The frequency selection mechanism in the tonal noise generation process remains unsolved.
Uni-element combustion tests were conducted employing double swirl coaxial injectors fed by liquid oxygen and kerosene. In this study, two major experimental parameters have been considered: the recess length and fuel swirl chamber shape. It was revealed that combustion efficiency depends mainly on the mixing mechanism for the present swirl coaxial injectors, and acoustic intensities become reduced with a decrease of the recess length. Low-frequency pressure oscillations around 200 Hz have been observed for all injectors. Dynamic behavior examined by the measurements of pressure fluctuations considerably differs for external and internal mixing based on the recess length. Internal mixing induces a mixture ratio and a total mass flow rate that vary with strong bias at a single frequency, resulting in high-amplitude pressure fluctuations generated by combustion of pulsating coherent flow structures. However, the results for external mixing show that the fuel and oxidizer mixture flow carries more dispersed, multiple-wave characteristics due to the broad mixing region as well as disintegration and merging phenomena of propellant sheets before mixing.
The optimal guidance law of an autonomous four-rotor helicopter, called the Quadrotor, using linear quadratic regulators (LQR) is presented in this paper. The dynamic equations of the Quadrotor are considered nonlinear so to find an LQR controller, it is necessary that these equations be linearized in different operation points. Due to importance of energy consumption in Quadrotors, minimum energy is selected as the optimal criteria.
The fiber-optic gyroscope is used widely utilized as an important component of spacecraft inertial navigation system. Although it has several good characteristics over conventional gyroscope techniques, there is still some drift. To obtain high performance and diagnose faults in fiber-optic gyroscopes, error and drift must be found. Although many approaches have been proposed to filter drift in attitude determination, the solutions are in adequate. The stellar sensor has no integration drift making it very suitable for finding drift in fiber-optic gyroscopes. We proposed a novel fiber-optic gyroscope drift extraction algorithm using the stellar sensor to generate the vehicle reference rotation rate. Simulations of the algorithm are described an verify the proposed algorithm.
Hayabusa, launched in May 2003, is the first Japanese spacecraft to have explored the small asteroid Itokawa (1998SF36) and has touched down on Itokawa twice. LIDAR (LIght Detection And Ranging) technology has been developed as an important navigation sensor with the characteristics of light weight (3.7 kg) and wide dynamic range (50 km to 50 m). The performance of LIDAR was perfect in the on-orbit operation and led to Hayabusa successfully touching down on Itokawa. This paper introduces the components of the LIDAR system and discusses ranging results of the onboard operation. For hardware, this paper focuses on the laser module that provided a lot of knowledge and the receiver that is important for evaluating the ranging data. The evaluation is takes particular note of the behavior of the receiver.
Measurements of starting load in the indraft supersonic wind tunnel of Muroran Institute of Technology were conducted for Mach 2, 3 and 4 conditions with the AGARD-B model. The high-speed photographs covering the behaviors of the wind tunnel model from the start to end of the operation were taken. Those photographs make clear that the oscillations of the model coincide with the measured starting load oscillation and starting loads were caused by two shock waves. The first shock wave is the reflection shock, generated at the nozzle throat by expansion wave reflection. The second wave is comprised asymmetric oblique shock waves (AOS) coming from upstream. AOS can generate asymmetric conical shock (ACS) around the nose cone of the model, which would have directly caused the starting loads on the wind tunnel model. Based on these observations, propose a conical shock theory, as an alternative starting load prediction theory instead of the normal shock theory.
LOX/LH2 subscale rocket nozzle flow fields are simulated computationally using the 3D compressible Navier-Stokes equations. The area ratio of the nozzle is 140 and the film coolant hydrogen gases are injected from 30 film cooling holes distributed circumferentially at an area ratio of 13. The experimental nozzle throat Reynolds number indicates that the boundary layer of the nozzle is in its transition region as the size of the nozzle is small. A clear difference in effective specific impulses of the secondary flow between the laminar and turbulent conditions is also shown. The nozzle wall temperature also influences the nozzle performance and the experimental performances were in better agreement with the laminar computations when the wall temperature is set to 300 K, which is closer to the experimental conditions. Both turbulent and laminar computations are carried out to investigate the effect of the boundary layer conditions on the nozzle performance. The computed results show that the structure of the separated flow downstream of the film cooling injection significantly changes between the turbulent and laminar conditions.