The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed i...The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.展开更多
The paper evaluates the evolvement of coherent structures and penetration height of gaseous transverse jet penetration into a supersonic turbulent flow.The high spatiotemporal resolution coherent structures of the jet...The paper evaluates the evolvement of coherent structures and penetration height of gaseous transverse jet penetration into a supersonic turbulent flow.The high spatiotemporal resolution coherent structures of the jet plume are obtained by utilizing the nanoparticle-based planar laser scattering technique(NPLS).The evolving pattern of the coherent structures generated on the upwind surface of the transverse jet is analyzed based on the NPLS images.The shedding eddies from the jet near-field have lower convection velocity along freestream direction,while vortex growth rate is apparently higher than the far-field.Farther downstream,the large-scale eddies have less deformation and translate at velocities near the freestream velocity.Thus the near-field determines the scale of eddies in the far-field and affects the whole mixing process.The effect of injection stagnation pressure on the coherent structures is discussed and a modified penetration correlation is proposed based on an edge approximation definition and least square method with various injection pressures.展开更多
Experimental results from a series of injection tests of pressurized H2, N2 gases into Mach 1.8 airfiows between parallel channel walls through a flush-mounted circular sonic opening have been presented.Schlieren pict...Experimental results from a series of injection tests of pressurized H2, N2 gases into Mach 1.8 airfiows between parallel channel walls through a flush-mounted circular sonic opening have been presented.Schlieren pictures revealed complex interaction flow features including the occurrence of bow/separation shock waves due to the injection as well as the barrel shock/Mach disc structure inside the injected gas stream. The injectant penetration measured by the Mach disc height against the injection pressure showed a good agreement with the correlation curve based upon the "effective back pressure" concept. The reversed flow region beneath the separation shock wave, the injectant wake and its associated flow entraimment were also visualized by the oil paint method. Wall static pressure distributions around the injector were measured in detail, which corresponded very well to the above results of flow visualization.Gas samplings were also undertaken by using the pressure taps to confirm the presence of H2 gas in the separation region ahead of the injector. Traversing of total pressure and H2 gas concentration at the exit of the test channel showed monotonous increase of the loss while its profile was kept very similar with the injection pressure. The area indicating the loss and the presence of H2 gas almost coincided with each other, which remained to be small to indicate very slow gas mixing/diffusion with the main air flow. With the increase of airflow total temperature to 1200 K, a bulk flame was first observed at the exit section. Further increase up to 1460 K observed an ignition flame at the injector. However,the reflection of the bow shock wave was found to be a more likely trigger of the bulk flame ignition within the test section.展开更多
Hydrogen gas has been injected transversely into Mach 1.8 airflow between parallel channel walls from two circular sonic injectors which were mounted flush and placed in tandem along the centre line of the bottom wall...Hydrogen gas has been injected transversely into Mach 1.8 airflow between parallel channel walls from two circular sonic injectors which were mounted flush and placed in tandem along the centre line of the bottom wall plate of a test section. Both cold and hot airnow conditions, i.e. atmospheric and heated to max.1460K total temperature, were tested. In the cold flow experiments, detailed measurements were successful and the tandem injection resulted in a marked difference from the single injection with respect to the pattern of shock waves and the distribution of pressure and hydrogen concentration near the injector region. Upon changing the injection pressure ratio between the two injectors, it has been revealed that a prior injection upstream of the main injection would be beneficial in terms of the total pressure loss in the airflow and the hydrogen concentration near the injector region while maintaining the mixing performance. In general, the flow features showed little difference as the airflow temperature was raised until hydrogen burning was observed, whence the results became inevitably less quantitative. Against the expectation from the cold flow tests, a prior injection of cold hydrogen has resulted in quenching the main injector flame.展开更多
基金supported by the Science Foundation of National University of Defense Technology (No. JC11-01-02)the Hunan Provincial Natural Science Foundation of China (No.12jj4047)
文摘The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91116001,91016028 and 91216303)Fok Ying Tung Education Foundation (Grant No. 131055)a fund for owner of outstanding doctorial dissertation from the Education Ministry of China
文摘The paper evaluates the evolvement of coherent structures and penetration height of gaseous transverse jet penetration into a supersonic turbulent flow.The high spatiotemporal resolution coherent structures of the jet plume are obtained by utilizing the nanoparticle-based planar laser scattering technique(NPLS).The evolving pattern of the coherent structures generated on the upwind surface of the transverse jet is analyzed based on the NPLS images.The shedding eddies from the jet near-field have lower convection velocity along freestream direction,while vortex growth rate is apparently higher than the far-field.Farther downstream,the large-scale eddies have less deformation and translate at velocities near the freestream velocity.Thus the near-field determines the scale of eddies in the far-field and affects the whole mixing process.The effect of injection stagnation pressure on the coherent structures is discussed and a modified penetration correlation is proposed based on an edge approximation definition and least square method with various injection pressures.
文摘Experimental results from a series of injection tests of pressurized H2, N2 gases into Mach 1.8 airfiows between parallel channel walls through a flush-mounted circular sonic opening have been presented.Schlieren pictures revealed complex interaction flow features including the occurrence of bow/separation shock waves due to the injection as well as the barrel shock/Mach disc structure inside the injected gas stream. The injectant penetration measured by the Mach disc height against the injection pressure showed a good agreement with the correlation curve based upon the "effective back pressure" concept. The reversed flow region beneath the separation shock wave, the injectant wake and its associated flow entraimment were also visualized by the oil paint method. Wall static pressure distributions around the injector were measured in detail, which corresponded very well to the above results of flow visualization.Gas samplings were also undertaken by using the pressure taps to confirm the presence of H2 gas in the separation region ahead of the injector. Traversing of total pressure and H2 gas concentration at the exit of the test channel showed monotonous increase of the loss while its profile was kept very similar with the injection pressure. The area indicating the loss and the presence of H2 gas almost coincided with each other, which remained to be small to indicate very slow gas mixing/diffusion with the main air flow. With the increase of airflow total temperature to 1200 K, a bulk flame was first observed at the exit section. Further increase up to 1460 K observed an ignition flame at the injector. However,the reflection of the bow shock wave was found to be a more likely trigger of the bulk flame ignition within the test section.
文摘Hydrogen gas has been injected transversely into Mach 1.8 airflow between parallel channel walls from two circular sonic injectors which were mounted flush and placed in tandem along the centre line of the bottom wall plate of a test section. Both cold and hot airnow conditions, i.e. atmospheric and heated to max.1460K total temperature, were tested. In the cold flow experiments, detailed measurements were successful and the tandem injection resulted in a marked difference from the single injection with respect to the pattern of shock waves and the distribution of pressure and hydrogen concentration near the injector region. Upon changing the injection pressure ratio between the two injectors, it has been revealed that a prior injection upstream of the main injection would be beneficial in terms of the total pressure loss in the airflow and the hydrogen concentration near the injector region while maintaining the mixing performance. In general, the flow features showed little difference as the airflow temperature was raised until hydrogen burning was observed, whence the results became inevitably less quantitative. Against the expectation from the cold flow tests, a prior injection of cold hydrogen has resulted in quenching the main injector flame.
