Papers by Keyword: Unsteady Flow

Abstract: The time-dependent hydromagnetic boundary layer flow across a vertical surface with internal heat regeneration in porous media is investigated. The flow problem has been modelled mathematically in partial differential equations along with appropriate defined boundary conditions. These equations were expressed in dimensionless form using suitable similarity variables. The resulting dimensionless equations along with the conditions defined at the boundaries are solved by means of the Laplace transform methods. Results of the study are graphically illustrated for various quantities of practical importance. It was concluded that time positively influence the flow as a reduced skin friction coefficient was observed. Furthermore, the magnetic parameter, the radiation parameter, the heat absorption parameter and the permeability of the porous media can be used to influence the characteristics of a flow in porous media.

Abstract: An unsteady magnetohydrodynamic natural convection transfer of mass and heat flow over a vertical porous sheet under the influence of thermal radiation and thermo-diffusion effect. The dimensionless governing equations are solved analytically by employing Laplace transform technique. The impact of various physical parameters on momentum, energy and concentration are discussed and analyzed with the aid of graphs. Furthermore, the numerical values for local Skin friction, Nusselt number and Sherwood number are noted and examined. Increasing the values of thermal diffusion results in increasing of the concentration, but it decreases with Schmidt number. Skin friction reduces for increasing values of thermo-diffusion are discussed with the help of tables.

Abstract: The present investigation has put a focus on the hydromagnetic boundary layer unsteady flow of a nanofluid over a stretching sheet. A new heat flux model named Cattaneo-Christov is applied as the substitution of classical Fourier’s law. Buongiorno’s model is incorporated. The coupled non-linear transformed equations are solved numerically by using shooting technique with MATLAB bvp4c package. The obtained results are presented and discussed through graphs and tables in detail. Our results reveal that the unsteady parameter reduces all the three boundary layer thickness. The thermal relaxation parameter exhibits a non-conducting nature that makes the decline in fluid temperature.

Abstract: A theoretical and numerical examination has been completed to talk about the unsteady, two dimensional slip flow of a nanofluid of heat and mass transfer with transverse magnetic field was investigated in this paper. A stretching surface is used to investigate the flow. Obtained nonlinear equations are solved by Spectral Relaxation Method (SRM) technique and the results are verified by comparing the results obtained by using the Matlab in-built boundary value problem solver bvp4c, and the outcomes which are published in previous papers. The outcomes are exhibited pictorially and talked about difference coming about parameters. Expanding heat transfer rate, mass transfer rate and velocity slip raises velocity yet to be diminishes temperature and skin friction (surface shear stress).

Abstract: Spring analogy method for dynamic unstructured grids is studied. The stiffness of the springs in the vertex spring method is analyzed. Improvements considering squashing spring effect and boundary effect are developed to the standard method. Applications of the improved spring analogy method to dynamic grids generation show that the new method greatly improves the deforming ability and the quality of the grids. This improved unstructured dynamic mesh method, coupled with ALE Euler solver, is then applied to simulate unsteady transonic flow about harmonious oscillation of rigid wing and bend-torsion oscillation of high-aspect ratio sweepback wing of High-Altitude-Long-Endurance Unmanned Aerial Vehicles; computational results are in good agreement with those of other literatures and experiments

Abstract: A one-dimensional numerical model was developed for unsteady-flow in a large-scale conveyance channel with complex inner boundary conditions. Using Taylor expansion and finite difference method, this model incorporated three types of inner boundary conditions, including regulators, inverted siphons, and flumes with parallel connections. It can facilitate continuous simulation with large-amplitude variations in water level and flow discharge during the flow transitions. Transition flows were simulated by this model, which were caused by the operation of a single gate of the Middle Route of the South-to-North Water Diversion Project. The discharges of simulation were consistent with the discharges of formulas calculation, and the water level variations accords with hydraulic law. The results indicate its efficiency and applicability on simulating hydraulic response of large-scale conveyance channels with complex inner boundary conditions.

Abstract: Based on the analysis of the flight stability, the research progress of the unsteady aerodynamic model was comprehensively introduced. Bryan, first of all, the aerodynamic load of traditional dynamic derivative model is put forward, still used today in some engineering issues. However, Bryan state parameters of the model is not complete, not exactly reflect the unsteady aerodynamic force time history effect and nonlinear effect. Etkin models, by retaining the item of high order Taylor expansion, including the influence of nonlinear effect. Improved Etkin model can explain the actual flight of some of the common transient response, including due to stall the mutation and aerodynamic force/torque caused by unsteady flow dynamic bifurcation and chaos of the aerodynamic force/torque value and uncertain phenomenon. Finally, the unsteady flow field of a reduced order model development trends and application prospect were analyzed, and pointing out that the CFD simulation is still accurately predict the plane stability and handling the most important method.

Abstract: Dynamic stability parameters (dynamic derivatives) are important indicators for the control system design, orbit design and longitudinal and horizontal dynamic stability analysis of aircrafts. Methods that evaluate the quality and dynamics of an aircraft typically include flight experiment, wind tunnel testing and theoretical calculation, with one of the most important part of them being the obtainment of dynamic derivatives. Project estimation method derivative action is not considered suitable for boundary layer transition, flow separation and re-attached and the complex situation leeward area vortex small angle of attack linear range. Frequency domain is a dynamic non-scheduled periodic invariant system to get moving derivative calculation method, but the accuracy of the unsteady flow is much lower than the time-domain calculations. Currently, unsteady CFD approach represents a time-domain nonlinear aerodynamic characteristics predicted the most advanced level. Derivative prediction efficiency and adaptability under conditions of high angle of attack of the development trend of nonlinear dynamic derivatives were analyzed. As a global trend, obtaining dynamic parameters through numerical calculation is becoming a prevailing approach to dynamic parameter research.

Abstract: The series hydraulic softwares of HEC-RAS is a set of softwares volumes with strong functions and broad uses in overseas. They play an important part in river hydraulic analysis、hydrology simulation、flood forcasting、river renovation and reservoir managition and programmings.The paper introduces the composition and the function of HEC-RAS model, a one-dimensional steady and unsteady flow models were established.Using this model, the designing water surface is analogized, its operation pattern is discussed, water surface profile of some water supply works are simulated.The result indicates that the application of HEC-RAS is simple and convenient,its applicability is good.

Abstract: Used the numerical method, considered the rising speed of head of seepage deformation, with the aid of the method of particle flow in micro layer to study the occurrence and development of the law of seepage failure. Numerical simulation was designed based on the study of the theory. Conducting piping tests of the soil samples by controlling water head. The results show that, the effects of loaded once on the orifice area was large, and also the most insecure. And the test result verifies the correctness of theoretical analysis. The results are valuable to further probing into the piping mechanism in sandy soils.