Application of Particle Image Velocimetry to High-Speed Supersonic Flows in a Shock Tunnel
Particle Image Velocimetry (PIV) has become an important tool in modern flowfield diagnostics, in particular for subsonic flows. PIV systems have also been used to measure supersonic flows in supersonic wind tunnels, but only recently it has been shown that PIV can also be a valuable tool for high-speed supersonic flows in a shock tunnel (Haertig et al., 2001). At the ISL shock tunnel a PIV system was installed and tested (Fig. 1). A shock tunnel is a transient wind-tunnel facility with short testing times of a few milliseconds and high supersonic flow velocities in the km/s range. The short flow duration time makes a high information density highly desirable. An application of PIV to such kind of flows is considerably more difficult than to a continuous flows, however, because no online adjustments of the particle seeding and the optics can be done. In this publication, PIV measurement results obtained for flows at Mach numbers of 4.5 and 6 with velocities of up to 1.8 km/s are presented. We measured the freestream flow of nozzles, supersonic wedge flows with an attached shock wave, and the supersonic flow around a sphere with a detached shock wave. To obtain a good spatial resolution a laser pulse separation of less than 0.5 μs is necessary. Solid particles (TiO2 and Al2O3) with a nominal diameter of about 0.3 μm were used for the seeding. The measured particle relaxation across shock waves was found to be consistent with theoretical estimations. Because of the strong particle density gradients in shock waves, the PIV correlation algorithm can contribute to considerable inaccuracies, however. Fig. 1. ISL shock-tunnel facility with PIV system.
Flow visualization techniques in wind tunnels, Part I: Non optical methods
In this article, an attempt is made to describe and review the most widely used methods for flow visualization. The first part describes the basis and applications of different visualization methods (non optical) for subsonic and supersonic flow in wind and water tunnels: direct injection methods (smoke, dye, fog and different small particles) visualization methods by electrolytic and photochemical dye production, gas and hydrogen bubbles special techniques, flow visualization by tufts, oil, liquid crystals pressure and temperature sensitive paints. A considerable attention is paid to flow visualization techniques performed in VTI wind and water tunnels and almost all presented photos have been recorded during tests in laboratories of VTI. Optical methods and their application for compressible flow visualization will be given in the second part of the article.
A survey of particle image velocimetry applications in Langley aerospace facilities
This paper describes several applications of the global velocity measurement technique known as particle image velocimetry to three different facilities at Langley Research Center. These three applications represent global velocity measurements in distinctly different flows, namely a reacting hydrogen - air flame, a low Reynolds number boundary layer, and hypersonic flow over a wedge. In addition, these applications illustrate the power of the instrument to obtain data such as vorticity and Reynolds stress. Finally, the ability to obtain particle dynamics data in supersonic/hypersonic flows similar to that which can be obtained with point measurement techniques is demonstrated.