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A new fuel injection system with a solenoid actuator was developed to reduce jet stabilization times and was compared to a conventional fuel injection system using a fast-acting valve. The jet stabilization time was examined from free-jet images obtained using a flow visualization technique. Using a supersonic wind tunnel, the jet establishment image and trajectory for supersonic flows were obtained. The jet stabilization times were obtained at fuel tank pressures of 500, 700, and 900 kPa and injection orifice diameters of 1 and 2 mm. For all cases, the jets were stabilized at 4–12 ms, which was shorter than the stabilization time (approximately 300 ms) of the conventional system. The injection pressure measurements and jet trajectory comparison showed that the new system could inject fuel at the target pressure more effectively than the conventional fuel system. [ABSTRACT FROM AUTHOR]

Ablation behaviors of laminated carbon fiber reinforced plastics (CFRP) subjected to intense continuous wave laser in the supersonic wind tunnel are investigated experimentally. Comparable laser ablation tests in other environments, i.e., static air, static nitrogen and open airflow, are also carried out. Laser ablation rate in the supersonic wind tunnel is significantly larger than those of the other environments, in particular, at least twice of that in an open tangential airflow condition. The ablation morphology can be classified into two regions, coupled ablation zone (CAZ) and downstream affected zone (DAZ). Coupled thermal-fluid-solid analysis including thermochemical ablation and thermomechanical erosion models reveals that the contribution of each laser mechanisms is distinctive at the different positions of the laser ablation pit.

Programs in mechanical and aeronautical engineering commonly include courses in compressible fluid flow. As such, learning can be greatly enhanced if theory is taught in conjunction with hands on experimentation. While supersonic wind tunnels are not uncommon at many universities, such facilities are generally of the blow down configuration. Consequently, run time is very short and ear protection is required during operation, potentially hindering instruction. Furthermore, blow down configurations are typically expensive and large. This article presents the design and manufacture of a continuous, indraft, miniature supersonic wind tunnel. The tunnel was designed for a nominal test section Mach number of 2; validation indicated a Mach number of 1.96 was achieved. Vacuum was provided by a regenerative blower. The facility is portable and quiet; measurements indicated that the sound level around the tunnel when operational was less than 81 dB (compared to 119dB generated by the department's blow down supersonic wind tunnel). [ABSTRACT FROM AUTHOR]

This study presents part-II of the work-in-progress for the development of a high-speed wind tunnel under the EU Commission (ERDF) project. This study was carried out after the inlet section of the supersonic wind tunnel prototype had been designed in part-I [1] by introducing a simplified design approach of "table of inclination". The design optimization of the exhaust section, i.e., diffuser of the wind tunnel is the main objective of the current study. Diffuser design optimization was carried out in three steps; at first, the selection of the diffuser type was carried out and the initial estimated design was created. In the next step, 2D optimization of the wind tunnel design was carried out, and finally, 3D optimization of the complete wind tunnel model was performed. The main geometric parameters of diffuser design were optimized using CFD analysis. Due to the proposed design optimization strategy, the conventionally long diffuser length was successfully reduced. Additionally, 3D optimization further improved the design and helped to resolve the problem of higher operating power. This compact wind tunnel duct will have relatively lower manufacturing costs as well as the overall testing facility will occupy a smaller space. The optimized design of the diffuser and its integration with the inlet section of the wind tunnel marked the completion of the design of the full wind tunnel duct. [ABSTRACT FROM AUTHOR]

This study aims to develop a simplified approach for the design of high-speed wind tunnels, operating within the range of Mach 1-4. The study is conducted in two stages; design stage-I consists of the basic parts of a high-speed wind tunnel, i.e. test section and nozzle throat sizes along with the calculations of the minimum pressure ratios necessary for the starting and running of the wind tunnel. Design stage-II is the aerodynamic design of the inlet nozzle contour with the focus on the divergent nozzle section only. In this stage, the fundamental method of characteristics (MOC) is employed by using region-to-region solution approach. Due to the long and complicated procedure of classical MOC, a simpler approach of "table of inclination" is proposed. This inclination table approach is simple in use, highly precise, and efficient which reduces more than 75 % of the calculation time of the MOC. Validation of the nozzle contour design is performed with the Area-Mach ratio relation followed by the results verification obtained from the MATLAB programming. The contour design results of the study are highly accurate (less than 1 % error) which manifests the future possible significance of the inclination table approach for supersonic wind tunnel designs. [ABSTRACT FROM AUTHOR]

