Measurement of active grid generated turbulence

• Published in: Proceedings in applied mathematics and mechanics Vol. 24; no. 4
• Main Authors: Faragó, Dávid, Szaszák, Norbert, Bencs, Péter
• Format: Journal Article
• Language: English
• Published: 01.12.2024
• ISSN: 1617-7061; 1617-7061
• DOI: 10.1002/pamm.202400167

The aim of the research is to investigate the flow field downstream of an active turbulence grid using LDA (laser Doppler anemometry) and CTA (constant temperature anemometry) measurement methods. The work includes the development of measurement cases, the designing and realization of the measurement and auxiliary systems. The investigation has been realized in an open, Göttingen‐type wind tunnel, with a measurement cross‐section of 0.6 ×$\times$ 0.5 m. The investigated grid type, active turbulence generator was placed downstream of the converging nozzle section of the wind tunnel. Flexible silicone tubes were attached to certain grid points of the turbulence generator. Based on preliminary experiment results, silicone tubes were placed at every second grid point in a checkerboard pattern, and the remaining grid point openings were sealed. In active and in jet modes of the grid, it was supplied with high pressure secondary air (up to 8 bar gauge pressure). The appropriate volume flow rate was set by adjusting a pressure reducer and a variable cross‐section volume flow meter. The flow downstream of the turbulence grid was examined at five different mean air velocities with the turbulence generator being operated in passive, jet, and active modes. Reynolds numbers and the ratios of secondary volume flow to primary volume flow were determined from other measured (velocities, temperatures, pressure values, relative air humidity) and derived (densities, volume‐ and mass flow rates) quantities. Using LDA, the streamwise and the vertical velocity components (u$u$‐w$w$) were measured. Using CTA, measurements were performed twice; once measuring the streamwise and the horizontal instantaneous velocity components (u$u$‐v$v$), and the second time measuring the streamwise and the vertical components (u$u$‐w$w$). The results were processed and visualized in Matlab.