University of Bologna - Polo Scientifico Didattico di Forlì: Center for International Cooperation in Long Pipe Experiments (CICLoPE)
| Organisation: | University of Bologna |
|---|---|
| Location: | Bologna, Italy |
| Website: | http://www.ciclope.unibo.it |
| Contact: | Alessandro Talamelli |
Summary
- large scale wind tunnel (0.9mØ) to generate turbulent scales fully resolvable with currently available measurement techniques
- fully developed turbulence at high Reynolds numbers in naturally generated flow (120m long)
- full and easy access to the test section
- highly controlled environmental conditions (no background noise, stable temperature and humidity)
The infrastructure allows the worldwide best space and time resolved measurements in turbulent flows achievable in wind tunnels. It is perfectly suited for testing and optimizing novel measurement techniques and may be easily adopted to study various aspects of turbulent flows, e.g. pressure gradients, wall roughness and friction control.
The Center for International Cooperation in Long Pipe Experiments (CICLoPE) is a research laboratory which allows high resolution turbulent-fluctuation and detailed flow structure measurements. The laboratory is operated with the idea of gathering world-leading scientists in the field of turbulence research for a closely coordinated collaborative effort to make decisive breakthroughs in the fundamental issues of high Reynolds number turbulence.
The centre was founded and it is presently lead by a group of different Universities and research Centres: the University of Bologna, the International Centre of Theoretical Physics in Trieste, the Royal Institute of Technology, Illinois Institute of Technology and Ecole Polytechnique Fédérale de Lausanne, the University of Rome La Sapienza and Princeton University.
The laboratory is located beside the old factory of the Caproni Industry, which is basically a tunnel complex excavated in order to provide both shelter for civilians, and make the plant operative even under bombing activities. In 2006 the tunnels were given by the Air Force to the University of Bologna specifically for turbulence studies. The complex comprises two 130 m long tunnels with a diameter of about 9 m each. The stability of the ambient conditions, viz. temperature, humidity; the complete absence of any background noise (vibration, electrical noise, etc.) are the characteristics that makes Predappio an ideal site for this laboratory.
The main facility that will be used (the Long Pipe) is basically a closed loop wind tunnel operating with air at atmospheric pressure. A closed loop has been chosen since it will allow the flow characteristics to be accurately controlled in terms of velocity, temperature and humidity. The layout resembles an ordinary wind tunnel where the main difference is the long test section which gives most of the friction losses. Many of the various aerodynamic components are the same as those for an ordinary wind tunnel (diffusers, screens, contraction, etc.). The long pipe consists of a 115 m long tube with an inner diameter of 0.9 m and will be made of 5 m long carbon fiber modules held by precision positioning elements.
To allow detailed flow structure measurements and high resolution turbulent-fluctuations measurements it will be of utmost importance to equipe CICLoPE with a specific laboratory for the design and manufacturing of home made miniaturized probes which can be used to fully characterised the turbulent scales. Commercial probes are in fact not appropriate to investigate this type of flow either because they are too big for the required resolution or because they are subjected to too strong interference effects. The facility is also designed in order to easily host devices for turbulence generation/manipulation to enhance the natural turbulence development or to produce a predetermined turbulent flow.
The definition of the Reynolds number shows that various possibilities exist to obtain high Re, the velocity (U) should be high (but not so high that compressibility effects come into play), the density can be increased (by for instance pressurizing an air flow facility) or the physical dimensions (L) should be large. On the other hand, for the type of studies aimed at, it is necessary to have a facility where the spatial size of the smallest scale is sufficiently large to be resolvable by available measurement techniques. A measure of the smallest scale is the viscous length scale, l*, and it can easily be shown that for a pipe flow experiment with high Reynolds number, in order to keep large (and measurable) scales, l*, the diameter of the facility should be chosen as large as possible. Concerning the geometry to be used in the experiment, a unique advantage of the pipe flow compared to all the other canonical cases is that the wall shear stress can be determined directly from the pressure drop along the pipe, which can be measured accurately.
Over the years, there have been a number of pipe flow experiments reported in the literature, but they are mainly at low Reynolds numbers and do not fulfil the criteria above. In the Princeton super pipe the high Reynolds number is obtained through highly pressurizing the air used, reaching Reynolds numbers R+ of up to 500.000. Although the Reynolds numbers that are achieved in the super pipe are extremely high for a laboratory experiment it is at the expense of a very small viscous length scale, i.e., for R+=500000 the viscous length l* is only slightly above 0.1 µm. The scientific results from the super pipe include measurements of the mean velocity distribution and new information on the skin friction variation for both smooth and rough surfaces. However, due to the spatial resolution limitations, few reliable turbulence data have been published.
Range of parameters that can be reached by CICLoPE compared with other from international facilities
The Long Pipe is designed to provide a test rig for at least twenty years of basic research in this field. It will also offer the external users the possibility for extensions with more direct impact on applications, such as the study of the effect of non-smooth walls or non-isothermal conditions, the evolution of various non-equilibrium flows, and of flows with some particulates.
The laboratory is presently still under construction. The facility is planned to be completed and tested by the end of year 2008. The access will be available to external users by the beginning of 2009.