Journal of Aerospace Science and Technology
Volume:15 Issue: 1, Winter and Spring 2022

The main purpose of this article is to examine the periodic coupled orbit-attitude of a satellite at restricted three body problem considering both primaries oblateness perturbations. The proposed model was based on a simplified coupled model meaning that the time evolution of the orbital state variables was not a function of the attitude state variables. Since, the problem has no closed-formed solution, and the numerical methods must be used, so the problem can have different periodic or non-periodic responses to the initial conditions. The initial guess vector of the coupled model’s states was introduced to achieve the optimal initial conditions leading to the periodic responses, and then the P-CR3BP coupled orbit-attitude correction algorithm was proposed to correct this initial guess. Since, the number of periodic solutions is restricted; the suitable initial guess vector as the inputs of the coupled orbit-attitude correction algorithm increases the chances of achieving more accurate initial conditions. The initial guess of orbital states close to the initial conditions of the P-CR3BP periodic orbit, along with initial guess vector of attitude dynamics states with Poincaré mapping was suggested as the suitable initial guess vector of the coupled model.

Regardless of the initiation or propagation procedure of crack in a gas turbine blade, the precise expectation of the fracture behavior, such as mixed-mode Stress Intensity Factors (SIF), plays a significant role in acquiring its operational life. Therefore, multilateral three-dimensional fracture solutions are required, including real-based mixed-mode loading (I/II/III) conditions and geometrical considerations. In this study, three-dimensional semi-elliptical crack in a gas turbine blade with various geometrical parameters and inclination angles under mixed-mode loading (I/II/III) conditions were investigated based on the employing finite element techniques and analytical procedure. In this context, the semi-elliptical crack has been considered in the critical zone of the rotating blade to achieve the effect of crack aspect ratio, rotational velocity, crack location, and mechanical properties. Fluid Solid Interaction (FSI) analysis was also performed in addition to solid functional enriched elements. Structural simulation is done at the speed of 83.776 m/s based on CFD simulation. The results indicated that Al Alloys blade shows a profitable resistance in crack propagation. Moreover, as the crack domain is near the location of x/c= 0.25 and 1.9 of crack front, the mode II SIF will be independent of rotational velocity and the blades' mechanical properties. Similarly, for the location of x/c= 1.1 in crack front, the mode III SIF is independent of rotational velocity and blades' mechanical properties.

In this study, terminal phase guidance of a vertical-landing booster has been considered. At first, dynamical equations have been derived assuming variable mass, density and gravity model. Then by considering these parameters as constants, sensitivity variables have been extracted using the vectorized high order expansions method. By using these sensitivity variables, a guidance law for updating optimal path and commands has been given. By implementing this guidance law, and considering initial deviations, near optimal path and guidance command have been extracted online, and the performance has been studied by means of simulations. To this end, intrinsic errors of the theory has been considered and confirmed at first. Then, a set of simulations considering variable mass, density and gravity have been implemented and the performance of the method has been evaluated in the presence of a vast variety of initial deviations. By investigating the results, which have been presented as graphs and numerical errors it can be seen that the landing errors are small and for booster landing mission, the vectorized high order method shows remarkable performance.

In this article, the idea of building a supersonic wind tunnel has been provided that uses a high-pressure steam flow of a combined cycle power plant. This has been investigated by CFD method. Using the plant's output steam as a high-pressure source can be used in the ejector to create supersonic airflow in the test chamber. For this purpose, first, the numerical model has been validated in comparison with the previous numerical and experimental results. The numerical model used is the viscous compressible flow, which is performed by the k-ω-SST turbulent modeling of the turbulence model. All calculations are performed in ANSYS-FLUENT software. After validating the numerical process, various geometries have been proposed to achieve the ultrasonic secondary flow and each structure is examined numerically separately in a range of functional conditions. Through trial and error method and looking at the achievements of previous research, in a very long process and by testing several different structures, a suitable structure has been obtained to achieve the supersonic testing chamber. This structure has been studied parametrically under different functional conditions. It has been shown that the proposed structure can generate an ultrasonic flow in an acceptable range of power plant steam flow and pressure. This structure has been proposed for the first time in the literature in this field, and in no previous research has such a structure been proposed. Access to the ultrasonic secondary flow is also a major innovation of this research.

