Accurate turbulence level estimations using PIV/PTV

Abstract

The estimation of the turbulence level of flow facilities is very important for the comprehensive description of experimental results. While for low flow velocities various measurement techniques can be used (for example hot-wire, LDV, PIV) the task becomes difficult in the case of compressible flows as temperature and density fluctuations bias the measurement of the velocity fluctuations. In this work, we analyze the free-stream flow of the trisonic wind tunnel Munich (TWM) by means of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The goal is to determine the flow quality, i.e. the turbulence level, over the operating range of the facility without bias due to temperature and density variations. The capability of PIV/PTV for the estimation of small velocity fluctuations is investigated in detail. It is shown that a small particle shift on the measurement plane in combination with a large particle image displacement on the image plane allows for precise velocity measurements. Furthermore, a variation of the time separation between the PIV double images, t , enables the measurement uncertainty to be determined, which was estimated to be as low as 0.04% of the mean displacement for a mean displacement of x = 100 pixel and an interrogation window size of 32 × 32 pixel. Regarding the wind tunnel turbulence, it was found that the turbulence level generally decreases with increasing Mach number for the TWM facility, starting with 1.9% at Ma = 0.3 and reaching 0.45% at Ma = 3.0 . With this analysis, a methodology exists to perform accurate turbulence measurements in incompressible and compressible flows.

Three-dimensional particle tracking velocimetry using shallow neural network for real-time analysis

“…where (! 6 , 2 6 ) is the location of a particle in (X, Y, Z) cartesian coordinates and the index i is for the number of the camera (here, i is 1 and 2). aij and bij are coefficients of each mapping function where j = 0, 1, 2, …, and 9.…”

“…Three-dimensional flow field measurement techniques have been developed for obtaining massive volumetric data sets for high temporal and spatial resolution from high-speed and multiple cameras while simultaneously reducing computation time and increasing reliability [1-3]. Among various three-dimensional flow field measurement techniques, it is known that particle tracking velocimetry (PTV) is able to obtain more complicated trajectories of particles and velocity vectors, for instance three-dimensional Reyleigh-Benard convection flow of the laminar-turbulent transition regime [4], three-dimensional vertical flow structures in a submerged hydraulic jump [5], and free-stream flow of the trisonic wind tunnel [6].…”

Investigation of the base flow of a generic space launcher with dual-bell nozzle

“…The free-stream turbulence level based on streamwise velocity fluctuations in the TWM test section is 1.9% at a Mach number of M = 0.3 and reduces with increasing Mach number reaching 0.45% at M = 3.0 . More details about the facility and its characterization are provided in [37,39].…”

Laboratory Study of Secondary Flow in an Open Channel Bend by Using PIV

“…Other instruments, e.g., velocity meter PROPLER [20] and P-EMS velocimeter [18], are unable to provide three components of a velocity vector. The popularization of PIV (Particle Image Velocimetry) in fluid mechanics shows promise as being a better instrumentation for measurement of curved flows [22][23][24][25][26]. In particular, some novel multi-pass window deformation approaches have been used to improve the performance of PIV in measurement of various flows [27][28][29].…”