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The influence of the thermal wake due to pulsating optical discharge on the aerodynamic-drag force
摘要： The influence of a thermal wake due to gas injection and due to a pulsating optical discharge (POD) on the aerodynamic-drag force of a body in a supersonic air flow with Mach number M = 1.45 are experimentally examined. With the help of a single-component aerodynamic balance, the influence of the injected subsonic jet and the thermal wake produced by POD on the aerodynamic drag of a hemisphere-on-cylinder model was studied. It is shown that the observed aerodynamic-force reduction phenomenon can be made more pronounced by increasing the laser power and pulse repetition frequency, or by decreasing the distance between the model and the pulsating optical discharge. The maximum aerodynamic-force reduction (up to 15%) due to the thermal-wake action was observed at a maximum laser-radiation power of W = 2.3 kW and at a pulse rate of f = 90 kHz. The joint effect due to the argon jet and due to the POD caused an aerodynamic-drag force reduction reaching 30%.
关键词： thermal wake,gas injection,CO2-laser,supersonic flow,pulsating optical discharge,aerodynamic-drag force
更新于2025-09-23 15:23:52
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Skin Friction Measurements Using Oil Film Interferometry in a 3-D Supersonic Flowfield
摘要： The application of oil film interferometry (OFI) for the measurement of global skin friction on the surface beneath a complex three-dimensional supersonic flow is explored in this study. The flowfield is produced by a fin-generated oblique shock interacting with a compressible turbulent boundary layer. Measurements were obtained by modifying a comprehensive acquisition and processing software, previously developed for two-dimensional, low-speed flows, to measure skin friction distributions underneath such flows. This approach required the local flow direction on the surface, and therefore traditional oil flow visualization was coupled with OFI measurements. A cross-correlation-based algorithm was incorporated to extract flow direction from sequences of oil flow visualization images. Photogrammetry was used with both surface oil flow and OFI to ensure proper spatial overlap for the two measurements. Results from this study demonstrate the capability of the approach in a complex, supersonic flow field that contains regions of both separation and reattachment concomitant with a wide range of skin friction values. The skin friction results show excellent homogeneity, standard deviation of 5.1% of the mean, in the undisturbed boundary layer upstream of the interaction and capture well-resolved high shear gradients in the interaction region. A comparison to legacy data from a similar interaction shows matching trends within the developed flow.
关键词： three-dimensional flow,shock boundary-layer interaction,supersonic flow,oil film interferometry,skin friction
更新于2025-09-23 15:22:29
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Development of low vacuum laser welding technique using an aerodynamic window; ??o????a?????????¨???????????§??°?￠?????????????????o???￥???è??é????o;
摘要： In order to realize deep laser welding, conceptual application of a supersonic jet as an aerodynamic window was investigated. Detailed characteristics of the supersonic jet as the aerodynamic window were studied experimentally. Flow field of the supersonic jet was examined based on the schlieren flow visualization technique. As compared to a free-vortex flow design applied to the aerodynamic window nozzle, in the case of supersonic jet, oblique shock waves were captured both at the nozzle exit edge and the shear layer on the aerodynamic window. The velocity field under the condition that the shock-expansion wave was formed in the aerodynamic window was measured by the PIV (Particle Image Velocimetry) system (Koncerto II, Seika Digital Image Corp.). Both the vorticity magnitude and angular momentum were analyzed. Level of the vorticity magnitude in the core region of the supersonic jet was smaller by one-order than that in the shear layer in the region corresponding to the passage of laser-light (θ = 30 to 40° and r = 23.8 to 27.1 mm). The radial and circumferential velocity product in this region was similar to that observed under the free-vortex condition. In addition to the measurement mentioned above, pressure behavior was investigated using a multi-pressure measuring system (Scanivalve Corp. ZOC33). When the reservoir pressure was set at 800 kPa and diffuser width as 30.0mm, cavity pressure was reduced to 10.0 kPa. Under this reduced pressure environment, penetration depth increased by 2.6 times compared to penetration depth under atmospheric pressure environment. The effectiveness of the supersonic free-vortex aerodynamic window system tested in the high power laser welding manufacturing has been proven by the present study.
