Measurement Techniques

Measurements in turbomachinery applications usually need to resolve small changes that will have a big impact when transferred to the real machine. Precise measurements are only possible using highly accurate measuring devices. These devices need to be adapted individually to the measuring purpose. The institute has always intensively worked in the fields of development, design, calibration, application and analysis of these measurement techniques. The great expertise enables to deliver accurate and flexible solutions for nearly all measurement challenges. The close cooperation with the institute’s mechanical workshop keeps production times short and enables to solve problems already during construction.

Unsteady pressure transducers are used to capture unsteady effects in compressors and turbines. The wall pressure is measured to analyze the flow field in the rotor tip region. Additionally, pressure probes enable measurements in the rotor or stator outlet flow.

Measuring of the exit flow in axial compressors is usually realized with instrumentation on the leading edges of the following stator vanes. These measurements are carried out stationary as well as time-resolved. The institute GLR is capable of designing, manufacturing, calibrating and commissioning of this type of instrumentation.

Five-hole probe:

  • Pneumatic concept (stationary)
  • Meassurments:
    • Total pressure
    • Static pressure
    • Mach-number
    • flowangle (2-dimensions)
  • Field of application:
    • Meassurment of flow field downstream of IGV, rotor or stator

Three-hole probe

  • Pneumatic concept (stationary)
  • Measurements:
    • Total Pressure
    • Static Pressure
    • Mach-number
    • flowangle (1-dimension)

For experimental flow investigation in turbomachinery the GLR can provide substantial experience in the application of “Particle Image Velocimetry”. The available measurement system is suitable for planar and stereo PIV. A challenge in studying turbine and compressor flow fields in the rotating rigs optical access to the field of view is crucial in terms of light sheet positioning and frame recording. Therefor the rigs are equipped with various excess possibilities in terms of window inlays in the casings. In configurations where the windows are not suitable different endoscopes and borescopes are available.

Capacitive sensors are used to measure blade vibration. Data is always recorded for safety purposes during critical operation. Afterwards, data analysis focuses on the mechanisms which lead to the observed blade vibrations.

In applied turbomachinery research beside detailed experimental determination of local phenomena a quantification of component performance is essential. Therefore the rotating rigs are equipped with specific measuring instrumentation for energetic quantification of the mechanics and fluid dynamics. In this term the large rotating rigs allow stating the current torque. Traversable pressure and temperature probes allow the flow characterization before and after the component of interest.

Oil & dye flow visualization

The method of oil & dye flow visualization is used to visualize near-wall phenomena of flows. For this purpose a mixture of binder and thinner is plotted on a surface of the region of interested (ROI). To enhance the visualization of the phenomena color particles could be added to the mixture. After plotting the mixture on the ROI the surface exposed to the flow. Due to wall shear stress effects the mixture is moved by the flow. Simultaneously the thinner starts to evaporate and the bind remains on the surface. Thus commonly accumulations of binder in regions of dead water or detachment regions are build. In regions of high flow speeds normally the binder is carried away and thus region with no color are created. The evaluation usually is done by photographically documentation.

Sketch of the test rig
Sketch of the test rig

Pressure Sensitive Paing (PSP) is an optical measurement technique used at the institute to determine film cooling effectiveness. Exciting the PSP via a light source leads to the paint fluorescing with a certain wavelength. The intensity of fluorescence depends on the partial pressure of Oxygen at the paints surface and can be measured using a camera. By using a foreign gas as a coolant film cooling effectiveness can be determined using the heat-mass-transfer-analogy.