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This paper discusses that the unsteady aerodynamic forces caused by vehicle motion in road input have a large influence on the vehicle behaviors. In the present coupling analysis, unsteady aerodynamic forces were obtained by using the response functions for vehicle motion derived in our previous study. By attaching a protrusion on the roof which only measures about 3% of the vehicle height, pitch and heave motions are affected significantly by the change of unsteady aerodynamic effects. Due to the coupling of the unsteady aerodynamic forces and vehicle suspension responses, the vehicle behavior depends on the road input frequency. The pitch motion is enhanced in low-frequency road input (1.6 Hz). Meanwhile, the heave motion is suppressed over 1.2 Hz. Such vehicle behaviors were verified in actual running tests, and were consistent to the subjective evaluation of the drivers feeling. Comparing the unsteady aerodynamic coefficients to the equivalent vehicle specification factors, the aerodynamic inertia caused by pitch motion contributes to 39% of the rear vehicle mass inertia effect in pitch motion. This aerodynamic effect is important in designing suspension specifications of vehicles. These results show that the vehicle stability can be affected even by small detail in vehicle shape due to the unsteady aerodynamic forces.

In this study, unsteady aerodynamic forces induced by forced pitch and heave motions are measured and formulated to the unsteady aerodynamic coefficients by utilizing the 1/4-scale nearly actual vehicle model with wheels and wheel-houses and a system without unnecessary stings exposed to the flow. The unsteady aerodynamic lift forces are measured as input forces at front and rear axles in vehicle suspensions for each, and are expressed as the aerodynamic inerter, aerodynamic damping and aerodynamic spring coefficients which are equivalent in vehicle suspension property. These studies are conducted with less than 1.4 × 106 of Reynolds number and with less than 0.2 of non-dimensional frequency. From the results, it is observed the effect of front aerodynamic forces in proportion to motion acceleration which works as an inerter can be ignored in both of pitch and heave motion, but the effect of rear aerodynamic forces as an inerter must be considered in both motion, and the first-order lag must be considered additionally about the rear only in heave motion. Furthermore, the large difference of unsteady aerodynamic characteristics is obtained while comparing in different vehicle body shapes which are without and with a protrusion on the roof. Especially, the difference of unsteady aerodynamic forces of rear in pitch motion is much large. In the case without the protrusion, the aerodynamic inerter which restrains pitch motion is occurred. On the other hand, in the case with the protrusion, the effect of aerodynamic inerter decreases and other aerodynamic forces promotes pitch motion in opposite. The phenomenon of this difference is closely related to the behavior of flow velocities at near surface around the model. From the above, it is confirmed that the large difference of unsteady aerodynamic forces induced by motions occurs in the detail difference of body shapes at a nearly actual vehicle model, and can be expressed quantitatively as the difference of aerodynamic response.

A high-pressure field is generated in a circular tube by introducing an unsteady jet from its open end. The head of this jet acts as a piston, driving compression waves ahead of it. The peak value of the induced overpressure is evaluated as a solution of a Riemann problem, wherein the jet head is equivalent to a piston head. The jet head of the driver gas, with a filling pressure of 400 kPa, is equivalent to a piston head moving at 160 m/s. This high-pressure generation scheme through the “piston effect” is useful for industrial applications, including filter cleaning in dust collectors, and as an interesting example of unsteady, compressible fluid dynamics.

The effect of repetitive energy deposition on low Strouhal number oscillations of the shock wave induced by boundary-layer interaction over a cylinder-flare model was studied. The fluctuation of the energy deposition frequency was induced in the flow, because the bubble generated by the energy deposition flowed downstream along the surface repeatedly. The region before the bubble size was affected by the energy deposition directly, so the fluctuation frequency was equal to the energy deposition frequency. However, the flare shock behavior at a position farther from the surface than the bubble size was also affected strongly by the energy deposition. For low-frequency unsteadiness and the effect of energy deposition on its unsteadiness, two categories have been observed. In the relatively small flare angle case, the flare shock was oscillated owing to the fluctuation induced by the boundary-layer interaction at the shock foot, and its oscillation occurred at 2.1 kHz with a small amplitude. The amplitude of this oscillation was decreased by highly repetitive energy depositions, and its amplitude could not be detected at a highly repetitive energy deposition. In the longer cylinder section case, the region of the shock-wave interaction was widened, and the amplitude of the flare shock oscillation was increased. In this case, the amplitude drastically decreased because of energy deposition.

