Numerical investigations are conducted to study the tip leakage flow and cooling effectiveness on various film-cooled squealer tips. The effect of partial squealer rims on the leakage flow structure, tip leakage loss and tip film-cooling effectiveness is illustrated under four blowing ratios by considering the relative motion between the turbine blade and the stationary casing. Six cutback configurations of partial squealer rims, including three pressure-side trailing-edge cutbacks and three suction-side trailing-edge cutbacks with different cutback lengths, are considered in total. Two types of film-hole arrangements are used, both having the same film holes. In the first type, 13 film holes are arranged uniformly along the middle camber line (referred to as CL mode). In the second type, seven film holes are located in the vicinity of the leading-edge and the remainder of the film holes are arranged near the suction side in the mid-chord region (referred to as LE mode). It is found that the partial squealer with cutback near the trailing-edge produces larger tip leakage mass flow ratios than the full squealer, especially for the suction-side squealer cutback. However, the blade tips with a suction-side squealer cutback are conducive to reducing the tip leakage loss, especially for the partial squealer with a moderate cutback length. Furthermore, the suction-side squealer cutbacks can improve the tip film-cooling effectiveness at the trailing-edge of the blade to a great extent. It is also confirmed that the LE mode produces a more uniform and higher tip film-cooling effectiveness than the CL mode.
This paper presents a method to obtain a robust optimal path in an environment with time-varying safety features, such as in the lunar polar region. In designing the path for planetary exploration rovers, we must consider various safety conditions, such as terrain hazards, illumination, and communication visibility to the Earth. Some of the safety features are time-varying, and the optimal path should be searched for both the spatial direction and the temporal direction. In addition, there is no guarantee that all of the sequences will be successfully executed on time due to misoperation, failures, or trouble. Therefore, a path that is robust against the delay must be planned so as to guarantee safety even when behind schedule. The authors propose an algorithm called “Robust Spatio-Temporal Path Planner for the Planetary Rover (Robust-STP3R)” to obtain a path that is robust against schedule delay in a time-varying environment. This method defines a cost function that consists of the distance as well as the region type cost. To add robustness against schedule delays, the authors consider a weighted summation of the time-varying region type cost with regard to the temporal direction. The effectiveness of the proposed method is demonstrated through use in a simulated lunar polar exploration exercise.
The aeroacoustic fields of twin jets and the equivalent single jet were experimentally investigated using particle image velocimetry (PIV), schlieren visualization, and acoustic measurement. The present study focuses on the aeroacoustic fields of the twin jets, and the effect of the interaction between each jet was investigated using various nozzle spacing. The PIV results indicated that strong interaction causes elliptical jet growth on a cross-stream plane and a decrease in the Reynolds stress of the inner shear layer on a plane containing both jet axes. The dynamic mode decomposition of the double-pulsed schlieren images extracted the interaction of each jet, which relates to the Mach wave generation. The noise of the twin jets was basically quieter than the noise of an equivalent single jet because of a shielding effect and a reduction in the Reynolds stress resulting in a decrease in the overall sound pressure level.
Research on supersonic transport seeks to overcome two main challenges, to mitigate sonic boom and improve aerodynamic performance, in order to become environmentally viable and economically practicable. To achieve these goals, this research proposes a waverider configuration to solve the challenge of designing commercial supersonic aircraft. The waverider is famous for providing a higher lift-to-drag ratio than that provided by other conventional designs for supersonic and hypersonic flights. The study of three types of supersonic waveriders, cone-derived, power-law, and osculating-cone waverider, is introduced for low-supersonic designs. The flight condition includes a speed of Mach 1.5 at an altitude of 18,000 m. An unstructured grid with an inviscid Euler equation solver is used to calculate the flow field of the vehicle. The ground noise post-processing uses an augmented Burgers equation solver to assist in far-field signature evaluation. The result of a cone-derived waverider provided significant volume with low overpressure, while the power-law waverider showed the advantages of aerodynamic performance and ample design space. The osculating-cone waverider obtained the merits from both the cone-derived and power-law waveriders. The waverider is expected to have a quality that satisfies the design objectives of supersonic aircraft: high aerodynamic performance and sonic boom mitigation.
A whirling arm is an effective device to measure propeller characteristics at low advance ratios. In the authors’ preceding research, an apparent advance ratio was adopted to determine propeller characteristics. The apparent advance ratio is determined only by the relative airspeed of the rotating arm and propeller in still air, and is used in wind tunnel measurements. However, in the case of whirling arm measurements, the advance ratio should be determined appropriately considering the additional airspeed induced by propeller wakes and swirling flow generated by the rotating arm. To address the above issue, we propose an airspeed model of blades considering velocity fields induced by the surrounding vortices. We also propose a procedure to calculate an appropriate advance ratio and the steady characteristics based on the proposed model. The validity of the proposed airspeed model is evaluated by making a comparison with the results of wind tunnel experiments. The corrected propeller characteristics using our airspeed model shows good consistency with the data referred from an existing propeller characteristics database.
Recently, the application of a deep-learning technique to fluid analysis has been suggested. Additionally, a deep-learning-based method called the Deep Galerkin Method (DGM) has been suggested for solving a partial differential equation. In DGM, a loss function for training a deep neural network is formulated so that differential operators, boundary conditions, and initial conditions of the targeted partial differential equation are satisfied. This study aims to extend and apply DGM to solving compressible Navier-Stokes equations and examine the feasibility of using DGM for fluid analysis. In this paper, DGM is applied to two-dimensional Burgers equations with periodic boundary conditions, one-dimensional Navier-Stokes equations for a shock tube problem, and two-dimensional Navier-Stokes equations for the supersonic flow around a blunt body. The approximate solutions obtained using DGM show generally good agreement with that obtained using a finite difference method.