The nano-particle-based planar laser scattering (NPLS) technique is used to measure the density distribution in the supersonic mixing layer of the convective Mach number 0.12, and the optical path difference (OPL)...The nano-particle-based planar laser scattering (NPLS) technique is used to measure the density distribution in the supersonic mixing layer of the convective Mach number 0.12, and the optical path difference (OPL), which is quite crucial for the study of aero-optics, is obtained by post processing. Based on the high spatiotemporal resolutions of the NPLS, the structure of the OPL is ana]ysed using wavelet methods. The coherent structures of the OPL are extracted using three methods, including the methods of thresholding the coefficients of the orthogonal wavelet transform and the wavelet packet transform, and preserving a number of wavelet packet coefficients with the largest amplitudes determined by the entropy dimension. Their performances are compared, and the method using the wavelet packet is the best. Based on the viewpoint of multifractals, we study the OPL by the wavelet transform maxima method (WTMM), and the result indicates that its scaling behaviour is evident.展开更多
The infrared imaging windows of the hyper/supersonic optical dome are encountering severe aero-optical effects[AOEs],so a flow control device,the ramp vortex generator array[RVGA]is proposed based on the ramp vortex g...The infrared imaging windows of the hyper/supersonic optical dome are encountering severe aero-optical effects[AOEs],so a flow control device,the ramp vortex generator array[RVGA]is proposed based on the ramp vortex generator to inhibit the supersonic mixing layers’AOE,which is done by the nanotracer-based planar laser scattering technique and ray-tracing method.The experiments prove that under different pressure conditions,RVGA can reduce the mean and standard deviation of the root mean square of the optical path difference[OPDrms]and reduce the supersonic mixing layers’thickness and mixture a great deal.The AOE of the pressure-matched mixing layer is the weakest.Higher RVGA results in better optical performance.RVGA has the potential to be applied to supersonic film cooling to reduce aero-optical aberrations.展开更多
Due to the difficulties in measuring supersonic density field, the multiresolution analysis of supersonic mixing layer based on experimental images is still a formidable challenge. By utilizing the recently developed ...Due to the difficulties in measuring supersonic density field, the multiresolution analysis of supersonic mixing layer based on experimental images is still a formidable challenge. By utilizing the recently developed nanoparticle based planar laser scattering method, the density field of a supersonic mixing layer was measured at high spatiotemporal resolution. According to the dynamic behavior of coherent structures, the multiresolution characteristics of density fluctuation signals and density field images were studied based on Taylor’s hypothesis of space-time conversion and wavelet analysis. The wavelet coefficients reflect the characteristics of density fluctuation signals at different scales, and the detailed coefficients reflect the differences of approximation at adjacent levels. The density fluctuation signals of supersonic mixing layer differ from the periodic sine signal and exhibit similarity to the fractal Koch signal. The similarity at different scales reveals the fractal characteristic of mixing layer flowfield. The two-dimensional wavelet decomposition and reconstruction of density field images extract the approximate and detailed signals at different scales, which effectively resolve the characteristic structures of the flowfield at different scales.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
The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on...The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized via NPLS,and the transient fine structures were identifiable in NPLS images,which were used to analyze the effects of flow control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer,delaying mixing layer transition; and the 3D tapes can enhance the 3D characteristic of the mixing layer,advancing mixing layer transition. 3D structures of the mixing layer were visualized,and the H-type Λ vortexes were found with 3D tapes control.展开更多
The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.Th...The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.The evolution of the combustion process in the supersonic reacting mixing layer is observed and unsteady phenomena of ignition,flame propagation and extinction are successfully captured.The ignition usually takes place at the air stream side of braid regions between two vortexes due to much higher temperature of premixed gases.After ignition,the flame propagates towards two vortexes respectively located on the upstream and downstream of the ignition position.The apparent flame speed is 1569.97 m/s,which is much higher than the laminar flame speed,resulting from the effects of expansion,turbulence,vortex stretching and consecutive ignition.After the flame arrives at the former vortex,the flame propagates along the outer region of the vortex in two branches.Then the upper flame branch close to fuel streamside distinguishes gradually due to too fuel-riched premixed mixtures in the front of the flame and the strong cooling effect of the adjacent cool fuel flow,while the lower flame branch continues to propagate in the vortex.展开更多