关键词： PIV,Aerodynamic window,High power laser welding,Flow visualization,Supersonic flow,Schlieren
更新于2025-09-23 15:21:01
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Dynamics of dual-pulse laser energy deposition in a supersonic flow
摘要： Dynamics of plasma generated by the dual-pulse laser in a supersonic flow was studied numerically. The mathematical model includes species, momentum, electronic, vibrational and translational energy equations for the multicomponent ionized air. The model examines temporal dynamics of the formed air plasma and how it affects the drag, pressure signature and vorticity generation in a supersonic flow around a wedge. We observed that nonequilibrium plasmas is more effective in the drag reduction compared with the simultaneous thermal energy addition. The maximum drag reduction of around 50% and the maximum drag coefficient reduction of 30% was attained through the dual-pulse laser energy deposition. Variation of the plasma spot orientation did not significantly influence the drag reduction. We suggested that the surface pressure changes were not controlled by the vorticity generation but occurred due to the density changes and the formation of the low–density plasma spot.
关键词： supersonic flow control,energy deposition,laser,numerical modeling
更新于2025-09-23 15:19:57
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Application of laser energy deposition to improve performance for high speed intakes
摘要： Research interest has been growing in recent years in supersonic transport, particularly supersonic propulsion systems. A key component of a commonly studied propulsion system, ramjets, is the air intake. For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery. This refers to the ratio of the average total pressure after the intake to that of the freestream. One phenomenon that can have a large effect on this performance index is flow separation at the inlet. The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet. This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel. Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ. Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance. Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone. Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake. At the optimal laser frequency, found for this Mach number to be 10 kHz, the pressure recovery is found to increase by up to 4.7%. When the laser power added to the system is considered, this results in an overall increase in propulsive power of 2.47%.
关键词： Intakes,Supersonic,Flow dynamics,Flow separation,Laser energy deposition
更新于2025-09-16 10:30:52
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Slow sound laser in lined flow ducts
摘要： This work considers the propagation of sound in a waveguide with an impedance wall. In the low frequency regime, the first effect of the impedance is to decrease the propagation speed of acoustic waves. Therefore, a flow in the duct can exceed the wave propagation speed at low Mach numbers, making it effectively supersonic. This work analyzes a setup where the impedance along the wall varies such that the duct is supersonic then subsonic in a finite region and supersonic again. In this specific configuration, the subsonic region acts as a resonant cavity, and triggers a laser-like instability. This work shows that the instability is highly subwavelength. Besides, if the subsonic region is small enough, the instability is static. This work also analyzes the effect of a shear flow layer near the impedance wall. Although its presence significantly alters the instability, its main properties are maintained. This work points out the analogy between the present instability and a similar one in fluid analogues of black holes known as the black hole laser.
关键词： impedance wall,slow sound,black hole laser,supersonic flow,laser instability,subsonic flow
更新于2025-09-11 14:15:04
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Effects of Laser Energy Deposition on the Transition Characteristics of Shock Reflection in the Dual Solution Domain
摘要： Numerical simulations were conducted to investigate the transitional characteristics of shock reflections in the dual solution region using laser energy deposition. The numerical approach was validated by comparison to experimental results of the deposition laser energy in front of a blunt model. The simulation results show that the energy deposition in the freestream region can induce a transition of the shock reflection system and the transition characteristics can vary with the position and energy of the laser deposition. As the amount of energy increases, the time required for the transition also increases, and the transition cannot occur when the energy that is applied exceeds a certain level. The time required for the transition can be reduced when the position of energy deposition is moved downstream. The results also show that the transition does not occur regardless of the deposited energy when the laser energy is deposited on the symmetry line.
关键词： shock reflection transition,flow control,laser deposition,supersonic flow
更新于2025-09-11 14:15:04