Nano-tracer Planar Laser Scattering Research Articles

Application of Nano Technique in Measuring Supersonic/Hypersonic Flow

Turbulence, universally exist in nature and human activities, is a kind of three-dimensional, irregular, unsteady flow. Ever since 19th century when people started to investigated turbulent flow technically, they have never dropped the po-tent and intuitionistic experimental method. Recently, with the development of aviation and aerospace industry， espe-cially with the increase desire of supersonic and hypersonic flight, the mechanism of high speed and compressible flow has become hot topic of fluid research, resulting in development of measurement method and technique. When encoun-tering compressible high flow, traditional techniques, such as schilieren, shadow and interference, cannot measure fine flow structures. Fortunately, multiple-discipline integration of nano technique, laser technique and imaging technique provides a new design for fluid measurement。Nano-tracer planar laser scattering (NPLS) is a new flow visualization technique, which was developed by the authors’ group in 2005, and it can visualize time correctional flow structure in a cross-section of instantaneous 3D supersonic flow at high spatiotemporal resolution. Many studies have demonstrated that NPLS is a powerful tool to study supersonic turbulence.

Experimental investigation on aero-optical aberration of the supersonic flow passing through an optical dome with gas injection

During the flight in the atmosphere, the optical window of an optical dome needs to be cooled, and supersonic film cooling is one of the economic ways. After traversing through the complex flow field above the window, the optical wave would be distorted by fluctuations in the density field due to the expansion wave, shockwave, mixing layer, turbulent boundary layer, etc. The aero-optical aberrations induced by the flow field of an optical dome in the presence and in the absence of the gas injection at Mach 3.8 are investigated experimentally. Based on the nano-tracer planar laser scattering (NPLS) technique, the density field with high spatial-temporal resolution is first obtained by the flow image calibration, and then the optical path difference (OPD)fluctuations of the original 532 nm planar wavefront perpendicular to the window are calculated using Ray-tracing theory. Also the OPD fluctuations caused by the near-wall region flow structures are presented. In the absence of the gas injection, the flow structure is relatively simple with a long recirculation and laminar region, while in the presence of the gas injection, there appear more complex structures such as shear layer, mixing layer and turbulent boundary layer and the flow is converted into turbulence quickly. Clearly, the optical aberration in the presence of the gas injection is degraded more. For example, the values of root-mean-square OPD (OPDrms) in the absence of the gas injection are 0.038 μm and 0.0356 μm, and they are 0.0462 μm, and 0.0485 μm in the presence of the gas injection during the interval 5 μs.

THE NEW ADVANCE OF THE EXPERIMENTAL RESEARCH ON COMPRESSIBLE TURBULENCE BASED ON THE NPLS TECHNIQUE

The experimental research on the mechanics of compressible turbulence has long been a serious challenge.Major difficulties exist in the development of non-intrusive techniques for measuring fine structures with high spatiotemporal resolution and the technique of low-noise high-speed wind tunnel design.With the aid of the newly developed nano-tracer planar laser scattering (NPLS) technique and the successful design of the low-noise-level supersonic/hypersonic wind tunnel,the experimental researches on compressible turbulence advanced rapidly.Recent progresses achieved by our research group in the study of non-intrusive techniques such as NPLS,background oriented schlieren (BOS) and particle image velocimetry (PIV),and their applications in measuring fine structures in high-speed flows are reported in this paper.,including the transition of supersonic mixing layer and boundary layer,the supersonic flow field around a body and their wake flow,the interaction between shock wave and turbulent boundary layer.The studies of the aero-optics in above flow fields are also introduced.The future prospects of the experimental research on the mechanics of compressible turbulence are also discussed here.At the end of paper,the research on turbulence mechanism,which is now under way,and its potential contributions to engineering modeling of turbulence are also elucidated.