Mixed convection in a channel partially filled with metal foam blocks

The present work is a numerical simulation of the mixed convection of an incompressible fluid in a horizontal channel under sun radiation partially filled with metal foam blocks. The Darcy-Brinkman model is adopted. The control volume approach is used to solve the motion and energy equations governing mixed convection. The study focuses on the effect of certain control parameters such as the Rayleigh number (Ra), the thermal conductivity ratio and the porosity on the flow structure and heat transfer. Indeed, the results for flow structures and temperature distribution are presented in the form of velocity fields with streamtraces and isotherms, while the average Nusselt number (Nu) is used to quantify heat transfer.

Experimental investigation of a helicopter rotor with Gurney flaps

ABSTRACTThe present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach.

MODELING ATMOSPHERE COMPOSITION AND DETERMINING EXPLOSIBILITY IN A SEALED COAL MINE VOLUME

Explosions originated from or around the sealed areas in underground coal mines present a serious safety threat. The explosibility of the mine atmosphere depends on the composition of oxygen, combustible and inert gases. In additional, the composition in the inaccessible sealed areas change with time under various factors, such as gases emissions, air leakage, inert gases injected, etc. In order to improve mine safety, in this paper, a mathematical model based on the control volume approach to simulate the atmosphere compositions is developed, and the expanded Coward explosibility triangle diagram is used to assess the mine gas explosion risk. A computer program is developed to carry out the required computations and to display the results. In addition, the USBM explosibility diagram is also included in the program to serve as a double check.

A Control-Volume Model of the Compressible Euler Equations with a Vertical Lagrangian Coordinate

Accurate and stable numerical discretization of the equations for the nonhydrostatic atmosphere is required, for example, to resolve interactions between clouds and aerosols in the atmosphere. Here the authors present a modification of the hydrostatic control-volume approach for solving the nonhydrostatic Euler equations with a Lagrangian vertical coordinate. A scheme with low numerical diffusion is achieved by introducing a low Mach number approximate Riemann solver (LMARS) for atmospheric flows. LMARS is a flexible way to ensure stability for finite-volume numerical schemes in both Eulerian and vertical Lagrangian configurations. This new approach is validated on test cases using a 2D (x–z) configuration.

Numerical Simulation of the Aerodynamic Behavior of Propeller Blades at Subsonic Conditions

The Organization of the Petroleum Exporting Countries (OPEC) oil crisis of the mid 1970s led to a revival in interest in the propeller as a possible fuel-efficient propulsion for aircraft operating at subsonic cruise speeds. A propeller aerodynamics is complex and should be analyzed carefully to ensure maximum propellers efficiency. Detailed knowledge of flow patterns and aerodynamics loads is necessary for blade material and manufacturing process. In this study, an isolated propeller blade is chosen as the base of analysis, the geometry of the propeller: twist and chord variation with radius, are taken from real case module. The boundary conditions of the computational domain are set corresponding to that exist in the propeller manuals. A three dimensional unstructured grid was generated and adopted using commercial grid generator GAMBIT software. The governing equations are solved using FLUENT6.3.26 a commercial CFD code, which uses a control volume approach on a grid over the computational domain. Results identified that the propeller efficiency, power coefficient are increases to reach maximum values and then decreases with increase Mach number. The thrust coefficient decreases with increase Mach number.

Theoretical flowrate characteristics of the conjugated involute internal gear pump

The aim of this article is to study the theoretical flowrate characteristics of the conjugated involute internal gear pump. The conjugated involute internal gear pump has a different internal gear, the profile of which is completely conjugated to that of pinion, from the conventional involute internal gear pump. To describe briefly, the former pump is called ‘conjugated pump’ while the latter pump ‘conventional pump’. This structure makes the conjugated pump have smaller volumes of trapped fluid than the conventional pump, which indicates the conjugated pump has a better flowrate performance. Although there have been numerous investigations into gear pumps, none of them have dealt with the conjugated pumps yet. This article presents a systematic study on the theoretical flowrate characteristics of the conjugated pumps. It is expected to obtain some generalized conclusions to guide the design of internal gear pumps. Firstly, a double envelope concept is applied to derive the mathematical models of the conjugated involute internal gear couple. Next, mesh characteristics of the gear couple, which mainly decide the fluid delivery performance of the pumps, are analyzed. Finally, using a control volume approach, the theoretical flowrate characteristics of the pump under different design parameters of gears are investigated. Results show the conjugated pump has a better performance than the conventional one. To design a conjugated pump with good flowrate characteristics, it’s feasible to choose a proper shifting coefficient, a larger tooth number of the pinion, a smaller tooth number of the internal gear, a larger pressure angle and a larger fillet radius, under the condition that no tooth interference occurs.