Roberto Girardi

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.

Escoamento atmosférico no Centro de Lançamento de Alcântara (CLA): parte II - ensaios no túnel de vento

ABSTRACT: ATMOSPHERIC FLOW AT THE ALCANTARA LAUCHING CENTER (ALC): PART II- EXPERIMENTS AT A WIND TUNNEL.The atmospheric flow at the Alcantara Launching Center (ALC), which is localized near a 50 m cliff, was studied through analysis of wind tunnel (WT) experiments, using a 1:1000 geometric scale and floor level configurations to represent the cliff and its downwind roughness. The WT experiments, with 90° and 70° steps representing the cliff, both with and without additional downwind roughness, did show: (i) a perfect simulation of the ocean wind profile (a = 0.15) above the position of the step representing the cliff, through the use of a upwind carpeted fetch to provide the necessary roughness; (ii) the highest Reynolds number possible, based on the height of the cliff, was 6.52 x 10 4 inside this WT, while it reached 3 x10 7 at the ACL – thus, a more powerful tunnel is needed to simulate this last situation; (iii) the values of a nearest to the ones obtained at the ACL resulted from the 90° step experiment without any extra covering over the floor, except the upwind carpet; (iv) the fixing of cubes downwind of the step resulted roughness much greater than the ones observed over the ACL vegetation, so possibly simulating urban or industrial situations; (v) typical characteristics which occur downwind a step were simulated, such as the detachment and the posterior reattachment of the flow, plus the formation of circulation bubbles; (vi) the use of more powerful WTs would certainly permit the simulation of the atmospheric behavior of the ACL.

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.

Analysis of the Ocean Boundary Layer influence on the Mobile Tower Integration at the Alcantara Space Center

This work presents a numerical and experimental analysis of the Ocean Boundary Layer (OBL) influence on the formation of the Internal Boundary Layer (IBL) at the Alcantara Space Center (ASC), from where the Brazilian rockets are launched. The numerical simulation was carried out considering a two-dimensional flow with velocity-vorticity formulation for Navier Stokes equations. A 6th order compact finite differences scheme was used for spatial discretization and a 4th order Runge-Kutta scheme with temporal integration. The coastal cliff along the shoreline in the ASC neighborhood was specified trough the immersed boundary technique. The experimental analysis was carried out in a subsonic wind tunnel using a twodimensional Particle Image Velocimetry (PIV) system. The measurements were carried out considering the irregularity of the coastal cliff. The results confirmed that OBL height influences the height of Internal Boundary Layer that reaches the Mobile Integration Tower (MIT).

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.

Three-Dimensional Numerical Simulation of a Blowing Boundary-layer Control System

The Instituto Tecnologico de Aeronautica, ITA, in a joint with EMBRAER and the Instituto de Aeronautica e Espaco (IAE-CTA) has just finished the construction of a low-speed open circuit wind tunnel. The new tunnel is inserted into a Project of Technological Innovation supported by FAPESP (www. fapesp.br). The tunnel is now under calibration. Just after its calibration the new wind tunnel will be furnished with a boundary-layer control system. It will be a blowing system. This system usually has more than one air jet blowing into the model region. Its main function is to keep the flow two-dimensional over airfoil models. There are many variables involved in such a problem. There is need, for example, to determine the position of the air jets in respect to the airfoil and their angle. In order to access all the relevant parameters an initial two-dimensional numerical simulation is under way. The numerical simulation of the flow, inside the wind tunnel, in the blowing region will be performed using the commercial software FLUENT that has a history of great success in several aeronautical applications at EMBRAER. As a result of such an effort it will be possible to fine tune the design of the boundary-layer control system

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.

Analysis of a Methodology for 2-D High Lift Testing using a Boundary-Layer Control System by Air Blowing

This article presents an experimental methodology used to correct the flow three dimensional effects imposed by presence of the test section boundary layer on the model of an airfoil equipped with slat and flap. The methodology was carried out at the ITAs wind tunnel (Instituto Tecnologico de Aeronautica - ITA) situated in Sao Jose dos Campos (Brazil). The technique of maintaining two-dimensional flow up to the maximum lift is used to energize the boundary layer at the junction model - upper and lower walls by air blowing through the injectors in front of the model. It is analyzed a dimensionless parameter, C μ, called momentum ratio that is function of free stream Mach number, model chord, slot thickness and blowing pressure ratio. This dimensionless parameter is used to determine the blowing pressure ratios required in each attack angle of model and at several Mach number of wind tunnel free flow. Comparisons have shown good agreement between the experimental and theoretical values. Thus, the momentum ratio has indicated to be an appropriate parameter to estimate the blowing pressure ratios.

Air Intake Influence on the Test-section Flow Quality of an Open-Circuit Wind Tunnel

It is well-known that open-circuit wind tunnels are sensitive to external wind influences. The low-speed-open-circuit wind tunnel built at ITA was being more affected by these influences than it was tolerable. Therefore, the tunnel air intake was modified. The present work presents experimental data related to the impact of this modification upon the test section flow quality. It was found that the proposed solution did improve the test section flow quality to an acceptable level.