The thrust performance of a steady-state, applied-field magnetoplasmadynamics (MPD) thruster has been improved by increasing a discharge current was increased from 20 A to 60 A using a lanthanum hexaboride (LaB6) hollow cathode. The experimentally obtained thrust characteristics were consistent with that of electromagnetic acceleration. Using argon as the propellant, a thrust efficiency of 25.5% and a thrust/power ratio of 17.0 mN/kW were obtained with an applied magnetic field of 265 mT, discharge current of 30 A, propellant mass flow rate of 2.1 mg/s and discharge voltage was 121 V. [ABSTRACT FROM AUTHOR]

Supersonic drag reduction performance using repetitive pulse energy depositions over blunt bodies was experimentally studied under two Mach numbers. The normalized drag reduction and energy deposition efficiency of Mach-1.92 over a 10-mm-dia. blunt-cylinder model were 8% and 1.2 at most, respectively. On the other hand, these values at Mach-3.20 over the same model were 22% and 6.2, respectively. The shock-wave deformation period using single-pulse energy deposition at Mach-3.20 was 64 μs. This duration was shorter than that of 80 μs at Mach-1.92, but the deformation magnitude on the model center axis of 40% at Mach-3.20 was larger than that of 15% at Mach-1.92. These experimental characteristics were consistent as solutions of the Riemann problem. Moreover, a drag reduction performance was much improved with a larger model diameter of 20 mm. Therefore, it has been experimentally demonstrated that the drag reduction performance due to energy deposition improves much at a high Mach number and with large model dimensions. [ABSTRACT FROM AUTHOR]

Response time of the post-shock wave (SW) overpressure modulation by turbulence is investigated in wind tunnel experiments. A peak-overpressure fluctuation, observed on a wall, is induced by turbulence around the SW ray, but away from the wall, demonstrating finite response time of the modulation. We propose a model of the modulation based on the SW deformation by a local flow disturbance, which yields the response time being proportional to the product of the large-eddy turnover time and (MT/MS0)0.5 (MT: turbulent Mach number and MS0: shock Mach number), in consistent with the experiments. [ABSTRACT FROM AUTHOR]

The article discusses the in-tube catapult launch scheme with a well tuned in-tube model-holding condition. Topics covered include the free-flight model that needs to be separated from the sabot before reaching the muzzle, the use of controllable operation, parameters, and the use of flush-mounted pressure transducers to measure the overpressure.

The relationship between impulse and crater formation on an Al ablator with repetitive irradiation of Nd:YAG laser pulses (wavelength of 1064 nm, pulse duration of 7 ns) is investigated. The mNs level impulse is measured in a vacuum by a torsion-type impulse balance. Surface area changes caused by crater deepening are measured with a laser microscope, then used for calculating the effective fluence. The fluence is compared to a corresponding variation in the momentum-coupling coefficient with repetitive pulses. The impulse with repetitive pulses becomes undetectable because the effective fluence decreases to the ablation threshold. The momentum-coupling coefficient fits to a simple variation; that is, it sharply increases to a peak value as the effective fluence increases, then gradually decreases. [ABSTRACT FROM AUTHOR]

A ring-force balance system for a supersonic wind tunnel with a small test section was developed. This force balance system can measure an applied force independently by measuring the strain on the ring part. A theoretical analysis of this system was conducted under three conditions: an infinitesimally thin ring-force balance, a ring-force balance with finite thickness, and a ring-force balance with a support arm. From the analytical results, the azimuthal location, where the strain is zero for certain force components, varied based on the balance characteristics, such as the thickness or diameter of the ring part. A ring-force balance, which is based on this analysis, was designed and fabricated. The calibrated results showed that the designed balance was able to measure the force components with high accuracy and minimal interaction. [ABSTRACT FROM AUTHOR]

Presents a study which developed and validated experimentally a general formula on the projectile-tube wall friction force applicable to a modest-muzzle-speed and smooth-bore ballistic range where the effect of the graving is not taken into account and its effects on range performance. Background on the kinematic friction model; Experimental apparatus; Results and discussion.

