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Heat Transfer Studies in the Flow Over Shallow Cavities

Fluid flows along a shallow cavity. A numerical study was conducted to investigate the effects of heating the floor of the cavity. In order to draw a broader perspective, a parametric analysis was carried out, and the influences of the following parameters were investigated: (i) cavity aspect ratio, (ii) turbulence level of the oncoming flow, and (iii) Reynolds number. A finite-difference computer code was used to integrate the incompressible Reynolds-averaged Navier-Stokes equations. The code, recently developed by the authors, is of the pressure-based type, the grid is collocated, and artificial smoothing terms are added to control eventual odd-even decoupling and nonlinear instabilities. The parametric study revealed and helped to clarify many important physical aspects. Among them, the so called vortexes encapsulation, a desirable effect, because the capsule works well as a kind of fluidic thermal insulator. Another important point is related to the role played by the turbulent diffusion in the heat transfer mechanism.

NUMERICAL SIMULATION OF THE INCOMPRESSIBLE NAVIER–STOKES EQUATIONS

A scheme for the numerical simulation of incompressible flows is presented. The modeling equations are written in conservation law form. The algorithm, written in a delta form, is very robust without resorting to any degree of relaxation. The well-known cumbersome numerical implementation related to staggered grids is totally removed. The scheme is second-order-accurate in space and first-order in time. An important novelty is the separation of the pressure terms in the physical equations in a pressure flux, facilitating the tackling of different fluids. The algorithm has been applied to laminar and turbulent flows. The results are truly encouraging.

Three -dimensional Flow Over Shallow Cavities

An experimental study was conducted to investigate the flow over a shallow cavity. A parametric analysis was carried out, and the influences of the cavity aspect ratio and of the Reynolds number were investigated. The f low mapped along longitudinal planes by means of Particle Image Velocimetry. The parametric study revealed and helped to clarify many important physical aspects. Nomenclature le = entrance characteristic length ls = exit characteristic length s = cavity d epth w = cavity length Re s = Reynolds number based on the cavity depth

Calibration of a Boundary-Layer Control System for Use in a Low-Speed Wind Tunnel

The present work presents an experimental investigation of the jet flow produced by a blowing system for boundary-layer control at the test section of a low-speed wind tunnel. The main objective is to verify the flow uniformity at the system exit. The air jet leaving the apparatus was varied by changing the exit jet thickness as well as its inclination. The first measurements showed a very significant flow distortion. After a through and systematic work the desired flow uniformity was obtained.

Research Wind Tunnel of the Aeronautical Institute of Technology: Conceptual Design and Calibration

The objective here is to describe ITAs wind tunnel conceptual design and to report the tunnels preliminary calibration results. The open- circuit wind tunnel has a 1.0mx1.2m test section. The maximum velocity is approximately 80 m/s and the turbulence level, according to the design requirements, should be less than 0.05% at the maximum velocity. An eight-blade fan, run by a 200hp electric motor, generates the flow. The wind tunnel entrance nozzle is located inside Prof. Feng Aeronautical Engineering Laboratory. The test section is designed to be very flexible, in order to reduce the time and cost for mounting new experimental apparatus. The tunnels exit section is connected to an element, where the flow is deflected upwards. Such procedure was adopted to minimize the atmospheric wind variations effect on the test section flow. The preliminary calibration results show that the turbulence level is much higher than the ambitious design, at least when no filter is used. The authors believe that there may be a strong influence of vortexes generated at the labs entrance. The new wind tunnel will be used, in the near future, in two research programs proposed by EMBRAER. After these programs are over it will continue to be a very important research tool for ITA and EMBRAER.

