Experimental and numerical investigation of expansion corner effects on isolator performance

In the present study, the effect of expansion corner on suddenly expanded flow process has been studied. Experimental investigations have been carried out on a convergent-divergent (C-D) nozzle and isolator duct, where the expansion of the channel is formed through the presence of a 1, 2 and 3 expansion corners (EC) respectively. Flow from nozzle exit of the nozzle of Mach, M = 2.0 was suddenly expanded into the axi-symmetric duct having a cross sectional area of 4.84 times the nozzle exit area. The wall static pressure along the length of the duct and the Pitot pressure at the exit plane of the duct were measured for all the configurations. Computational fluid dynamics (CFD) technique was employed for visualizing the shock-train in the expanded duct. The isolator with one expansion corner was found to be more efficient in achieving a high static pressure rise. The experimental and numerical wall static pressure distribution values were compared for isolators with EC = 2 and found to be in good agreement with each other with a maximum absolute percentage deviation of 11%.

Supersonic jet flow control using semi-circular corrugated tabs

Purpose The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the locations of the semi-circular corrugations are varied along the leaned sides of the triangular tabs. Design/methodology/approach The tabs are fixed at the exit of the nozzle facing each other 180° apart. To quantify the jet mixing effectiveness of the semi-circular corrugated tabs, Pitot pressure measurements were carried out for the cases of over-expansion, marginally over-expansion and under-expansion levels of Mach 1.6 jet, along the jet centerline and the jet spread, along and normal to the tab axis. Findings The results exhibit that the semi-circular corrugated Tab A augments the jet mixing when compared to Tabs B and C. This impact in jet mixing is strongly due to the small-scale vortices shed from the tabs and the mixed effect of the corrugation locations and expansion ratio. The maximum percentage reduction in core length is about 73.6 per cent for the jet with semi-circular corrugated Tab A at NPR 5, whereas it is 71.4 and 67.1 per cent for Tabs B and C, respectively. Practical implications The reduction in core length of the jet with minimum thrust loss is obtained by controlling the jet used with semi-circular corrugated triangular tabs of equal blockage ratio 5.12 per cent with respect to the nozzle exit diameter. Originality/value The locations of the semi-circular corrugations varied systematically at the equally leaned sides of the triangular tab ensure the novelty of this study.

Effect of the Pitot Tube on Measurements in Supersonic Axisymmetric Underexpanded Microjets

This paper describes the results of methodical investigations of the effect of the Pitot tube on measurements of gas-dynamic parameters of supersonic axisymmetric underexpanded real and model microjets. Particular attention is paid to distortions of Pitot pressure variations on the jet axis associated with the wave structure of the jet and to distortions of the supersonic core length. In experiments with model jets escaping from nozzles with diameters ranging from 0.52 to 1.06 mm into the low-pressure chamber, the measurements are performed by the Pitot tubes 0.05 to 2 mm in diameter. The results are analyzed together with the earlier obtained data for real microjets escaping from nozzles with diameters ranging from 10 to 340 µm where the parameters of real microjets were determined by the Pitot microtube 12 µm in diameter. Interaction of the Pitot tube with an unsteady jet in the laminar-turbulent transition region is investigated; the influence of this interaction on Pitot pressure measurements is determined, and a physical interpretation of this phenomenon is provided.

Experimental Study of Single Expansion Ramp Nozzle Performance Using Pitot Pressure and Static Pressure Measurements

