AEROSPACE KNOWLEDGE AND TECHNOLOGY JOURNAL
Year:2018 | Volume:6 | Issue:2 |Papers Count:10

Two-phase and multi-phase flows are the common flow types in fluid mechanics engineering. Among the basic and applied problems of these flow types, stratified flow is the one that two immiscible fluids flow in vicinity of each other. In this type of flow, fluid properties (e.g. density, viscosity, and temperature) can be different at two sides of the interface of two fluids. The most challenging part of the numerical simulation of stratified flow is to determine the location of interface, accurately. In present work, an interface tracking algorithm is developed based on Arbitrary Lagrangian-Eulerian (ALE) approach using a cell-centered, pressure-based coupled solver. To validate this algorithm, analytical solution for stratified flow in presence of gravity is derived and then, the results of the numerical simulation of this flow are compared with analytical solution at various flow conditions. The results of the simulations show good accuracy of the algorithm despite using a nearly coarse and uniform grid. Temporal variations of interface profile toward the steady-state solution show that the more difference between fluids properties (especially dynamic viscosity), will results in larger traveling waves. Gravity effect studies also show that positive gravity will results in reduction of and negative gravity leads to increasing the thickness of the heavier fluid with respect to the zero gravity condition. However, the magnitude of variation in positive gravity is much more than negative gravity.

The main goal of the present paper is development of the unsteady turbulence modeling using the URANS algorithm and preservation of numerical performance and assessment of this method respect to the RANS model in numerical simulation of a sonic jet in supersonic cross flow. The turbulence modeling used in both algorithms is the Spalart Almaras model. To improve accuracy of the computations, the structured multi block grid is used and to decrease the computational cost, the OMP parallel processing is applied. In this paper, firstly, the governing equations of both the RANS and URANS are described and then the developed code is used to analyze a 3D jet in cross flow. The results including flow structure, distribution of the pressure and velocity profile are compared with experimental data. The URANS method show more accurate results than the RANS model in numerical simulation of the sonic jet in supersonic cross flow.

This paper aims to study the effect of nanofluid on the thermal performance of a heat pipe with three evaporators for satellite equipment cooling. Nanoparicls of Cuo and TiO2 were considerd for modeling. The mathematical expressions of temperature distribution of heat pipe wall, which are analytically derived by separation of variables technique, consist of infinite series that were solved by Matlab software. The accuracy of simulated results was validated against available experimental data and a good agreement was observed between them. The results show that the use of nanofluid instead of water leads to a more temperature reduction of satellite equipment as well as a more temperature uniformity throughout the wall of heat pipe. Moreover, increasing of nanoparticle concentration and reducing nanoparticle diameter have a remarkable effect on the heat transfer enhancement, thermal resistance reduction, and thus thermal performance of heat pipe. Under the best condition, growing CuO nanoparticle with diameter of 10nm up to 8% increases heat transfer coefficient up to 75%. The use of nanofluid reduced the required heat transfer surface and the weight of heat pipe in best cause (8% CuO nanoparticle with diameter 10nm) decreases down to 35%. The outcomes of this paper indicate that metal oxides nanofluids can have a great potential in satellite equipment cooling.

The purpose of this paper is investigation of the influence of turbulent flame formation by using laminar Flamelet model on combustion characteristics in a gas turbine model combustor. The effect of number of laminar Flamelets and their scalar dissipation rate on reactive flow characteristics such as temperature, scalar dissipation rate of flame, concentration of species and NO emission are the results of this paper. In order to solve the governing equations of non-premixed combustion of Kerosene liquid fuel in a gas turbine model combustor, the Finite Volume method is employed. The Realizable k-ε turbulence model, steady Flamelet combustion model and chemical mechanism with 26 reduced reaction and 17 species are applied to simulate two-phase reacting flow in this combustor. This study is performed in three different Flamelet cases and their results are compared with available experimental data. The results show that the effect of laminar Flamelet numbers and the maximum scalar dissipation rate of flame on the velocity of flow is negligible. However, the flame temperature is affected from these parameters. In the case that the flame consists of greater laminar Flamelets numbers and the maximum scalar dissipation rate, less difference between simulation and experimental temperature is observed. By reducing the laminar Flamelets numbers and the maximum scalar dissipation rate, the stretch of flame is reduced, higher temperature and higher NO emission are predicted.

