Estimation of the rate of turbulent liquid flow in the pipeline based on surface measurements of flow noise

The article presents the results of numerical and experimental studies, which are aimed at improving the accuracy of non-intrusive measurements of the temperature of a liquid flow in pipelines, which are elements of hydraulic systems of machines and mechanisms. The auxiliary problem of estimating the fluid flow rate by measuring the intensity of noise on the surface of the pipeline is being solved. The noise source in the pipeline is the fluid velocity fluctuations in the turbulent flow, which we perceive as pressure and sound fluctuations, while for high flow velocities the distribution of the average velocity in the pipe cross section is quite uniform and has a logarithmic character, and the total flow temperature is close to the center of the pipe. However, at low and moderate flow rates, the temperature distribution is uneven and the error from the un-evenness can make a significant contribution to the overall measurement error, especially with measurement using relatively accurate resistance thermometers. Therefore, it is necessary to introduce a correction function of the average flow rate and compensate the measurement error due to not-enough flow uniformity, to increase the accuracy of non-intrusive temperature measurements. A reasonable choice is made of a numerical simulation environment suitable for the requirements of this problem: the turbulence energy density in a pipeline with two bends (temperature compensator), the turbulence energy dissipation, the distribution of turbulence energy in the flow cross section at one of the bends were calculated. This allows us to say that the maximum values of the energy density of turbulence arise on the side walls of the pipeline bend in the boundary layer of the flow, and the dependence of energy on speed is described by a polynomial of the third degree, that is consistent with the results of other authors. In addition, the insertion of a logarithmic scale for the dependence of turbulence energy on speed allows to linearize this dependence and, thus, construct a linear measurement function for the moderate and large Reynolds numbers range. An experimental study was conducted on a flowstand in a flow range of up to 0.1 kg/s with DN50 pipeline and temperatures of 20 and 80 °С. The spectral characteristics of the signals on the pipeline surface were determined. Was revealed that for surface noise, as well as for noise in the center of the pipeline, there are three characteristic spectral zones are characteristic, and the first zone (energy-bearing) is informational and should be the object of measurements. The width of this zone is proportional to the flow rate and can be determined by frequency detection methods. A quadratic amplitude detector can be used to determine the energy intensity of the noise signal in the energy-carrying band of the spectrum.