The existing methods for measuring aero-optical aberration suffer from several problems,such as low spatiotemporal resolution,sensitivity to environment,and integral effects.A new method for measuring aero-optical abe...The existing methods for measuring aero-optical aberration suffer from several problems,such as low spatiotemporal resolution,sensitivity to environment,and integral effects.A new method for measuring aero-optical aberration of supersonic flow is proposed.Based on the self-developed measuring method of supersonic density field,the wavefront aberration induced by a cross-section of supersonic flow field could be measured by ray-tracing.Compared with other methods,the present one has three significant innovations:(1) high spatiotemporal resolution.Its time resolution is 6 ns,and the spatial resolution can reach up to micrometers;(2) it can avoid the integral effects and study the wavefront aberration induced by the flow field of interest locally;(3) it can also avoid the influence from the test section wall boundary layers and environmental disturbances.The present method was applied to supersonic flow around an optical bow cap.The results of high spatiotemporal resolution reveal fine wavefront structures,and show that shock waves,expansion waves and turbulent boundary layers have different impacts on the wavefront aberration.展开更多
The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in rele...The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in relevant studies. A high resolution whole-field aero-optical aberration and dithering measuring method based on the Background Orient Schlieren (BOS) technique was studied. The systematic structure, sensitivity and resolution of BOS are analyzed in this paper. The aero-optical aberration and dithering of streamwise structures in supersonic mixing layers were quantificationally studied with BOS. The aberration field of spanwise structures revealed the ribbon-like aberration structures, which heavily restrict the optical performance of a mixing layer. The quantifications of aero-optical aberration and dithering are very important in studying aero-optical performance of supersonic mixing layer.展开更多
A collimated light beam will be refracted if it propagates through a flow-field with index-of-refraction variations,and its wavefront will be distorted.If we measure the deflection angle of the light beam,the gradient...A collimated light beam will be refracted if it propagates through a flow-field with index-of-refraction variations,and its wavefront will be distorted.If we measure the deflection angle of the light beam,the gradient of the wavefront can be obtained using the Malus law,and the wavefront aberration can be computed with a reconstruction algorithm.Two characteristics of background oriented schlieren(BOS) are conducive to wavefront aberration measurement:BOS can be used to measure the deflection angle of a light beam by measuring the displacement field between the reference image and the experiment image.Moreover,in a BOS system of Schlieren mode,only the ray perpendicular to the background image can be captured with a camera.This is helpful to measure wavefront aberrations that occur after a planar wavefront has passed through the flow-field.Based on these characteristics of BOS of Schlieren mode,a new wavefront measurement technique,which is called the BOS-based wavefront technique(BOS-WT),is proposed in this paper.It works by constructing the relationship between the displacement of the background image and the aero-optical wavefront gradient and uses the Southwell wavefront reconstruction algorithm.A BOS-WT system was assembled,and its temporal resolution was found to be 6 ns,and its temporal-correlation resolution reached 0.2 μs.A BOS-WT can measure the time-correlation transient wavefront quantitatively.It is simple and easy to operate.In this paper,we also present a study of the aero-optical performance of supersonic mixing layer based on our BOS-WT transient wavefronts at an interval of 5 μs.The results showed the wavefront was transient and distorted after it had passed through the mixing layer.Through the analysis of the data at the 5 μs interval,the temporal evolution of wavefront can be obtained.展开更多
基金supported by the National Natural Science Foundation of China (10672178, 10772168)National Basic Research Program of China (2009CB724100)
文摘The existing methods for measuring aero-optical aberration suffer from several problems,such as low spatiotemporal resolution,sensitivity to environment,and integral effects.A new method for measuring aero-optical aberration of supersonic flow is proposed.Based on the self-developed measuring method of supersonic density field,the wavefront aberration induced by a cross-section of supersonic flow field could be measured by ray-tracing.Compared with other methods,the present one has three significant innovations:(1) high spatiotemporal resolution.Its time resolution is 6 ns,and the spatial resolution can reach up to micrometers;(2) it can avoid the integral effects and study the wavefront aberration induced by the flow field of interest locally;(3) it can also avoid the influence from the test section wall boundary layers and environmental disturbances.The present method was applied to supersonic flow around an optical bow cap.The results of high spatiotemporal resolution reveal fine wavefront structures,and show that shock waves,expansion waves and turbulent boundary layers have different impacts on the wavefront aberration.
基金Supported by the National Natural Science Foundation of China (Grant No.10672178)
文摘The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in relevant studies. A high resolution whole-field aero-optical aberration and dithering measuring method based on the Background Orient Schlieren (BOS) technique was studied. The systematic structure, sensitivity and resolution of BOS are analyzed in this paper. The aero-optical aberration and dithering of streamwise structures in supersonic mixing layers were quantificationally studied with BOS. The aberration field of spanwise structures revealed the ribbon-like aberration structures, which heavily restrict the optical performance of a mixing layer. The quantifications of aero-optical aberration and dithering are very important in studying aero-optical performance of supersonic mixing layer.
文摘A collimated light beam will be refracted if it propagates through a flow-field with index-of-refraction variations,and its wavefront will be distorted.If we measure the deflection angle of the light beam,the gradient of the wavefront can be obtained using the Malus law,and the wavefront aberration can be computed with a reconstruction algorithm.Two characteristics of background oriented schlieren(BOS) are conducive to wavefront aberration measurement:BOS can be used to measure the deflection angle of a light beam by measuring the displacement field between the reference image and the experiment image.Moreover,in a BOS system of Schlieren mode,only the ray perpendicular to the background image can be captured with a camera.This is helpful to measure wavefront aberrations that occur after a planar wavefront has passed through the flow-field.Based on these characteristics of BOS of Schlieren mode,a new wavefront measurement technique,which is called the BOS-based wavefront technique(BOS-WT),is proposed in this paper.It works by constructing the relationship between the displacement of the background image and the aero-optical wavefront gradient and uses the Southwell wavefront reconstruction algorithm.A BOS-WT system was assembled,and its temporal resolution was found to be 6 ns,and its temporal-correlation resolution reached 0.2 μs.A BOS-WT can measure the time-correlation transient wavefront quantitatively.It is simple and easy to operate.In this paper,we also present a study of the aero-optical performance of supersonic mixing layer based on our BOS-WT transient wavefronts at an interval of 5 μs.The results showed the wavefront was transient and distorted after it had passed through the mixing layer.Through the analysis of the data at the 5 μs interval,the temporal evolution of wavefront can be obtained.