This study aims to design and construct a hot-gas Thruster or pintle valve for this purpose at first, utilized the characteristics and inverse design methods which made no desirable results because of their limitations. Thus the method of prediction and correction in Computational Fluid Dynamics (CFD) was implemented. Then the sensitivity analysis of those paramethers impacting on the Thruster performance such as the diameter’s throat and etc, examined and at last a suitable design with reliability coefficient of 1.20 for a thruster with 32000 N thrust was done. Then the angle of entering hot-gas was surveyed, which showed 30 degrees as the optimum value. Then the designed valve in the worst status (from Thrust point of view) with the angle of 90 degrees of entrance to be tested in vitro. The experimental results of the Thrust show a good conformity to the simulation model results with less than 10% of errors.

Attitude dynamics simulators are one of the most common facilities utilized in spacecraft attitude and stability researches, because these systems produce a free and unconstrained rotational motion. Therefore, they (spacecraft attitude dynamics simulators) provide a platform to perform practical tests on satellite or spacecraft in easy way. Simulation of space environment (such as frictionless, torque free and unconstrained motion) is the best specification of such devices that help scientists (or specialists, students and space users) to have constrained or unconstrained platforms for three (3) degrees of freedom motions. This paper (article) intends to present a novel classification of satellite (spacecraft) simulators in first phase (level) and then tries to focus on air-bearing-based simulators and presents a survey of them (spacecraft attitude dynamics simulators). Investigation of available sample of satellite simulators and verification of them are the other specifications of this article caused to be a good reference for students and researchers.

Measurement data of guidance sensors are commonly lost and delayed in ground to air missile systems. These phenomena affect the missile efficiency. Kalman filter is used to estimate the variables needed in implementation of guidance law. But the performance of Kalman filters is dependent on the knowing exact model of the system. In practical problems, the exact parameters of the systems model, especially the one of delay and loss is not known. In this study, adaptive Kalman filter is employed to compensate the uncertainty in the stochastic model of delay and loss which is employed in a line of sight guidance algorithm of a defensive missile. A set of recursive difference equations are used to obtain the adaptive filter gains. The problem is formulated in presence of delayed and missing measurements, then the adaptive filter structure and correction factor are presented. Simulation results are presented to verify the improved performance of the approach.

Flight simulators as an integral component of today aviation industry, play an important role in training the pilots and development of the new equipment. Optimal motion cueing beside the positive characteristics of easy computation and implementation, due to limited performance in keeping the motion system within the workspace in complex maneuvers, is faced with serious obstacles. Predictive control method featured with inherent capabilities of dealing with constraints on inputs and state variables, while maintaining the high quality of the output, is faced with progressive development. The task of model predictive control is solving the optimal problem over the control horizon to accommodate the feasible movement of the flight simulator by decreasing as could as the difference of the perception of motion between the pilots in real vehicle and the simulator. This approach is based on minimizing the quadratic cost function incorporating the sensation of motion, the motion system configuration related state variables as well as input control signal. Although in this method, the design of washout filters are not needed. In this article, the systematic design of motion cueing algorithm based on model predictive control is described and its performance in comparison with optimal washout filter cueing method is illustrated. The proposed motion cueing method posing with much limited and smoother movements in surge-pitch maneuver tends to efficiently maintaining the motion system with in its workspace while preserving the same sense of motion. This results in increasing the capabilities of the motion system to be employed in much complex maneuvers.

Persistent surveillance is one of an important problem in the field of aerial investigation, border patrolling, surveillance and search, Which distinguishes it from other matters by revisit time of major area. The main point of our problem is the minimizing of the time interval between two consecutive hits for a particular area that makes the details and dynamics tracking with higher accuracy. In this paper in order to achieve the minimum revisit time, the heuristic function based on the waypoints time age was used. This function defines the value of each point with the weight functions that optimized by genetic algorithm in several successive iterations. These optimal values are dependent on the position of major point and number of UAV. In multi-agent problems, the patrolling pattern is determined by heuristic weight function in several iterations. Some basic patterns such as lawn mover and spiral are organized to calculate the minimum traveling distance in the search area and obtain the comparative criteria for the results. The paper results lead to improved the navigation during aerial patrolling the area with the graded region, with respect to the UAV dynamics and minimum revisit time.

In this study, the effect of lattice geometry on the modal response of cylindrical carbon/epoxy lattice structures have been investigated both experimentally and numerically. Two structural geometries of triangular and hexagonal were chosen. Accurate flexible molds were used to manufacture the carbon/epoxy composite samples using polar-winding process. Experimental and numerical investigation of the vibration response of the manufactured samples were analyzed in order to determine the natural frequency and modal response for both triangular and hexagonal lattice structures for simply supported beam conditions. The results obtained from the Numerical model shows a good agreement with experimental results. after validating the numerical model, other supporting conditions like simply -fixed and fully fixed support was investigated Numerically. Results shows that the triangular structure lattice has higher natural frequency than hexagonal structure for all different support conditions.