Transfer Boundary Conditions Research Articles

Validation of the “stage – diffuser” system numerical study and its use for design modernization

The efficiency of a gas turbine largely depends on the aerodynamics and pressure recovery capacity of the diffuser. For reliable numerical simulation of the flow in the diffuser, the model must be validated on the basis of experimental data on the flow structure. An experimental and numerical study of the stage diffuser system was carried out. The results of this investigation are as follows: the area of applicability of the numerical method for assessing the flow in the stage diffuser system was determined; recommendations for preparing a numerical model and transferring boundary conditions from domain to domain were developed; the importance of profiling the last turbine stage to ensure unseparated flow entry into the diffuser is indicated; the influence of the hub length and the geometry of the struts on the losses in the diffuser and its pressure recovery capacity is determined. It is shown that increasing the hub length to certain limits improves the pressure recovery ratio of the diffuser. The smallest thickness of the struts gives the best results; the tangential and axial slope of the struts does not make a significant contribution in the nominal operating mode of the gas turbine.

Research on Impact of Cooling Fan’s Geometry on Nozzle’s Heat Load of the Air-Cooled Diesel Engine

In order to study the nozzle’s temperature distribution and to reduce its heat load, the heat transfer boundary condition of nozzle has been simplified appropriately, considering the details of the convectional heat transfer inside the nozzle and the needle body contact heat transfer. Results of the simulation with ANSYS software show that the nozzle’s temperature distribution is complicated and high-temperature region are concentrated in the nozzle’s head. Considering the fact that the cooling fan plays an important role in reducing the heat load of air-cooled engine, the test points were reasonably selected to measure the needle valve body’s temperature as well as to seek reasonable cooling fan blade numbers and the blade installation angle for the air outlet in order to improve the thermal load of the nozzle. It was found that the nozzle’s temperature decreases at first but then increased when the fan blade numbers and the blade installation angle for air outlet increased, and the impact of the number of blades on the nozzle’s temperature was more significant than the blade installation angle for the air outlet. With the scheme of the blade installation angle of 132° with respect to the air outlet and with 20 blades, the temperature of the nozzle needle valve’s head and middle decreases to 21 K and 7 K on average compared with the original scheme, which has a good effect on reducing the temperature of the nozzle’s needle valve head, and the temperature gradient between two test points also reduced by 0.65 K/mm on average. It provides a reference for reducing the nozzle’s heat load.

Analytical Solution for Non-Newtonian Nanofluid with Heat Transfer and Nonlinear Partial Slip Boundary Conditions by Means of Optimal Homotopic Asymptotic Method

Analytical Solution for Non-Newtonian Nanofluid with Heat Transfer and Nonlinear Partial Slip Boundary Conditions by Means of Optimal Homotopic Asymptotic Method

Free Vibration Analysis of a Thin-Walled Beam with Shear Sensitive Material

This paper presents a method for a free vibration analysis of a thin-walled beam of doubly asymmetric cross section filled with shear sensitive material. In the study, first of all, a dynamic transfer matrix method was obtained for planar shear flexure and torsional motion. Then, uncoupled angular frequencies were obtained by using dynamic element transfer matrices and boundary conditions. Coupled frequencies were obtained by the well-known two-dimensional approaches. At the end of the study, a sample taken from the literature was solved, and the results were evaluated in order to test the convenience of the method.

Steady-state groundwater inflow into a circular tunnel

The prediction of groundwater inflow into a tunnel is important for designing the tunnel drainage system and to minimize environmental impacts and the risk of tunnel instabilities and subsidence damage. Analytical solutions exist to calculate tunnel inflow, and, increasingly, numerical groundwater models are used to this end. In order to represent different types of tunnel support structures, this study reviews different boundary conditions that can be set at the tunnel perimeter to calculate tunnel inflow and recognizes different ways to account for the tunnel lining. Analytical solutions and numerical models to calculate tunnel inflow are compared and factors influencing the accuracy of numerical solutions are highlighted. The study suggests that numerical models provide estimates of tunnel inflows with sufficient accuracy for practical purposes if the tunnel is lined and has no drainage layer surrounding the lining, and if the hydraulic conductivity of the lining is several orders of magnitude lower than the hydraulic conductivity of the aquifer, or if the lining is thick. Otherwise, the extent of the model domain must be large with respect to the extent of the tunnel to provide accurate results. It was shown that inflows are higher for lined tunnels with a drainage layer than for unlined tunnels, if the head in the drainage layer corresponds to the level of the tunnel center or invert. If the head in the drainage layer corresponds to the level of the tunnel crown, inflows are higher for unlined tunnels. The study further suggests that for unlined tunnels, inflows are higher at the invert than at the crown. For lined tunnels with a drainage layer, the reverse is true. Differences between inflows at the crown and invert decrease with increasing depth of the tunnel under the groundwater table. The numerical solution for flow into lined tunnels without drainage layer using a transfer (Cauchy type, or 3rd-kind) boundary condition produces lower inflows compared to using a specified head (Dirichlet type, or 1st-kind) boundary condition. Using a transfer boundary condition is especially inaccurate if the lining is thick.