In this study, the effects of thermal bubbles produced by repetitive laser pulses on a shock wave system over a cone with an apex angle of 40° surrounded by a 19 mm×19 mm square duct in a Mach 1.97 flow were experimentally investigated. The shock wave system was controlled by changing the location of the conical centerbody. Depending on the blockage condition at the center, the shock wave over the cone exhibited either a weak or strong solution; moreover, in the intermediate condition, a dual-solution domain was observed. In a critical condition, the strong shock solution of the dual-solution domain could transition into a weak shock solution even after the entry of a single thermal bubble with an energy of 5.1 mJ. In other conditions, the transition was realized only by repetitively supplying thermal bubbles with an appropriate repetition frequency. At a center, e.g., the strong-to-weak transition was achieved with a repetition frequency of 30 kHz. However, at a frequency of 50 kHz, unfavorable interactions among the thermal bubbles resulted in unsuccessful transition. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the effects of repetitive laser energy deposition using a supersonic intake model with a central conical compression surface and a 19×19  mm² cross-sectional duct in a Mach 1.92 indraft wind tunnel: especially in the subcritical and buzz modes. A single-pulse energy deposition was observed to suppress the flow separation at the compression surface by "sweeping" a shock wave system with the thermal bubble generated by the energy deposition. The duration of the sweeping effect was approximately 160  μs in the subcritical mode and 100-420  μs in the buzz mode. Furthermore, repetitive deposition of laser pulse energies was observed to moderate instabilities in both modes, and it increased the pressure recovery by as much as 8%; also, the occurrence of buzz was delayed, thereby widening the stable, subcritical regime. In both modes, there was a threshold value for the laser pulse repetition frequency fL, thd, which corresponded to the duration of the sweeping effect (e.g., fthd=6  kHz in subcritical mode). Below this frequency, the increase in the pressure was proportional to the repetition frequency; whereas above fthd, the effect per single pulse was reduced. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to examine the effects of repetitive energy deposition on the supersonic flow characteristics over a duct system with a central conical compression surface. Boundary-layer separation on the compression surface could induce flow instability in pulsation and resonant modes. At subcritical operation, this flow instability became stronger and the "big buzz" phenomenon occurred. To control these undesirable operations, repetitive laser energy deposition was done with a repetition frequency of up to 60 kHz, which resulted in a reduction of flow separation on the compression surface. It was also observed that flow oscillation characteristics at the two modes were modified; total pressure inside the duct chamber was increased and the big buzz was significantly suppressed. [ABSTRACT FROM AUTHOR]

In this study, the effectiveness of repetitive laser pulse energy deposition over a double-cone model in a Mach 1.92 flow (half-apex angles of 22 and 40 deg) was investigated experimentally. The Reynolds number, based on the model's outer diameter, was 3×105. Because of the shock wave/boundary-layer interaction, the shock wave over the cone's transition corner exhibited an inherent low-frequency oscillation with a characteristic frequency of 6.3 kHz. Using high-frequency laser deposition of up to 80 kHz, the oscillation of the shock system was suppressed. Although the boundary layer experienced "sweeping" by laser-heated rings with a primary frequency equal to that of the energy deposition, the shock system above the bubble passage experienced frequency modulation to a much lower frequency range, and the shock wave location was stabilized. [ABSTRACT FROM AUTHOR]

The article discusses research that examined the effectiveness of a staged aft body at addressing its tail boom by using an aeroballistic range. It describes the evaluation of the loudness of a sonic boom according to overpressure and the perceived loudness. The details of the experiment carried out at Nagoya University in Japan are presented. The researchers noted the generation of an expansion fan and oblique shock by the staged aft body.

The article discusses laser-pulse energy depositions as a promising scheme for wave drag reduction in high-speed flows. It says that a bow shock wave is created ahead of the flat head of the cylinder without energy deposition. According to the author, further investigations are warranted by drag-reduction performance with even higher repetition frequencies. The schematic diagram of experimental setup is also presented.