Abstract:This contribution gives an overview of the current state, performance, and limitations of the fast-response aerodynamic probe measurement system developed at the Turbomachinery Lab of the ETH Zurich. In particular, the following topics are addressed:
• Probe technology: Miniature probes with tip diameter ranging from 0.84 to 1.80 mm (one-sensor and three-sensor probes, respectively) have been developed. New technologies derived from microelectronics and micromechanics have been used to achieve … Show more
“…A miniature pressure sensor chip of piezoresistive type is mounted in the probe. This probe has a tip diameter of 1.8 mm and is described in detail in Kupferschmied et al, 22 Roduner et al, 23 and Koeppel et al 24 In terms of the systematic fluctuations, this probe provides two-dimensional velocity and total and static pressure in steady and periodically unsteady flows. Figure 3.Tip of flow measuring probe.…”
Section: Experimental Facility and Instrumentationmentioning
To see the tip clearance effect on a centrifugal compressor, time-resolved flow measurements are carried out at the discharge of a centrifugal compressor impeller with a diameter of 280 mm. The impeller is 30 back swept and is operated at a blade tip speed of 260 m/s, which is a rather high speed for measuring time-resolved flow. Six levels of tip clearance ratio ranging from 0.06 to 0.21 were tested. A fast response aerodynamic probe equipped with a single pressure sensor is used for the flow measurements. The correlation between the impeller efficiency and the tip clearance is presented. The mean flow variation from hub to shroud is obtained and its dependence on the tip clearance is discussed. The measured time-resolved flow at impeller exit differs from the classical jet-wake flow model. Four kinds of flow patterns (blade wake, jet, channel wake, and tip clearance flow) are observed at the impeller discharge plane. By increasing the tip clearance, the total pressure loss in the vaneless diffuser decreases, while the impeller loss increases. One-dimensional flow calculations of the vaneless diffuser show that the matching constant of a skin friction coefficient is decreased by increasing the tip clearance.
“…A miniature pressure sensor chip of piezoresistive type is mounted in the probe. This probe has a tip diameter of 1.8 mm and is described in detail in Kupferschmied et al, 22 Roduner et al, 23 and Koeppel et al 24 In terms of the systematic fluctuations, this probe provides two-dimensional velocity and total and static pressure in steady and periodically unsteady flows. Figure 3.Tip of flow measuring probe.…”
Section: Experimental Facility and Instrumentationmentioning
To see the tip clearance effect on a centrifugal compressor, time-resolved flow measurements are carried out at the discharge of a centrifugal compressor impeller with a diameter of 280 mm. The impeller is 30 back swept and is operated at a blade tip speed of 260 m/s, which is a rather high speed for measuring time-resolved flow. Six levels of tip clearance ratio ranging from 0.06 to 0.21 were tested. A fast response aerodynamic probe equipped with a single pressure sensor is used for the flow measurements. The correlation between the impeller efficiency and the tip clearance is presented. The mean flow variation from hub to shroud is obtained and its dependence on the tip clearance is discussed. The measured time-resolved flow at impeller exit differs from the classical jet-wake flow model. Four kinds of flow patterns (blade wake, jet, channel wake, and tip clearance flow) are observed at the impeller discharge plane. By increasing the tip clearance, the total pressure loss in the vaneless diffuser decreases, while the impeller loss increases. One-dimensional flow calculations of the vaneless diffuser show that the matching constant of a skin friction coefficient is decreased by increasing the tip clearance.
“…Humm et al [5] studied various probe shapes and geometric parameters regarding their intrusive influence in flow fields. Further investigations based on the two aforementioned studies show the application of a fast-response cylinder probe in a centrifugal compressor [6][7][8]. Moreover, Rediniotis et al [9] built a MEMS based fast-response five sensor probe for subsonic measurements, in order to test the angular/spatial and temporal characteristics of the probe with signal frequencies of up to 400 Hz.…”
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.
“…The probe's measurement chain consists of the sensing elements, power supply units, signal conditioners, a 14-channel 24 bit analog-to-digital converter (sampling at upto 500 Hz) and an on-board flash card for data storage. The aerodynamic calibration of the probe was carried out in a fully automated free-jet facility at ETH Zurich [18], and yields less than 0.1% relative error in angles and dynamic pressure. The drone's on-board autopilot system, which is based on Paparazzi [19], is used for fully autonomous flight.…”
a b s t r a c tThe wake evolution measured downstream of multi-megawatt wind turbines located in flat and complex terrains are described here. These high-resolution measurements at full-scale Reynolds number conditions are made with an instrumented drone that is equipped with a suite of sensors and detail the characteristics of the mean flow and turbulent kinetic energy in the evolving wake. Reynolds decomposition yields the nature of turbulent fluctuations in surface layer, and this decomposition is used to detail the turbulence statistics, degree of anisotropy and friction velocity. These measurements are shown to be suited for the further development of three-dimensional wake models that are currently under intensive development.
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