One-dimensional analysis of thermoelement exposed to lateral heat transfer as a wall in MEMS-based thermoelectrically controlled micronozzle

Two thermoelements are formed as walls of a micronozzle to perform heating-cooling on a gas flowing between them. The model of heat transfer by conduction opposites to Peltier effect is built, including Joule heating, Seebeck effect and heat dissipation to the flowing gas. A general energy equation of one-dimensional heat flow in a TE subjected to electrical field and heat convection at the lateral side is developed and solved both analytically and numerically. The effects of varying the convection heat transfer coefficient, Joule heating and boundary conditions are tested for constant material properties using the analytical solution. Two parameters which play important roles in the thermal performance of TE are identified; heat resistance ratio and energy growing ratio. The effects of varying these two parameters as well as TE geometry have been investigated thoroughly, and the results are presented in the form of charts to assist the design and material selection of the TE.

Characteristics of thermocapillary convection in two-component fluids

The linear problem of convective instability near the surface of a stratified two-component liquid medium (for example, saline sea water) is considered. The specificity of the problem consists in need to take into account both background stratifications and a difference in the transfer coefficients and boundary conditions for two substances (heat and admixture concentration), as well as the thermocapillary effect. It is shown that there is a vast region of monotonic instability in the medium stable in accordance with all criteria previously known. The two-component nature of the medium makes the development of anomalously intense perturbations deeply penetrating into the hydrostatically stable medium possible. A dimensionless instability criterion is formulated and neutral curves are calculated.

Numerical Analysis on Thermal Field in Rheocasting-Rolling of Semi-Solid Magnesium

The process on rheocasting-rolling of semi-solid AZ91D magnesium alloy was investigated by the finite element method from the aspect of fluid mechanics .The mathematical model of the casting-rolling zone was built based on the analysis on the heat transfer mode and boundary conditions of the casting-rolling zone. The numerical simulations were carried out by different casting-rolling parameters to observe the full solidification point and find the best pouring temperature. The numerical simulation results showed that when the semi-solid slurry temperature was 584°C, magnesium strips with good structure and performance could be obtained by rheocasting-rolling. This simulation provided a valid evidence to determine the optimal process parameters.

Plane wave analysis of panel wedges

In the present work, a wedge structure made of absorbing panels has been analyzed by making use of the matrizant analysis with the help of the Boundary-Condition-Transfer (BCT) algorithm. The rectangular panel wedge, as it is called in this manuscript, is simple in geometry. The theoretical model, based on the plane wave acoustical coupling between multiple interacting ducts of variable cross sectional area, is applied to predict the pressure reflection coefficient of the present wedge configuration. Bulk reaction and hence wave propagation in the wedge material has been assumed in the proposed model. An asymptotic solution using the Peano-Baker series of matrix calculus is derived for different variable area ducts and then solved with the aid of the boundary condition transfer algorithm. A brief parametric study is also included as an aid to designers.

Effect of boundary conditions and convection on thermally induced motion of beams subjected to internal heating

Numerical exercises are presented on the thermally induced motion of internally heated beams under various heat transfer and structural boundary conditions. The dynamic displacement and dynamic thermal moment of the beam are analyzed taking into consideration that the temperature gradient is independent as well as dependent on the beam displacement. The effect of length to thickness ratio of the beam on the thermally induced vibration is also investigated. The type of boundary conditions has its influence on the magnitude of dynamic displacement and dynamic thermal moment. A sustained thermally induced motion is observed with progress of time when the temperature gradient being evaluated is dependent on the forced convection generated due to beam motion. A finite element method (FEM) is used to solve the structural equation of motion as well as the heat transfer equation.

