Non-intrusive acoustic measurement of flow velocity and temperature in a high subsonic Mach number jet

Abstract

In previous studies, sonic anemometry and thermometry have generally been used to measure low subsonic Mach flow conditions. Recently, a novel configuration was proposed and used to measure unheated jet velocities up to Mach 0.83 non-intrusively. The objective of this investigation is to test the novel configuration in higher temperature conditions and explore the effects of fluid temperature on mean velocity and temperature measurement accuracy. The current work presents non-intrusive acoustic measurements of single-stream jet conditions up to Mach 0.7 and total temperatures from 299 K to 700 K. Comparison of acoustically measured velocity and static temperature with probe data indicate root mean square (RMS) velocity errors of 2.6 m s−1 (1.1% of the maximum jet centerline velocity), 4.0 m s−1 (1.2%), and 8.5 m s−1 (2.4%), respectively, for 299, 589, and 700 K total temperature flows up to Mach 0.7. RMS static temperature errors of 7.5 K (2.5% of total temperature), 8.1 K (1.3%), and 23.3 K (3.3%) were observed for the same respective total temperature conditions. To the authors’ knowledge, this is the first time a non-intrusive acoustic technique has been used to simultaneously measure mean fluid velocity and static temperatures in high subsonic Mach numbers up to 0.7. Overall, the findings of this work support the use of acoustics for non-intrusive flow monitoring. The ability to measure mean flow conditions at high subsonic Mach numbers and temperatures makes this technique a viable candidate for gas turbine applications, in particular.

In-flight thrust monitoring: an acoustics-based approach

“…The time of flight in equation (1) is sensitive to both temperature (via the thermodynamic sound speed) and the flow velocity along the ray path. To measure these flow variables, the concepts described by Otero et al for jet experiments (Otero et al , 2017a, 2017b) may be used to obtain the path-integrated flow velocity and speed of sound. The procedure for obtaining path-integrated temperatures and velocities is outlined in Appendix A of Otero et al ’s (2017a) work.…”

“…For special cases, such as a uniform flow field, unique relationships may be derived for temperature and velocity based upon the relative placement of the acoustic transmitter, two receivers and measured times of flight. For more general cases, iterative ray tracing is necessary, but measurements remain tractable (Otero et al , 2017b).…”

“…In the past works, a number of uncertainty drivers have been identified, quantified and mitigated where possible (Otero et al , 2017a, 2017b, 2018). These include signal-to-noise ratio, positioning uncertainty for sensors and acoustic path reconstruction errors.…”

“…These include signal-to-noise ratio, positioning uncertainty for sensors and acoustic path reconstruction errors. Laboratory demonstrations of the technique yielded root-mean-square (RMS) static temperature errors of 1-3 per cent and RMS velocity errors of 1-2.5 per cent (Otero et al , 2017b) over a wide range of free jet total temperatures (up to 700 K) and Mach number (up to 0.83). The laboratory successes led the authors to pursue a ground test application in the research engine at Virginia Tech to use simplified, two-path acoustic measurements for inferring engine thrust.…”

“…A non-intrusive acoustic method, as outlined by Otero et al (2017a, 2017b), is discussed for future in-flight measurement of engine exhaust properties. The proposed acoustic technique relies on the fundamentals of sonic anemometry and thermometry, which have been around for many years (Cuerva and Sanz-Andrés, 2000; Cuerva et al , 2003; Banfield and Dissly, 2005; Wyngaard, 1981; Sozzi and Favaron, 1996; McKeon et al , 2007; Kaimal and Gaynor, 1991), but uses a new configuration to estimate higher subsonic Mach number flow characteristics simultaneously.…”