Experimental Investigation of Cavitation Induced Feedline Instability from an Orifice

Abstract

T his paper details the results of an experimental investigation into the cavitation instabilities created by a circular orifice conducted at the University of A labama in H untsville Propulsion Resea rch C enter. T his experiment was conducted in concert with a computational simulation to serve as a reference point for the simulation. T esting was conducted using liquid nitrogen as a cryogenic propellant simulant. A 1.06 cm diameter thin orifice with a rounded inlet was tested in an approximately 1.25 kg/s flow with inlet pressures ranging from 504.1 kPa to 829.3 kPa. Pressure fluctuations generated by the orifice were measured using a high frequency pressure sensor located 0.64 tube diameters downstream of the orifice. F ast Fourier T ransforms were performed on the high frequency data to determine the instability frequency. Shedding resulted in a primary frequency with a cavitation related subharmonic frequency. For this experiment, the cavitation instability ranged from 153 H z to 275 H z. A dditionally, the strength of the cavitation occur red as a function of cavitation number. A t lower cavitation numbers, the strength of the cavitation instability ranged from 2.4 % to 7 % of the inlet pressure. However, at higher cavitation numbers, the strength of the cavitation instability ranged from 0.6 % to 1 % of the inlet pressure.

Monitoring Cavitation Regime From Pressure and Optical Sensors: Comparing Methods Using Wavelet Decomposition for Signal Processing

“…Statistical analysis based on Fast Fourier transform (FFT) and on wavelet transform was widely used in signal processing showing good performances for analysis of these signals. Fast Fourier Transforms were performed on the high frequency data acquired by pressure sensors to determine the instability frequency related to the development of cryogenic cavitation in an orifice [9]. In [10] the power spectral density (PSD), and the probability density function (PDF) of the void-fraction signal from a capacitance sensors were used to objectively identify the flow pattern in two phase flows.…”

High-Speed Flame Radiation Imaging of Thermoacoustic Coupling in a High Pressure Research Thrust Chamber

“…12. For this load point dominant peaks are present which match to the 1L mode frequency range, but most importantly the frequency of the 1L mode of the post yields in this case Strouhal numbers around 0.35, which is in the range where acoustic excitation due to orifice whistling phenomena have been described in literature [30][31][32]. Therefore it is possible that hydrodynamic effects as periodic vortex shedding at the LOX post throttle orifice excites the LOX posts or at least may amplify the acoustic oscillations in the LOX post.…”

“…Typical Strouhal number values for orifice flow hydrodynamics exciting the tube acoustic eigenmodes are in the range 0.2-0.35 [30]. Hitt et al found a maximum response for the flow of cryogenic nitrogen through a thin orifice at a Strouhal number of 0.28 ± 10 % [31]. The investigation of Lacombe et al [32] came to the result that acoustic amplification due to orifice whistling can be observed in the range 0.2 to 0.4.…”

Cavitation Regime Detection by LS-SVM and ANN With Wavelet Decomposition Based on Pressure Sensor Signals

“…Statistical analysis based on Fast Fourier transform (FFT) and on wavelet transform was widely used in signal processing showing good performances for analysis of these signals. In [10] Fast Fourier Transforms was applied to the pressure fluctuations generated in the orifice in presence of cryogenic cavitation to investigate the related instability frequency.…”