Cottbus Turbulence Experiment Facilities Germany

Facilities and equipment

Overview

  • Experiments on rotating platforms suited for applications in the geophysical context;
  • Measurement systems: stereo PIV (Dantec), Tomo-PIV (Dantec), LIF (Dantec), LDA, infrared thermography (Infratec) simultaneous thermography/PIV, LIF/PIV measurements;
  • Closed-return air pipe facility with constant temperature conditions and full optical access, 27 m long, high spatial resolution (up to 300mm) at high turbulence levels (Karman number R+=1.9×104);
  • Measurement techniques: HWA, LDA, PIV, pressure probes, surface microphones.

CoGeoF1 (Baroclinic Wave Tank)

The CoGeoF1 setup consists of a tank with three concentric cylinders mounted on a turntable. While the inner cylinder is made of anodized aluminum and cooled by a thermostat, the middle and outer ones are made of borosilicate glass. The outer side-wall of the experiment gap is heated by a heating coil that is mounted at the bottom of the outer cylinder bath. In our setup, the experiment has a free surface and a flat bottom. De-ionized water is used as working fluid. The thermally driven rotating annulus can be seen as a simple laboratory experiment of atmospheric baroclinic instability. This instability generates a highly complex and nonlinear flow that shows many similarities with irregular atmospheric flows. For large rotation frequencies the flow shows geostrophic turbulence and multiple scale interactions. Presently, the experiment is the reference experiment within the DFG-MetStröm priority program, providing data to numerical modelers.

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Specifications: inner cylinder radius Rin=45 or 70mm (in default configuration Rin=45mm), outer cylinder radius Rout=120mm, maximum liquid level H=150mm. One can arrive in the parameter domain of Rossby and Taylor numbers 0.006<Ro<51 and 104<Ta<1011.

CoGeoF2a (Inertial Wave Tank a)

Two geometries are available for the CoGeoF2 experiments (one spherical and one cylindrical). In both cases the inner and outer containers have the possibility to rotate independently. The average rotation speeds of the inner and outer containers can be adjusted to the same value and one of the container’s rotation can then be modulated in order to excite waves. For example, one can rotate the outer container with constant angular velocity Ω0, while modulating the angular velocity of the inner one as Ωin=Ω0(1+ε sin ωt), with 0<ω<2Ω0 and 0<ε<<1. The experiments allow for studies on wave-mean- and wave-wave-interactions as well as wave turbulence.

Specifications of the spherical tank: Inner sphere radius Rin=40 or 60mm (in default configuration Rin=40mm), outer sphere radius Rout=120mm. Maximum rotation velocity of the inner and outer spheres: nin,max=125 rot/min, nout,max=40 rot/min.

Specifications of the cylindrical tank: The inner cylinder can be replaced and can have different radii or shapes. In the default configuration one uses a cylinder with inclined walls (frustum) with Rin,down=100mm, Rin,up=50mm, but an inner cylinder with vertical walls and Rin=75mm is also available. The outer cylinder with radius Rout =200mm always has vertical walls. The closed domain filled with water has the maximum height H=500mm.

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CoGeoF2b (Inertial Wave Tank b)

Two geometries are available for the CoGeoF2 experiments (one spherical and one cylindrical). In both cases the inner and outer containers have the possibility to rotate independently. The average rotation speeds of the inner and outer containers can be adjusted to the same value and one of the container’s rotation can then be modulated in order to excite waves. For example, one can rotate the outer container with constant angular velocity Ω0, while modulating the angular velocity of the inner one as Ωin=Ω0(1+ε sin ωt), with 0<ω<2Ω0 and 0<ε<<1. The experiments allow for studies on wave-mean- and wave-wave-interactions as well as wave turbulence.

Specifications of the spherical tank: Inner sphere radius Rin=40 or 60mm (in default configuration Rin=40mm), outer sphere radius Rout=120mm. Maximum rotation velocity of the inner and outer spheres: nin,max=125 rot/min, nout,max=40 rot/min.

Specifications of the cylindrical tank: The inner cylinder can be replaced and can have different radii or shapes. In the default configuration one uses a cylinder with inclined walls (frustum) with Rin,down=100mm, Rin,up=50mm, but an inner cylinder with vertical walls and Rin=75mm is also available. The outer cylinder with radius Rout =200mm always has vertical walls. The closed domain filled with water has the maximum height H=500mm.

CoGeoF3 (Taylor-Couette-System)

The COGeoF3 system consists of two independently rotating concentric cylinders of radii 35mm and 70mm (radius ratio 0.5). The inner cylinder is able to rotate with a frequency of 80 Hz, the outer one is driven up to 40 Hz. This corresponds to rotation Reynolds numbers up to 106. The length of the measurement volume is 20 times that of the gap width. A unique characteristic of the CoGeoF3 Taylor-Couette-System is that the end plates are able to rotate independently to study the impact of end effects on Taylor vortices and turbulence. The temperature can be controlled very accurately (±0.2K), thus viscosity is constant and not influenced by a variable temperature. Optical access in radial direction allows for non-intrusive optical measurement techniques. The inner cylinder is equipped with a torque measurement system.

The facility provides a thermography system (1280×980 pixel) in the spectral range 7.5-14μm and temperature range -40-1200°C, a Dantec Dynamics stereo PIV system and a Dantec Dynamics volumetric velocimetry measurement system with three 2M cameras. Other measurement possibilities: Dantec LIF system, 1D and 2D Dantec LDA systems, two frequency-doubling 15 Hz YAG lasers, five 100mW Linos continous lasers, hotwires, and a calibration tunnel.

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CoLaPipeF (Large Pipe Facility)

CoLaPipeF is designed and built up to investigate highly turbulent pipe flow with particular regard to the nature of transition, turbulent structures, scaling theory and turbulent transport processes at high Reynolds numbers (up to Re = 106). One major element is the assembly of the radial blower, the three-phase motor and the frequency converter. The radial blower has a nominal power of P = 45 kW and is connected to the pipe on its suction side. The blower itself is connected to a three-phase motor with a nominal rotation speed of 2940 Hz. A frequency converter, within a control range of 1-50 Hz, effects the adjustment control. The assembly provides a flow rate of 0.05 m3/s to 2.5 m3/s and produces a maximum velocity of 80 m/s at the contraction exit with low turbulence intensity level, i.e less than 0.4%. The maximum velocity that can be achieved with the experimental setup corresponds to 0.22 Mach number, avoiding any compressibility effects. Aiming at a stable test facility, the centrifugal blower is installed at the end of the pipe test section and it delivers its output directly to a 340 mm-diameter return line through a heat exchanger. The pipe test section contributes mostly to the total pressure loss of the facility. A cooling system is installed in order to keep the temperature constant inside the pipe test section.

The pipe diameter of the suction side of the facility is made of a high-precision smooth Acrylic-glass tube, having an internal diameter Di of 189.7±0.23 mm (i.e. a relative error of 0.12%) and total length of 27 m, providing a test section L/D≤ 140.

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Specifications: Fluid mechanical parameters: Mean velocity: U ≤ 80 m/s, mean based Reynolds number: Rem ≤ 106, wall friction velocity: uτ ≤ 3 m/s, Kármán number: R+ = 1.9×104, Working fluid: Air; geometrical parameters: L/D = 142, surface roughness: e = 5 mm; Pipe material: Acrylic glass

Measurement systems: Hot-wire anemometers, pressure probes, DPT 6000 Barometer, Prandtl tubes, stereo and volumetric PIV systems,  LIF system, 1-d and 2-d LDA systems, hotwire and calibration tunnel.