Large-size pitot probes (diameters 10-20mm) are necessary for turbine blade flow field testing, where measuring high-volume, low-speed airflow requires sufficient sensor area, but their size introduces unique challenges.5-Hole Pitotwelcome to click on the website to learn more!
Structural rigidity is paramount, as turbine blade passages can generate vibrations up to 500Hz. Probes with a stem length-to-diameter ratio (L/d) of 8-10 balance rigidity and flow disturbance—an L/d of 12 or higher may cause bending in turbulent flow, leading to measurement errors. In a power plant turbine test, a long, slender probe (L/d=15) showed 4% more pressure fluctuation than a stiffer model (L/d=8).
Material choice depends on temperature: for gas turbines (300-600°C), Inconel 718 is reliable; for steam turbines (saturated steam at 180-300°C), 316 stainless steel resists corrosion from moisture. A steam turbine test found that a carbon steel probe corroded after 200 hours, while a 316 probe remained intact for 1000+ hours.
Installation must account for the probe’s size to avoid blocking airflow. Mounting at a 30° angle to the blade surface reduces blockage by 30% compared to a perpendicular mount, as observed in a wind tunnel simulation of turbine flow. Additionally, using multiple small holes (4-6) instead of one large hole distributes pressure sampling, improving accuracy in non-uniform flow.
Calibration for large probes should include checking for flow blockage effects, which can artificially increase measured pressure by 2-3% in narrow blade passages. This involves comparing readings with smaller probes in the same location and applying a correction factor based on the blockage ratio (probe area vs. passage area).