Development of unsteady multi-hole pressure probes based on fiber-optic pressure sensors

Abstract

For measurements of unsteady flow phenomena with multi-hole pressure probes, pressure transducers are integrated in the probe near the probe tip. The application of additive manufacturing enables a wide variation in probe geometries for complex use cases. The spatial characteristics of the unsteady probe are determined by the steady state calibration in a known free-jet wind tunnel. Furthermore, the acoustic/pneumatic line-cavity system, that emerges inside the channels of the probe, is investigated in detail in the temporal calibration. In order to realize multi-hole probes with higher temporal resolution, which can be operated in harsh environments, a fiber-optic pressure sensor is developed. The measurement principle of the fiber-optic sensor is based on the Fabry-Pérot interferometer effect. The sensor is operated differentially with a pressure capillary by either pressurizing the sensor or using the surrounding static pressure as the reference pressure. Besides calibration of the sensor, comparisons with a state-of-the-art piezo-resistive pressure transducer have been performed. The focus of this work is on the reproducibility of both frequency response and amplitude.

Spatial and temporal resolution of a fast-response aerodynamic pressure probe in grid-generated turbulence

“…The probe is equipped with five differential piezo-resistive pressure sensors (Meggitt Endevco 8507C-2), which are pressurized with the ambient pressure outside of the wind tunnel as reference pressure. The sensors are surrounded with a silicone tubing and pressed into the cavities in order to avoid leakage (Heckmeier et al (2019)). The reference pressure lines of the differential transducer are merged in a manifold, so only one pressure tubing is connected to the reference pressure.…”

“…In the following, some details on the respective calibration process is given. Nevertheless, a more detailed description can be found in Heckmeier et al (2019) and Heckmeier and Breitsamter (2020). When measuring the five pressures and setting them into relation in the reconstruction process, the flow properties at the probe tip can be deduced.…”

“…Sinusoidal waves are emitted and recorded at specified frequency steps ( Δf = 20 Hz ), and hence, the amplitude ratio and the phase shift are obtained. For this study, the temporal calibration was performed for frequencies up to 10 kHz in order to compensate for resonance and attenuation effects (Heckmeier et al (2019)). Figure 4 depicts the attenuation of the five line-cavity systems of the FRAP.…”

“…In order to overcome the downsides of hot-wire probes (e.g., fragility and high calibration effort), fast-response multi-hole aerodynamic probes (FRAP) have been investigated in several research groups worldwide (see, e.g., Johansen (2001) and Kupferschmied et al (2000)). Compared to steady pressure probes, a temporal calibration of the acoustic behavior of the line-cavity system inside the probe is determined in addition to the spatial calibration (Heckmeier et al (2019)). Due to resonance and damping effects in the acoustic system and due to the outer dimensions of the probe, both spatial and temporal filtering effects of the velocity fluctuations are expected.…”

Development of an Analytic Convection Model for a Heated Multi-Hole Probe for Aircraft Applications

“…This production technique offers a higher degree of customization and the realization of more complex geometries in comparison with conventional means. Boerner and Niehuis [ 22 ] and Heckmeier et al [ 23 ] make use of additive manufacturing advantages by employing Vectoflow probes on their studies.…”