In this paper, a multi-input/multi-output sliding controller is proposed and analyzed for a quad tilt-wing unmanned aerial vehicle (QTW-UAV). The vehicle is equipped to do take-off and landing in vertical flight mode and is capable of flight over long distances in horizontal flight mode. The full dynamic model of the vehicle is originated from the Newton-Euler formulation. For developing the controller, a set of integral type sliding surfaces is selected and it is necessary to mention that in this approach, there isn't any linearization during controller design. Simulation has been conducted for a nonlinear, multivariable model that includes uncertain parameters and in the presence of pitch angle measurement noise and pitch moment disturbance. For verification, the proposed controller is compared with linear based controller design simulation. Results exhibit that the proposed controller is robust in the face of uncertainties, noise and disturbance and meets performance demands with control inputs of low amplitude.

The calculation of aerodynamic heating is one of the most important steps in designing high speed flying bodies, especially reentry bodies. Because ignoring that, it can damage the thermal protection system and cut off the radar connections to the reentry capsule. Due to the high speed of the capsule and the lack of a material medium, the radiation heat transfer rate is important in comparison to the convection heat transfer rate of the displacement in determining the total thermal flux, and ignoring it in the calculations caused many errors in the determination of the total heat flux . In this paper, various parameters affecting the heat transfer rate of the nose of the reentry capsule have been investigated. To calculate the capsule nose radiation, a theoretical method is presented which is compared with the reference simulation results to confirm its correctness. In this simulation, the heat transfer rate of the Apollo4  capsule has been investigated. Due to the low optical thickness of the model, the DO radiation model is used to simulate CFD. This simulation was carried out using Fluent software version 16 and solved with a laminar flow of gray gas and non-gray gas. The results show that the radiation heat transfer rate in non-gray gas mode is lower error than the gray gas state, and it is also observed that at high altitudes, the radiation transfer rate is 80% of the total heat transfer rate.

The use of Unmanned Aerial Vehicles (UAVs) with different features and for a variety of applications has grown significantly. Tracking generic targets, especially human, using the UAV's camera is one of the most active and demanding fields in this area. In this paper we implement two vision-based tracking algorithms to track a human by using a 2D gimbal which can be mounted on UAVs. To ensure smooth movements and reduce the effect of common jumps on the trackers output, the gimbal motion control system is equipped with a Kalman filter followed by a proportional-derivative (PD) controller. Various experimental tests have been designed and implemented to track a human. The evaluation results show success in tracking the high speed movements with one of the algorithms and high accuracy in tracking the challenging movements in the other algorithm. Also in both methods, the tracking computation time is short enough and suitable for real-time implementation. The favorable performance of both algorithms indicate the ability of designed system to be implemented on the UAVs for practical applications.

In this study, the static and dynamic analyses of a modified integral pulse-width pulse-frequency (PWPF) modulator with small error-reset integrator (SE-RI) logical circuit are carried out using grid search method. A set of quasi-normalized equations is utilized in order to reduce the number of parameters, that is, the integrator gain and the maximum torque of modulator are merged to other parameters. The output of the modified integral PWPF (IPWPF) modulator is limited to 50 Hertz.The preferred regions of the IPWPF are chosen by the amount of limitation on fuel consumption and thruster firings. These preferred regions are obtained for different dead zone values of SE-RI circuit. The analyses are performed in two methods with different choices of Schmitt-trigger parameters (i.e., hysteresis or threshold ratio). The proposed regions described by simple inequality relations represent the rectangular regions, which does not give the whole preferred region. As an advantage of the study, the preferred regions are presented graphically instead of rectangular regions by inequality relations.

