Wind Tunnels: Aerodynamics, Models and Experiments

240 Pages·2010·7.37 MB·English

by  Justin D. Pereira

ENGINEERING TOOLS, TECHNIQUES AND TABLES

W T : A ,
IND UNNELS ERODYNAMICS
M E
ODELS AND XPERIMENTS

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ENGINEERING TOOLS, TECHNIQUES AND TABLES

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ENGINEERING TOOLS, TECHNIQUES AND TABLES

W T : A ,
IND UNNELS ERODYNAMICS
MODELS AND EXPERIMENTS

JUSTIN D. PEREIRA
EDITOR

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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA
Wind tunnels : aerodynamics, models, and experiments / editors, Justin D.
Pereira.
p. cm.
Includes index.
ISBN 978-1-61942-329-9 (eBook)
1. Wind tunnels. I. Pereira, Justin D.
TL567.W5W58 2011
629.134'52--dc22
2010047058

Published by Nova Science Publishers, Inc. † New York
CONTENTS

Preface vii 
Chapter 1 Design, Execution and Numerical Rebuilding of Shock Wave
Boundary Layer Interaction Experiment in a Plasma Wind Tunnel 1 
M. Di Clemente, E. Trifoni, A. Martucci, S. Di Benedetto 
and M. Marini 
Chapter 2 The Mainz Vertical Wind Tunnel Facility– A Review of 25 Years
of Laboratory Experiments on Cloud Physics and Chemistry 69 
Karoline Diehl, Subir K. Mitra, Miklós Szakáll,  
Nadine von Blohn, Stephan Borrmann and Hans R. Pruppacher 
Chapter 3 Modeling and Experimental Study of Variation of Droplet Cloud
Characteristics in a Low-Speed Horizontal Icing Wind Tunnel 93 
László E. Kollár and Masoud Farzaneh 
Chapter 4 An Air-Conditioned Wind Tunnel Environment for the Study of
Mass and Heat Flux Due to Condensation of Humid Air 129 
Akhilesh Tiwari, Pascal Lafon, Alain Kondjoyan and
Jean-Pierre Fontaine 
Chapter 5 In-Situ Evaluation for Drag Coefficients of Tree Crowns 147 
Akio Koizumi 
Chapter 6 The Pre-X Lifting Body Computational Fluid Dynamics and Wind
Tunnel Test Campaign 167 
Paolo Baiocco, Sylvain Guedron, Jean Oswald, Marc Dormieux,
Emmanuel Cosson, Jean-Pierre Tribot and Alain Bugeau 
Chapter 7 Low-Speed Wind Tunnel: Design and Build 189 
S. Brusca, R. Lanzafame and M. Messina 
Index 221

