Fluid mechanical processes govern the performance of industrial goods, noise emissions, power consumption and energy conversion. Our work combines fundamental research in fluid mechanics, theory, experiments and numerical simulation with application areas in aerospace, automotive and energy technologies.
Several commercial PIV systems are available for quantitative flow field measurements. Most PIV variants can be built if the components are suitably arranged. Research and development is mainly done with standard 2C2D, stereo 3C2D and high-speed PIV. All components, i.e., lasers, cameras, sequencers, and the necessary software, as well as the necessary experience, are available at the institute to study all kinds of flows with PIV.
The components can also be used in related optical methods. In particular, these shadowgraphy for determination of droplet size and shape, planar laser-induced fluorescence (pLIF) for determination of temperature or concentration fields in liquids, and the use of pressure sensitive paints (PSP).
To visualize density, or - to be more precise - density gradient fields, classical Schlieren methods are used, in particular the Single Mirror Coincident Schlieren technique, Focused Schlieren, but also the Background Oriented Schlieren (BOS) method. Schlieren methods are typically used for highly compressible flows (supersonic or hypersonic flows or flows with strong vortices) which are also very dynamic in nature. Therefore we would typically combine the Schlieren-optics with one of the high-speed cameras. Depending on the required resolution and field of view, recording rates starting from 1 kHz up to 80kHz can be realized.
Some features of wall-bounded flows can be visualized from the surface temperature distribution. For such visualization we use a commercial thermography system (infrared camera), which is based on a sterlin-cooled InSb-sensor and allows acquisition rates of 300 frames per second at a resolution of 640 x 512 pixels. The camera is often used for more qualitative visualizations, e.g. laminar turbulent transition, but can also be used to quantitatively reconstruct the heat flux from the spatial and temporal temperature evolution, even if a lateral heat flux exists. The corresponding software was developed at ISM.
Thermal anemometry allows to determine single (or multiple) components of the velocity with a very high temporal resolution. Various commercial bridge systems are available for this purpose, which can be used in air or water. Due to the temporal resolution, thermal anemometry is typically used if highly dynamic and/or spectral information is required. The systems at ISM can be used either for measurements in free flows (so-called hot wire anemometry) or for measurement of wall shear stress on a surface (so-called surface hot films). The hot wires can be calibrated in a special calibration wind tunnel for a quantitative measurement. Hot-wire measurements are mostly used to measure the properties of transitional boundary layers (e.g. stability analysis, amplification rates) or turbulent quantities. With special calibration and evaluation techniques, thermal anemometers can be used at ISM for turbulence measurements in all flow regimes, from low subsonic flows (<10m/s) up to hypersonic flows (Ma=6).
The measurement of static and total pressures is an almost obligatory element of any fluid mechanical or aerodynamic measurement. The ISM has modern multi-channel pressure scanners available, which are very modular and can be configured for a wide variety of measurements. Through years of experience in cooperation with the model and prototype manufaction in the central workshop, we can fabricate pressure taps and/or insert pressure probes in all possible and impossible places. We have a comprehensive equipment of probes (Pitot-, Prandtl-, five-hole probes). For airfoils, a traversing wake rake and a modular analysis software to derive drag coefficients are available. To measure high-frequency pressure disturbances, a number of fast-response pressure scanners can be used. In hypersonic flows, high-precision PCB pressure sensors can also be used.
Digitalization of an ice shape is often regarded very challenging due to the complexity of the ice geometry, as well as the optical properties of ice. An approach used by the ISM for this task is the photogrammetry method. This method consists on taking several photos of an ice shape from different angles and positions. Then, these photos are loaded into a program that proceeds to reconstruct a virtual geometry based on the common details that multiple photos present. The final product is the digitalized ice shape, which can be subsequently used for research and statistical analysis.
Force balances are essential instruments used to directly measure aerodynamic forces and moments in a variety of applications, including aircraft models, wing sections, and vehicle models. These balances can be broadly classified into two categories: Sting balances and block balances. The ISM is equipped with both types, offering a wide range of high-accuracy force and moment measurement capabilities spaning from 10 N up to 4000 N of force. One of ISM's advanced instruments is the RUAG six-component balance, a versatile device that can function as either an internal or external balance depending on the model's scale. Additional specialized balances include the Unterflurwaage KME4, used for vehicle model testing and as a three-component balance on turntables for half-wing configurations; the Große Heckstiel-Waage W611, used for complete aircraft model measurements; and the Miniatur-Stielwaage W637, typically employed in the MAV Lab to assess aerodynamic forces on micro air vehicles (MAVs). A K6D40 balance is used for laboratory courses, teaching and live demonstrations.