In this paper, flow and heat transfer inside a helicopter shell and tube heat exchanger is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are produced longitudinally and integrally with the tube body. The current flowing in the shell is MIL-PRF 23699 oil and the flowing fluid in the tubes is JP-4 fuel. These two fluids flow in opposite directions and exchange heat with each other. Using Aspen software, the design is done in such a way that the heat exchanger has minimum length and weight to have a better and higher effect on the efficiency of the helicopter. To investigate the effect of tube geometry and oil mass flow on the heat transfer between fuel and oil, simulation has been performed in ANSYS Fluent program. In this simulation, a part of the whole heat exchanger is selected as the geometry and the effect of changing the geometry of the tubes, mass flow of fuel and oil on the heat transfer coefficient, Colburn coefficient, coefficient of friction and their ratio, and outlet temperature changes are investigated. The results of this simulation show that the heat transfer rate between fuel and oil for a heat exchanger with finned tubes is about 11% higher than without a fin. Also, reducing the mass flow of oil entering the shell increases the efficiency of the heat exchanger.

Flight simulation is a powerful and usefull instrument in design, testing, evaluation and validation of aircrafts; The results of aerolastic simulation along with rigid simulation can be used in the many areas of designs, such as modification or optimization, stability analysis and evaluating field test data; It can be said that the use of simulation in the fields of design and optimization, especially during the initial and detailed design, should be considered more than other fields; In this research, by use of simulation, the effect of some design parameters such as slenderless ratio, maneuvering acceleration, propulsion curve, natural frequency of the structure, aerodynamic load distribution , etc. On issues such as flight and tracking behavior, stability and collision accuracy, has been examined; In cases such as: evaluating the initial error or veviation of the thurst vector or its curve, rolling speed, tracking of control commands, etc. aerolastic simulation gives a more realistic output compared to rigid simulation; Further more in cases such as investigating the effect of aerodynamic load distribution or stiffness ans and mass distribution, only aerolastic simulation is able to respond. Accordingly, the main orientation of this research is to develop an approach with acceptable accuracy and speed in order to simulate elastic projectiles in order to achieve some of the mentioned goals; However, due to the wide range of effective parameters and their interaction, in this study, only the role of thrust and body rigidity has been examined.

Aero-engine entrance conditions are not always ideal and, for various reasons, inlet distortion may occur and cause inlet blockage and reduction of compressor performance. The aim of this study was to numerically simulate the effects of plasma actuators on the enhancement of low-speed axial compressor rotor performance under radial inlet distortion. First, compressor performance under radial inlet distortion with 15% and 20% blockage and theirs destructive effects on stall margin was investigated. Then, the effect of plasma actuators on rotor loss subjected to inlet distortion was investigated, using an algebraic model based on the plasma actuators physics in form of body force distribution in Naiver-Stokes equations. The results show that radial inlet distortion causes decreasing stall margin of the compressor. In addition, according to the findings, applying plasma actuators boosts the flow momentum behind the distortion screen and reduces the blockage of the rotor tip region, leading to decreasing losses. Furthermore, at 15% blockage, the plasma actuators caused to increase the stall margin from -11% to -5% versus the rotor in clean condition.

This study presents the miss distance analysis of the first-order explicit guidance law due to seeker noise using the adjoint method. For this purpose, linearized equations are utillized and the adjoint model is developed. Then the first-order equations are obtained and converted into nondimensional ones. The analysis is carried out for different values of the power of the alpha function, defined as the time decrease rate of the zero-effort miss distance to unit control input. The unity power gives the first-order optimal guidance strategy, minimizing the integral of the square of the commanded acceleration during the total flight time.The seeker and control system is assumed as a fifth-order binomial transfer function. Due to computational error and stability consideration, the effective navigation ratio is kept constant for very small time-to-go until intercept, which its effect on the miss distance is also investigated. Finally, approximate formulas are obtained using curve fitting method for rms miss distance due to seeker noise.