PREFACE

This new book presents current research in the study of wind tunnels, including the
design, execution and numerical rebuilding of a plasma wind tunnel with the aim to analyze
shock wave boundary layer interaction phenomena; the Mainz vertical wind tunnel facility
experimenting on cloud physics and chemistry; an air-conditioned wind tunnel environment
for the study of mass and heat flux; using wind tunnel studies to evaluate the drag coefficient
of the tree crown and Pre-X aerodynamic/aerothermal characterization through computational
fluid dynamics and wind tunnels.
Chapter 1 - The present chapter reports the design, execution and numerical rebuilding of
a plasma wind tunnel experimental campaign with the aim to analyse shock wave boundary
layer interaction phenomena in high enthalpy conditions.
This particular flow pattern could arise in proximity of a deflected control surface, thus
generally causing a separation of the boundary layer and a loss of efficiency of the control
surface itself; moreover, high mechanical and thermal loads are generally induced at the flow
reattachment over the flap. Therefore, the analysis of this problem is crucial for the design
and development of the class of hypersonic re-entry vehicles, considering that, even though it
has been widely analyzed in the past, both from an experimental and theoretical point of
view, by describing its physical features, only few studies have been carried to analyse the
phenomenon in high enthalpy real gas and reacting flow conditions.
The activity has been developed by analysing the flow phenomenon of interest in
different conditions: i) hypersonic re-entry conditions considering the ESA EXPERT capsule
as a workbench, and ii) ground-based facility conditions considering the CIRA Plasma Wind
Tunnel “Scirocco”. The aim has been the correlation of the results predicted, by means of a
CFD code, and then measured through specific experiments suitably designed, in these two
different environments.
To this effect, a flight experiment has been designed to be flown on the EXPERT capsule
along the re-entry trajectory in order to collect flight data (pressure, temperature and heat
flux) on the shock wave boundary layer interaction phenomenon to be used for CFD
validation and, additionally, as a reference point for the extrapolation-from-flight
methodology developed accordingly. Requirements for the experimental campaign to be
performed in the “Scirocco” facility have been derived considering the most critical and
interesting points along the EXPERT trajectory. A suitable model, representative of the
EXPERT geometry in the zone of interest, i.e. the flap region, has been conceived by
defining the main design parameters (nose radius, length, width, flap deflection angle) and an
viii Justin D. Pereira
experimental campaign has been delineated, the aim being to reproduce on this model the
same mechanical and thermal loads experienced ahead and over the EXPERT full- scale flap
during the re-entry trajectory. Suitable facility operating conditions have been determined
through the developed extrapolation-from-flight methodology; the design and the analysis of
shock wave boundary layer interaction phenomenon has been done by focusing the attention
mainly to the catalytic effects over the interaction induced by the different behaviour in terms
of recombination coefficient of the materials involved in the problem under investigation.
Once defined the design loads, the model has been realized and tested in the Plasma
Wind Tunnel Scirocco under the selected conditions. The numerical rebuilding, showing a
reasonable good level of reproduction, has been also carried out, even though the validation
of the entire extrapolation-from-flight and to-flight developed methodology could be
completed only after the EXPERT flight currently planned in mid 2011.
Chapter 2 - The Mainz vertical wind tunnel is so far a worldwide unique facility to
investigate cloud and precipitation elements under conditions close to the real atmosphere.
Hydrometeors such as water drops, ice crystals, snow flakes, and graupels are freely
suspended at their terminal velocities in a vertical air stream under controlled conditions
regarding temperature (between -30°C and +30°C), humidity (up to the level of water
saturation), and laminarity (with a residual turbulence level below 0.5%) of the air stream.
Cloud processes in warm, cold, and mixed phase clouds have been investigated in the fields
of cloud physics and chemistry, aerosol–cloud interactions, and the influence of turbulence.
The experiments include the behaviour of cloud and rain drops, ice and snow crystals, snow
flakes, graupel grains and hail stones and the simulation of basic cloud processes such as
collisional growth, scavenging, heterogeneous drop freezing, riming, and drop-to-particle
conversion. Atmospheric processes have been investigated under both laminar and turbulent
conditions in order to understand and quantify the influence of turbulence.
The results are essential for applications in cloud chemistry models to estimate the
atmospheric pathway of trace gases, in cloud and precipitation models to improve the
description of the formation of precipitation (growth and melting rates), and in now- and
forecasting of precipitation to improve the evaluation of radar and satellite data.
Chapter 3 - Variation of the characteristics of aerosol clouds created in icing wind tunnels
is studied theoretically and experimentally. The characteristics of interest are the droplet size
distribution, liquid water content, temperature, velocity, and air humidity, which are among
the most important factors affecting atmospheric icing. Several processes influence the
trajectory, velocity, size and temperature of the droplets, such as collision, evaporation and
cooling, gravitational settling, and turbulent dispersion. The authors have developed a two-
dimensional theoretical model that takes these processes into account, and predicts how they
influence the changes in the characteristics of the droplet cloud during its movement in the
tunnel. The most recent development pays special attention to two of the possible collision
outcomes, i.e. coalescence after minor deformation and bounce, together with the transition
between them. Indeed, these outcomes are frequent when the relative velocity of the droplets
is small, as is the case for a cloud formed after the injection of water droplets in the direction
of air flow. An experimental study is also carried out with different thermodynamic
parameters at different positions in the test section of the tunnel, which makes it possible to
observe the evolution of cloud characteristics under different ambient conditions. The droplet
size distribution and liquid water content of the aerosol clouds were measured using an
integrated system for icing studies, which comprises two probes for droplet size
Preface ix
measurements and a hotwire liquid water content sensor. Droplet trajectories were observed
using particle image velocimetry. The experimental results are also used to validate the model
by comparing them to model predictions. Satisfactory agreement between the experimental
and calculated results establishes the applicability of the model to determine the evolution of
droplet size distribution and liquid water content in an aerosol cloud in the streamwise
direction, together with their vertical variation.
Chapter 4 - The development of an artificial ecosystem inside a closed environment is
one of the future challenging problems, which is mandatory for the long duration manned
space missions like lunar base or mission to Mars. Plants will be essential companion life
forms for such space missions, where human habitats must mimic the cycles of life on earth
to generate and recycle food, oxygen and water. Thus the optimized growth of higher plants
inside the closed environment is required to obtain efficient biological life support systems.
The stability and success of such systems lie on the control of the hydrodynamics and on an
accurate characterisation of the coupled heat and mass transfer that develop at interfaces
(solids, plants,..) within the space habitat. However, very few data can be found on the precise
characterization / prediction of the mass transfer at interfaces, and more particularly in space.
In most studies the mass flux is deduced from the measured / calculated heat flux by a heat
and mass transfer analogy.
Hence, the authors have developed a ground based experimental set-up to measure the air
flow velocities and concomitant mass transfer on specific geometries under controlled air
flow conditions (flow regime, hygrometry, temperature). The final goal is to derive a
theoretical model that could help for the prediction of the hydrodynamics and coupled
heat/mass transfer on earth, and eventually in reduced gravity. The authors have used a
closed-circuit wind tunnel for our experiments, which can produce very laminar to turbulent
flows with controlled temperature and hygrometric parameters inside the test cell. The initial
experiments have been performed in dry air with an average velocity between 0.5-2.5 m.s-1.
The velocity profiles near a clean aluminium flat plate in horizontal or vertical positions have
been studied for low Reynolds number flows by hot wire anemometry. The measurements
with the horizontal plate showed a boundary layer thickness in agreement with the Blasius’
solutions. Condensation of humid air was induced on an isothermal flat plate, which was
cooled by thermoelectricity. The mass transfer on the plate was controlled and recorded with
a precise balance. The obtained results are analyzed, and compared to the available data on
condensation.
Chapter 5 - In order to make a hazard prediction of trees against wind damage, such as
stem breakage or uprooting, it is essential to quantitatively estimate the wind force acting on a
tree. The drag coefficient of the tree crown, which is necessary to estimate wind force, has
been evaluated using wind tunnel studies. Most of the specimens used for wind tunnel studies
were dwarf trees, because of the restrictions due to wind tunnel size. However, with regard to
the wind-force response, the similarity rule is not applicable to the relationship between dwarf
trees and actual-sized trees. In fact, the drag coefficients of small trees were found to be
considerably greater than those of actual-sized trees. To estimate the drag coefficients of
actual-sized trees accurately and easily, a field test method was developed. Using this method,
wind speed and stem deflection were monitored simultaneously. The wind force acting on the
tree crown was calculated from the stem deflection; the stem stiffness was evaluated by
conducting tree-bending tests. The field tests were conducted on black poplars and a Norway
maple; the results showed that the drag coefficients decreased with an increase in wind speed.