Numerical simulations have been performed for a 2D supersonic mixing layer with two different types of excitation, namely the introduction of a T-S wave at the inlet and the enforcement of the inflow speed on the low ...Numerical simulations have been performed for a 2D supersonic mixing layer with two different types of excitation, namely the introduction of a T-S wave at the inlet and the enforcement of the inflow speed on the low speed side to have periodic stream-wise undulations. The results showed that both ways were effective when the convective Mach number Mc was less than 1, but the latter was more effective than the former. Systematic computations have also been done to analyze the effect of different parameters on mixing.展开更多
The parameters of instability wave of supersonic mixing layer(Mc=0.5,M1=3.5/M2=1.4) are measured by flow visualization and calculated by means of two-dimensional direct numerical simulaitons of the compressible Navier...The parameters of instability wave of supersonic mixing layer(Mc=0.5,M1=3.5/M2=1.4) are measured by flow visualization and calculated by means of two-dimensional direct numerical simulaitons of the compressible Navier-Stokes equations.In both cases of the mixing layer with harmonic disturbance or not,the comparative results indicate that the wavelength of the two-dimensional wave is equal to the vortex spacing in the streamwise direction because the difference between them is less than 1%.However,the measured convective velocity of the large-scale structure deviates from the theoretical isentropic prediction about 10%.Here the measured value confirms that Mc,2<Mc,1 for the supersonic-supersonic mixing layer.Furthermore,the pairing and intermittent phenomenon are recorded clearly by flow visualization.展开更多
The density field measurement of supersonic mixing layer based on the nanoparticle-based planar laser scattering method was studied.The calibration of experimental images was analyzed,and the relation between tracer p...The density field measurement of supersonic mixing layer based on the nanoparticle-based planar laser scattering method was studied.The calibration of experimental images was analyzed,and the relation between tracer particles concentration and local density of flowfield was calibrated with oblique shockwave experiment.According to the characteristic of mixing layer images,the influence of uneven light intensity distribution was calibrated.With these calibration methods,the density field of supersonic mixing layer with convective Mach number at 0.12 was measured.By analyzing the spanwise vortical structures and streamwise density field,the three dimensional(3D) density field was approximately reconstructed,which apparently reflected the 3D structure of supersonic mixing layer.展开更多
The spatial evolution of a T-S wave and its subharmonic wave, introduced at the inlet in a 2-D supersonic mixing layer, was investigated by using DNS. The relationship between the amplitude of the disturbance wave and...The spatial evolution of a T-S wave and its subharmonic wave, introduced at the inlet in a 2-D supersonic mixing layer, was investigated by using DNS. The relationship between the amplitude of the disturbance wave and the strength of the shocklet caused by the disturbance was investigated. We analyzed the shape of the disturbance velocity profile on both sides of the shocklet, and found that the existence of shocklet affected appreciably the disturbance velocity. The effects on the high speed side and low speed side of the mixing layer were found to be different.展开更多
The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow paramete...The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.展开更多
