Marcelo Assato

Turbulent Flow in Wavy Channels Simulated with Nonlinear Models and a New Implicit Formulation

This work examines the performance of linear and nonlinear eddy-viscosity models when used to predict the turbulent flow in periodically sinusoidal-wave channels. Two geometries are investigated, namely a converging-diverging channel and a channel with concave-convex walls. The numerical method employed for the discretization of the equations is the control-volume method in a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm is used for correcting the pressure field. The classical wall function and a low Reynolds model are used to describe the flow near the wall. Comparisons between those two approaches using linear and nonlinear turbulence models are done. Here, a new implicit numerical treatment is proposed for the nonlinear diffusion terms of the momentum equations in order to increase the robustness. Results show that by decomposing and treating terms as presented, solutions using nonlinear models and the high Reynolds wall treatment, which combine accuracy and economy, are more stable and easier to be obtained.

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.

Flow and Heat Transfer Past a Sudden Contraction With a Porous Insert Using Linear and Non-Linear Turbulence Models

This work presents a numerical investigation for the turbulent flow and heat transfer in an abrupt contraction channel with a porous material placed in a flow passage. The channel has a contraction rate of 3:2. Results for the hybrid medium were obtained using linear and non-linear k-e macroscopic models. It was used an inlet Reynolds number of Re = 132000 based on the height of the step. Parameters such as porosity, permeability and thickness of the porous insert were varied in order to analyze their effects on the flow pattern. The results of local heat transfer, friction coefficient and stream lines obtained by the two turbulence models were compared for the cases without and with porous insertion of thickness a/H=0.083, 0.166 and 0.250, where H is the step height. Insert porosity of varied between 0.85 and 0.95 with permeability in the range 10−6 –10−2 m2 .Copyright

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.

Heat Transfer in a Suddenly Expanded Turbulent Flow Past a Porous Insert Using Linear and Non-Linear Eddy-Viscosity Models

This work presents numerical results for heat transfer in turbulent flow past a backward-facing-step channel with a porous insert using linear and non-linear eddy viscosity macroscopic models. The non-linear turbulence models are known to perform better than classical eddy-diffusivity models due to their ability to simulate important characteristics of the flow. Parameters such as porosity, permeability and thickness of the porous insert are varied in order to analyze their effects on the flow pattern, particularly on the damping of the recirculating bubble after the porous insertion. The numerical technique employed for discretizing the governing equations is the control-volume method. The SIMPLE algorithm is used to correct the pressure field. Wall functions for velocity and temperature are used in order to bypass fine computational close to the wall. Comparisons of results simulated with both linear and non-linear turbulence models are presented.© 2002 ASME

Simulation of Axial Flow in a Bare Rod Bundle Using a Non-Linear Turbulence Model With High and Low Reynolds Approximations

This work presents a numerical investigation of fully developed turbulent flow in a triangular sub-channel of a bare rod bundle using a Non-Linear Eddy Viscosity Model (NLEVM). The numerical technique employed for discretizing the governing equations is the control-volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to correct the pressure field. The classical wall function and a low Reynolds model were used in order to handle flow calculations near the wall. In this work, the influence of constants of calibration existing in the non-linear terms of the model is analyzed.© 2002 ASME

Effect of Tangential Blowing on Two Dimensional Boundary Layer of a Wind Tunnel

This paper reports an experimental effort to investigate the influence high-pressure air jet on the boundary-layer of the research low–speed wind tunnel of the Instituto Tecnologico de Aeronautica (ITA). Boundary layer control is very important in two-dimensional airfoil model tests. This may be done by either suction or blowing of the boundary layer. At ITA it was decided to blow high energy air into the test section. The literature reports that tunnel wall boundary-layer control, at the wall-model junctions, is necessary in order to obtain useful results from two-dimensional high-lift tests in wind tunnels. Here, it is shown results of the interaction of several configurations of the air jet with the wind tunnel boundary layer. Three injector thicknesses were used 1.0 mm, 1.5 mm and 2.0 mm. The angle was either of 10 o or 20 o . Boundary layer measurements were obtained using a pressure rake. It was positioned at eight stations along the test section, X1=10 cm, X2=16 cm, X3 =22 cm, X4= 28 cm, X5= 34 cm, X6= 40 cm, X7= 50 cm e X8= 60 cm measured from blower slot. The free stream dynamic pressure was kept constant, q∞ = 325 mmH2O.

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.

Turbulent Flow and Heat Transfer in a Porous Chamber

This work presents a numerical investigation of turbulent flow past a porous structure in a channel using linear and non-linear eddy viscosity macroscopic models. Parameters such as porosity and permeability of the porous material are varied in order to analyze their effects on the flow pattern, particularly on the damping of the recirculating bubble after the entrance and exit regions. The numerical technique employed for discretizing the governing equations is the control-volume method. The SIMPLE algorithm is used to correct the pressure field. The classical wall function is utilized in order to handle flow calculation near the wall. A discussion on the use of this technique for simulating the flow in question is presented. Comparisons of results simulated with both linear and non-linear turbulence models are shown.Copyright