Experimental Study of the Turbulence Level at the Intake of an Open Circuit Wind Tunnel

In the planning and design of a new wind tunnel the choice between closed and open-circuit types is a very important one. If on one hand the open –circuit solution is attractive for its low price and continuous fresh test air, on the other hand the test section flow quality is potentially affected by external winds. This sensitivity becomes especially critical at low-test speeds. Although many open-circuit wind tunnels have been built, there have been some problems either of low operating efficiency or sensitivity to external winds, or both. In this respect both ends of the tunnel are objects of concern. In the present paper, however, the authors concentrate their attention to the wind tunnel inlet section. At the Instituto Tecnologico de Aeronautica a non-return wind tunnel is currently under design. The test section flow quality requirements are very strict and the test-section turbulence level is to be as low as 0.05% of the mean flow kinetic energy. To insure that the desired turbulence level and flow uniformity at the test section is achieved the tunnel will have a 10:1 contraction, a honey comb and three screens with provision for an extra one. Further, the 35meter long facility has its inlet section, the contraction and the test section inside a 25x10 room. The diffuser, the fan section and the exit section are mounted outside the laboratory room. Figure 1 shows the tunnel layout. Although its position inside the laboratory is beneficial as does not expose the inlet section directly to the outside wind it also arises following concerns: (i) to operate the wind tunnel a large 6mx2.5m door will have to be open. Both side ends of this door will generate a shear layer exactly in front of the facility air intake (ii) the tunnel inlet section is not symmetrical in respect to the laboratory’s walls, being much closer to the one on its right-hand side. The 3.8m wide by 3.16 m high inlet is only about 20 cm away from both the floor and the ceiling of the room. In order to quantify these influences on the mean velocity distribution and on the turbulence level, at the tunnel air intake, an experimental study was made on a 1/10 scale model of the part of the tunnel to be built inside the lab.

On the Calculation of an UAV's Response to Elevator Deflection

[Abstract] UAVs are becoming more and more importan lately due to the declining costs of the electronic systems needed to guide them. This type of aircraft has many interesting applications specially substituting manned aircraft in dangerous missions such as transmission lines inspection. In the particular transmission line concerning the authors the hilss and trees along the way are of concern. To accomplish the mission the airplane has to cruise at approximately 80km/h. Thus, it is very important to gather lowReynolds number data. This is a very interesting and not fully understood flow regime. This work presents experimental data for the following aerodynamic coefficients: Lift, drag and pitching moment as a function of the angle of attack and of the horizontal tail incidence. The experimental results allowed calculations of the flight dynamics of the aircraft, and comparisons with theoretical methods to predict the aerodynamic forces for flight simulations.

Multi-point Wing Design of a Transport Aircraft Using a Genetic Algorithm

‡The present work deals with the optimization of transonic airfoils, subjected to a set of constraints, such as maximum thickness t/c and off-design conditions. In this work, a linking was made between an optimizer based in genetic algorithm, BLWF a numerical code to calculate the flow around the wing-fuselage, and module to generate the aircraft geometry. The wing was generated by 3 main airfoils, and each one was represented by 2 equations. Results were generated for Mach numbers between 0,76 and 0,79 using a representative fuselage of a 70-passenger aircraft. One of the major advantages of numerical optimization is the reduction in design time, while dealing with a wide variety of design variables and constraints which are difficult to visualize using graphical or tabular methods. The objective function aimed the maximization of ML/D for the chosen Mach number.

Design of the ITA's Research Wind Tunnel Contraction Using CFD Tools

The present work describes the conceptual design of the contraction for the new subsonic research wind tunnel being constructed at the Technological Institute of Aeronautics (ITA), located in S ao Jos e dos Campos, Brazil. The contraction was conceived to yield an excellent flow quality at the test section. The method described by Morel was used to design a set of reasonable initial geometries, which were labeled and organized in some groups. The fully unstructured CFD code FLUENT was then employed to analyze the flow inside of some selected wind-tunnel configurations. The CFD results clearly revealed the most suited configuration regarding the required characteristics at the test section. The study is part of a project of technological innovation being supported by FAPESP in which ITA and Embraer are involved. The final objective of this endeavor is to create a methodology for extrapolation of experimental 2-D results to threedimensional configurations.

Aerodynamic Analysis of a Re-Entry Capsule

The present work deals with the contribution of DLR (Deutsches Zentrum fur Luftund Raumfahrt) to the IAE s SARA project in the area of aerodynamics. The objective of the study is to investigate the viscous effects and the influence of the angle attack on the base flow of the reentry capsule SARA. The initial points for the discussion are Euler simulations and laminar Navier-Stokes calculations. They are performed with the DLR Euler and Navier-Stokes code TAU applying unstructured grids.