A sonic under-expanded transverse jet injection into a Ma 1.6 supersonic crossflow is investigated numerically using our hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) method. First, a calcula...A sonic under-expanded transverse jet injection into a Ma 1.6 supersonic crossflow is investigated numerically using our hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) method. First, a calculation is carried out to validate the code, where both the instantaneous and statistical results show good agreement with the existing experimental data. Then the jet-mixing characteristics are analyzed. It is observed that the large-scale vortex on the windward portion of the jet boundary is formed mainly by the intermittent impingement of the incoming high-speed fluid on the relatively low-speed region of the upstream jet boundary, where the interaction between the upstream separated region and the jet supplies a favorable pressure condition for the sustaining acceleration of the high-speed fluid during the vortex forming, associated with which the incoming fluid is entrained into the jet boundary and large-scale mixing occurs. Meanwhile, the secondary recirculation zone between the upstream separated region and the jet is observed to develop evidently during the vortex forming, inducing the entrainment of jet fluid into the upstream separated region. Moreover, effects of the incoming boundary layer on the jet mixing are addressed.展开更多
基金Projected supported by the Innovation Research Foundations for Postgraduates of National University of Defense Technology and Hunan Provincethe National Natural Science Foundation of China (Grant No. 61008037)
文摘The nano-particle-based planar laser scattering (NPLS) technique is used to measure the density distribution in the supersonic mixing layer of the convective Mach number 0.12, and the optical path difference (OPL), which is quite crucial for the study of aero-optics, is obtained by post processing. Based on the high spatiotemporal resolutions of the NPLS, the structure of the OPL is ana]ysed using wavelet methods. The coherent structures of the OPL are extracted using three methods, including the methods of thresholding the coefficients of the orthogonal wavelet transform and the wavelet packet transform, and preserving a number of wavelet packet coefficients with the largest amplitudes determined by the entropy dimension. Their performances are compared, and the method using the wavelet packet is the best. Based on the viewpoint of multifractals, we study the OPL by the wavelet transform maxima method (WTMM), and the result indicates that its scaling behaviour is evident.
基金supported by the National Natural Science Foundation of China(No.12102463)the National Defense Basic Scientific Research Program of China(No.2022-JCJQJJ-1123)the Natural Science Foundation of Hunan Province(No.2021JJ40652)。
文摘The infrared imaging windows of the hyper/supersonic optical dome are encountering severe aero-optical effects[AOEs],so a flow control device,the ramp vortex generator array[RVGA]is proposed based on the ramp vortex generator to inhibit the supersonic mixing layers’AOE,which is done by the nanotracer-based planar laser scattering technique and ray-tracing method.The experiments prove that under different pressure conditions,RVGA can reduce the mean and standard deviation of the root mean square of the optical path difference[OPDrms]and reduce the supersonic mixing layers’thickness and mixture a great deal.The AOE of the pressure-matched mixing layer is the weakest.Higher RVGA results in better optical performance.RVGA has the potential to be applied to supersonic film cooling to reduce aero-optical aberrations.
基金supported by the National Natural Science Fumdation of China (Grant No. 10672178)
文摘Due to the difficulties in measuring supersonic density field, the multiresolution analysis of supersonic mixing layer based on experimental images is still a formidable challenge. By utilizing the recently developed nanoparticle based planar laser scattering method, the density field of a supersonic mixing layer was measured at high spatiotemporal resolution. According to the dynamic behavior of coherent structures, the multiresolution characteristics of density fluctuation signals and density field images were studied based on Taylor’s hypothesis of space-time conversion and wavelet analysis. The wavelet coefficients reflect the characteristics of density fluctuation signals at different scales, and the detailed coefficients reflect the differences of approximation at adjacent levels. The density fluctuation signals of supersonic mixing layer differ from the periodic sine signal and exhibit similarity to the fractal Koch signal. The similarity at different scales reveals the fractal characteristic of mixing layer flowfield. The two-dimensional wavelet decomposition and reconstruction of density field images extract the approximate and detailed signals at different scales, which effectively resolve the characteristic structures of the flowfield at different scales.
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The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized via NPLS,and the transient fine structures were identifiable in NPLS images,which were used to analyze the effects of flow control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer,delaying mixing layer transition; and the 3D tapes can enhance the 3D characteristic of the mixing layer,advancing mixing layer transition. 3D structures of the mixing layer were visualized,and the H-type Λ vortexes were found with 3D tapes control.
