Comparison of Transient Response of Pressure Measurement Techniques with Application to Detonation Waves

摘要

During the testing of a Rotating Detonation Engine coupled with an ejector, pressure measurements indicated a deficiency in the understanding of the pressure probes. The pressure histories came from an array of Infinite Tube Pressure (ITP) static probes, Capillary Tube Average Pressure (CTAP) static probes, and direct Kiel stagnation pressure probes. Upon examination of the pressure histories, the average of the Kiel probe pressure over several laps of detonation, it was revealed that the ITP static pressures measured higher than the Kiel stagnation pressures both within the mixing chamber and at the exit of the ejector. This research conducts an unsteady calibration of the different probe configurations in order to quantify the unsteady response of the probe configurations. The unsteady calibration allows the pressure at the entrance of the probes to be reconstructed from the recorded pressure histories. The unsteady calibration of the pressure probes was performed by subjecting each of the probes to a single detonation in a detonation tube. The pressure history of a planar detonation such as the one in a detonation tube is well understood, and accurately modeled by the Zeldovich-vonNeumann-Doring (ZND) model. A transfer function for each probe type was constructed from the model pressure history and the measured pressure history. The transfer function for each configuration accounts for damping and phase lag introduced by the probe configuration. Each of the probe configurations has distinct phase lag and damping and the transfer function for each will be dominated by different phenomena. The CTAP consists of a 0.0625 in (1.6 mm) diameter, 36 in (0.91 m) long tube connected to the RDE at one end and a pressure transducer at the other. In the tube, viscous dissipation results in a temporal average of the pressure. The dissipation results in strong damping of any perturbations. The length of the tube results in longer phase lag than any other configuration. In the ITP configuration, the pressure transducer is connected to the RDE by 1.5 in (3.8 cm) of 0.0625 in (1.6 mm) diameter tubing and to ambient air by 72 in (1.83 m) of 0.0625 in (1.6 mm) diameter tubing. The proximity of the transducer to the probe entrance reduces impact loading on the transducer and the open ended tube does not reflect Shockwaves. The distance from the tube entrance to the transducer results in little phase lag, but the small diameter tubing significantly damps pressure perturbations. The chamber connecting the transducer to the tubes resonates and the resonance of the chamber requires the transfer function be dependent on frequency. The direct Kiel probe was designed to minimize phase lag and damping of sinusoidal pressure oscillations; however, the Kiel probe seems to damp pressure oscillations more than the ITP. The Kiel probe is a shrouded, pitot stagnation pressure probe. The pitot tube has an internal diameter of 0.028 in (0.71 mm) and is 0.43 in (1.1 cm) long. The pressure transducer is connected to the tube by a small chamber. The small diameter of the pitot tube causes significant damping of pressure perturbations. The short length of the pitot tube results in short phase lag. In future investigation of RDEs the transfer functions developed for the CTAP, ITP, and Kiel probe configurations will prove useful calculating accurate pressure histories within the RDE and other, connected components.