Global-Local Hierarchical Analysis Techniques for Damaged Aircraft Fuselage Considering Bulging Deformation of Crack

In order to calculate the fracture parameters (Stress intensity factor) in a complicated 3- dimention aircraft model with damage in the aircraft panel, a new two steps global-local hierarchical analysis strategy is used. This paper primarily describes the development and application of advanced computational analysis techniques to determine stress intensity factors for the damaged panels based on the two steps hierarchical analysis strategy from global to 3-D local model, the bulging deformation of crack can be considered in the local model. A fracture parameter calculation programme based on automated global-local procedure to simulate cracked aircraft panel tests is developed for the hierarchical strategy. This programme may create models of two stages, transfer boundary conditions, calculate and obtain fracture parameter automatically. Finally, this paper presents some of the experimental data and the calculated fracture parameters are compared with the experimental results.

Plane wave analysis of acoustic wedges using the boundary-condition-transfer algorithm

The present work delineates the applicability of the boundary-condition-transfer algorithm for analyzing the performance of the acoustic wedge. The theoretical model, based on the plane wave acoustical coupling between two interacting ducts of variable cross-sectional area, outlines the simplicity as well as the usefulness of the current approach. The proposed model assumes bulk reaction and hence a wave propagation in the wedge material. An asymptotic solution using the Peano-Baker series of matrix calculus is derived with the aid of an inherently stable boundary condition transfer (BCT) algorithm. The proposed method is validated extensively against the available literature in order to establish the utility of this elemental approach over its much more complex and time consuming counterparts like FEM and BEM.

Modelling of the Initial Failure of Cfrp Structures by Partial Discretisation: Amicro / Macro-Mechanical Approach of First Ply Failure

The formation of transverse matrix cracks is the early failure in carbon fibre reinforced composites (CFRP). Unidirectional laminates with 90° fibre orientation were tested by transverse tensile tests and in situ under 3 point bending load in the scanning electron microscope (SEM). Finite element analysis were carried on the microscopic level hexagonal unit cell of fibre and matrix, as on the macroscopic level based on homogenized fibre and matrix properties as well. To link the micromechanical approach with the homogenized description of composite structures was done by transferring boundary conditions from one model to the other. The influence of the temperature on the Young's modulus, the non-linear stress-strain behaviour and the strength of the matrix on the micro residual stresses and matrix failure was taken into account has been investigated in detail. Process induced thermal residual stresses and matrix failure of unidirectional carbon fibre reinforced composites (CFRP).

Heat trace asymptotics defined by transfer boundary conditions

We compute the first five terms in the short-time heat trace asymptotics expansion for an operator of the Laplace type with transfer boundary conditions using the functorial properties of these invariants.

Extrusion modelling of 6061 aluminium alloy and particle reinforced MMCs

Extrusion modelling was performed for 6061 aluminium alloy and three particle reinforced MMCs (10%Al2O3/6061, 15%SiC/6061, 20%Al2O3/6061) using constitutive equations previously obtained from torsion test data. In applying the finite element software DEFORM, suitable heat transfer, friction, and velocity boundary conditions were chosen based on a direct extrusion press. Simulations were run for various extrusion conditions and the outputs for the four materials were compared. The simulation results were validated by comparison with real life extrusions and modelling of other researchers. The results showed that an increase in billet temperature, a reduction in ram speed, or a reduction in extrusion ratio had the effect of reducing the ram load. In consequence, extrusion conditions could be selected so that extrusion of the composite was carried out with the same peak ram load as the alloy.

Computer model of unidirectional solidification of single crystals of high temperature alloys

AbstractI t has been common practice to use mould withdrawal unidirectional solidification to produce single crystal castings. To grow single crystals successfully, it is important to control several solidification parameters, such as the morphology of the solidification front (solid/liquid interface), thermal gradient, and growth rate during solidification. It is the aim of this study to develop a solidification model that can predict such solidification parameters for various design and operating conditions. The solidification phenomena in the process modelled are basically controlled by two heat transfer mechanisms: conduction and radiation. A set of heat transfer equations and boundary conditions were employed to describe mathematically the heat transfer phenomena. Then the finite difference method was used numerically to solve these equations for specified boundary conditions to obtain the temperature distribution and temperature variation in the casting. The solidification parameters can subsequentl...

Calculation of Temperature Distribution in Multistage Axial Gas Turbine Rotor Assemblies When Blades Are Uncooled

Calculation of the temperature distribution in the turbine rotor of the axial gas turbine engine is an essential preliminary to a meaningful calculation of the stress distribution and the prediction of related life of the various rotor elements. Where the turbine blades are uncooled, the element of chief concern is the turbine disk, with respect to achieving acceptable life. The art of performing a multistage axial gas turbine rotor assembly temperature distribution analysis is reviewed in detail with particular emphasis on choice of heat transfer correlations and boundary conditions in the steady state. Modification of the thermal model to yield transient temperature results is discussed briefly. Comparison of analytical results with some recent engine disk temperature measurements is presented.