文摘The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.The evolution of the combustion process in the supersonic reacting mixing layer is observed and unsteady phenomena of ignition,flame propagation and extinction are successfully captured.The ignition usually takes place at the air stream side of braid regions between two vortexes due to much higher temperature of premixed gases.After ignition,the flame propagates towards two vortexes respectively located on the upstream and downstream of the ignition position.The apparent flame speed is 1569.97 m/s,which is much higher than the laminar flame speed,resulting from the effects of expansion,turbulence,vortex stretching and consecutive ignition.After the flame arrives at the former vortex,the flame propagates along the outer region of the vortex in two branches.Then the upper flame branch close to fuel streamside distinguishes gradually due to too fuel-riched premixed mixtures in the front of the flame and the strong cooling effect of the adjacent cool fuel flow,while the lower flame branch continues to propagate in the vortex.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 19732005) and the National Climbing Project.
文摘Numerical simulations have been performed for a 2D supersonic mixing layer with two different types of excitation, namely the introduction of a T-S wave at the inlet and the enforcement of the inflow speed on the low speed side to have periodic stream-wise undulations. The results showed that both ways were effective when the convective Mach number Mc was less than 1, but the latter was more effective than the former. Systematic computations have also been done to analyze the effect of different parameters on mixing.
基金Supported by the National Natural Science Foundation of China (Grant No.10772168)
文摘The parameters of instability wave of supersonic mixing layer(Mc=0.5,M1=3.5/M2=1.4) are measured by flow visualization and calculated by means of two-dimensional direct numerical simulaitons of the compressible Navier-Stokes equations.In both cases of the mixing layer with harmonic disturbance or not,the comparative results indicate that the wavelength of the two-dimensional wave is equal to the vortex spacing in the streamwise direction because the difference between them is less than 1%.However,the measured convective velocity of the large-scale structure deviates from the theoretical isentropic prediction about 10%.Here the measured value confirms that Mc,2<Mc,1 for the supersonic-supersonic mixing layer.Furthermore,the pairing and intermittent phenomenon are recorded clearly by flow visualization.
基金supported by the National Natural Science Foundation of China (10672178)
文摘The density field measurement of supersonic mixing layer based on the nanoparticle-based planar laser scattering method was studied.The calibration of experimental images was analyzed,and the relation between tracer particles concentration and local density of flowfield was calibrated with oblique shockwave experiment.According to the characteristic of mixing layer images,the influence of uneven light intensity distribution was calibrated.With these calibration methods,the density field of supersonic mixing layer with convective Mach number at 0.12 was measured.By analyzing the spanwise vortical structures and streamwise density field,the three dimensional(3D) density field was approximately reconstructed,which apparently reflected the 3D structure of supersonic mixing layer.
基金the National Natural Science Foundation of China (Grant No. 19732005) the National Climbing Project of China.
文摘The spatial evolution of a T-S wave and its subharmonic wave, introduced at the inlet in a 2-D supersonic mixing layer, was investigated by using DNS. The relationship between the amplitude of the disturbance wave and the strength of the shocklet caused by the disturbance was investigated. We analyzed the shape of the disturbance velocity profile on both sides of the shocklet, and found that the existence of shocklet affected appreciably the disturbance velocity. The effects on the high speed side and low speed side of the mixing layer were found to be different.
文摘The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50906098 and 91016028)Fok Ying Tung Education Foundation (Grant No. 131055)
文摘A sonic under-expanded transverse jet injection into a Ma 1.6 supersonic crossflow is investigated numerically using our hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) method. First, a calculation is carried out to validate the code, where both the instantaneous and statistical results show good agreement with the existing experimental data. Then the jet-mixing characteristics are analyzed. It is observed that the large-scale vortex on the windward portion of the jet boundary is formed mainly by the intermittent impingement of the incoming high-speed fluid on the relatively low-speed region of the upstream jet boundary, where the interaction between the upstream separated region and the jet supplies a favorable pressure condition for the sustaining acceleration of the high-speed fluid during the vortex forming, associated with which the incoming fluid is entrained into the jet boundary and large-scale mixing occurs. Meanwhile, the secondary recirculation zone between the upstream separated region and the jet is observed to develop evidently during the vortex forming, inducing the entrainment of jet fluid into the upstream separated region. Moreover, effects of the incoming boundary layer on the jet mixing are addressed.