The peculiarities of supersonic unsteady flows forming in the processes of an impulse starting of a wind tunnel including a fore-chamber, a nozzle, a diffuser, and an exhaust tank are considered. The fore-chamber is separated from the flow duct by a thin breakable diaphragm. Before the wind tunnel starting, the gas contained in the exhaust tank is pumped out down to a very small pressure, and then the high-pressured working gas is fed into the fore-chamber. Upon reaching some value of this pressure, the diaphragm "instantaneously" ruptures, and the working gas starts exhausting through the nozzle: a rapid unsteady process of the wind tunnel starting arises. The numerical simulation of the flows forming at the impulse starting of the simplest experimental gas-dynamic facility has been carried out; the facility is arranged with a nozzle forming at its exit a two-dimensional supersonic flow with the Mach number of 2.9, and with replaceable diffusers having different relative areas of the throat. The numerical computations of two-dimensional unsteady flows have been carried out using the Reynolds-averaged Navier—Stokes equations and the SST k-ω turbulence model. The flow patterns computed numerically are compared with the data of the optical visualization of the flow obtained in the experimental gas-dynamic facility in the process of its starting. [ABSTRACT FROM AUTHOR]

Supersonic wind tunnel is regarded the most efficient experimental facility for studying the performance of supersonic inlets. In view of this background, the starting problem of a wind tunnel coupled with the inlet model is a critical experimental issue. However, inlet experiments cannot be performed when wind tunnels do not start. To satisfy this requirement, this study adopts numerical simulations to examine the starting characteristics of a wind tunnel coupled with the inlet model to serve as a basis for observing the flow at the starting procedure. Results of steady simulation show that the wind tunnel coupled with the medium-sized inlet model is still at risk in the starting procedure, although the inlet size of the model is considerably smaller than the physical limitation. Furthermore, imposing high total pressure on the wind tunnel inlet can make the wind tunnel restart. However, results also reveal that gradually increasing total pressure does not necessarily restart the wind tunnel, as wind tunnels can start only when total pressure amplitude is large enough. To improve the understanding of the phenomena, unsteady numerical simulations with different total pressure levels are performed on the wind tunnel inlet. Numerical results demonstrate the importance of generating a moving shock wave with adequate intensity that can overcome the structure of the separation zones near wind tunnel walls after sweeping the inlet model. Under this influence, the separation zones become relatively smaller, thereby weakening the intensity of the deduced shock wave. Several changes to improve the startup of the wind tunnel are also observed, such as the attachment of the detached shock wave mechanism situated in front of the inlet model and the disappearance of the shock wave/boundary-layer interactions near the lower wall. These changes can reduce total pressure loss in the wind tunnel and prompt the wind tunnel to restart. In conclusion, a sudden increase in total pressure can easily start the wind tunnel. The valve of the wind tunnel should therefore be opened rapidly regardless whether the wind tunnel is in the starting or non-starting procedure. [ABSTRACT FROM AUTHOR]

An experimental study has been conducted to investigate the flow characteristics over two rounded contour bumps. Vane-type vortex generators or longitudinal aligned passive by-pass jets were implemented in attempt to achieve wake flow control in rounded contour bumps. According to the results collected from the surface oil flow visualisation experiments, it was observed that the use of both the vane-type vortex generators and the longitudinally aligned passive by-pass jet could reduce the size of the spanwise vortices in the bump valley. In addition, a pair of streamwise horseshoe vortices was observed downstream of the bump crest of the contour bump that equipped with the vane-type vortex generators. From the data collected in the particle image velocimetry measurements, it was found that the use of both the vane-type vortex generators and the longitudinally aligned passive by-pass jet could not reduce the size of the wake region but they could reduce its strength. It is deduced that the two streamwise horseshoe vortices generated by the vane-type vortex generators enhance flow mixing which results in reducing the strength of the wake region. In contrast, blowing passive by-pass jet in the bump valley increases the local flow velocity in order to reduce the strength of the wake region. [ABSTRACT FROM AUTHOR]

An experimental study has been conducted to visualise the instantaneous streamwise and spanwise flow patterns of a normal shock wave impinging over a rounded contour bump in a Mach 1.3 free-stream. A quartz-made transparent shock generator was used, so that instantaneous images could be captured during the oil-flow visualisation experiments. Fluorescent oil with three different colours was used in the surface oil-flow visualisation experiment to enhance the visualisation of flow mixing and complicated flow features that present in the flow field. Experimental data showed that the rounded contour bump could split the impinging normal shock wave into a or a series of lambda-shaped shock wave structure(s). In addition, it was found that the flow pattern and the shock wave structures that appeared over the rounded contour bump depended highly on the impinging location of the normal shock wave. The flow pattern shown in this study agreed with the findings documented in literature. Moreover, it was observed from the instantaneous oil streaks that the normal shock impinging location also affected the size and the formation location of the spanwise counter-rotating vortices downstream of the bump crest. Finally, it was concluded that the terminating shock could distort the oil streaks that left over the surface of the contour bump. Therefore, the use of the transparent normal shock wave generator is recommended when conducting experiments with normal shock wave impingement involved. Graphical abstract: [ABSTRACT FROM AUTHOR]