In order to overcome the drag at hypersonic speed, hypersonic flight vehicles require a high level of integration between the airframe and the propulsion system. Propulsion system based on scramjet engine needs a close interaction between its aerodynamics and stability. Hypersonic vehicle nozzles which are responsible for generating most of the thrust generally are fused with the vehicle afterbody influencing the thrust efficiency and vehicle stability. Single expansion ramp nozzles (SERN) produce enough thrust necessary to hypersonic flight and are the subject of analysis of this work. Flow expansion within a nozzle is naturally 3D phenomena; however, the use of side walls controls the expansion approximating it to a 2D flow confined. An experimental study of nozzle performance traditionally uses the stagnation conditions and the area ratio of the diverging section of the tunnel for approaching the combustor exit conditions. In this work, a complete hypersonic vehicle based on scramjet propulsion is installed in the test section of a hypersonic shock tunnel. Therefore, the SERN inlet conditions are the real conditions from the combustor exit. The performance of a SERN is evaluated experimentally under real conditions obtained from the combustor exit. To quantify the SERN performance parameters such as thrust, axial thrust coefficient Cfx and lift L are investigated and evaluated. The generated thrust was determined from both static and pitot pressure measurements considering the installation of side walls to approximate 2D flow. Measurements obtained by a rake show that the flow at the nozzle exit is not symmetric. Pitot and pressure measurements inside the combustion chamber show nonuniform flow condition as expected due to side wall compression and boundary layer. The total axial thrust for the nozzle obtained with the side wall is slightly higher than without it. Static pressure measurements at the centerline of the nozzle show that the residence time of the flow in the expansion section is short enough and the flow of the central region of the nozzle is not altered by the lateral expansion when nozzle configuration does not include side walls.

Influence of Different Configurations of Microjet Injection on Structure and Acoustic Radiation of Supersonic Jet

The work is devoted to experimental study of the structure and acoustic radiation of a supersonic underexpanded jet Ma = 1, Npr = 5 with the presence of vortexgenerators in the form of small-sized jets injections. Ten different configurations were tested, in which following the gas-dynamic and geometrical parameters of the microjets were changed one by one: microjets pressure, the injection distance from the main nozzle section, azimuthal, tangential, and axial angles of micronozzles inclination. The flow visualization, azimuthal Pitot pressure profiles and characteristics of jet noise in the far field were obtained. It has been revealed that the injection of microjets in general leads to an increase in the jet long-range and a decrease in its mixing. The advantageous parameters of the microjets injection for reducing the jet acoustic emission are the injection point vicinity to the main nozzle section, micronozzles inclination to main jet axis and the small tangential angle of micronozzles. The micronozzles quantity effect is non-linearly in relation to the structure and the jet noise. The average pressure measuring distribution near artificial longitudinal vortices in a jet stream cannot predict the characteristics of its mixing and acoustic radiation.

Experimental Investigation of Shape Transition Effects on Isolator Performance

Isolator is a critical component in supersonic air breathing engine and it is usually situated between the inlet and the combustor of a dual-mode ramjet/scramjet engine. In the present study, shape transition effects on isolator performance have been studied by carrying out experimental investigations on square, square to circular and square to elliptical transition ducts. The length of the isolator chosen in this study is 180 mm and the cross-sectional area of 900 mm2 is maintained constant along the length for all the ducts. Experiments were carried out for isolator inlet Mach 2, using a contoured nozzle. Varying the pressure of the settling chamber varied the expansion level at the nozzle exit, which run the nozzle. The wall static pressure along the length of the isolator and the Pitot pressure at the exit plane of the isolator were measured for all the configurations. Shadowgraph technique was employed for visualizing the shock-train in the isolator. The square to circular transition isolator is found to be more efficient in achieving the static pressure rise across the isolator than the square and square to elliptical transition ducts.

Synchronous Surface Pressure and Velocity Measurements of standard model in hypersonic flow

Experiments in the Hypersonic Wind tunnel of NUAA(NHW) present synchronous measurements of bow shockwave and surface pressure of a standard blunt rotary model (AGARD HB-2), which was carried out in order to measure the Mach-5-flow above a blunt body by PIV (Particle Image Velocimetry) as well as unsteady pressure around the rotary body. Titanium dioxide (Al2O3) Nano particles were seeded into the flow by a tailor-made container. With meticulous care designed optical path, the laser was guided into the vacuum experimental section. The transient pressure was obtained around model by using fast-responding pressure-sensitive paint (PSP)sprayed on the model. All the experimental facilities were controlled by Series Pulse Generator to ensure that the data was time related. The PIV measurements of velocities in front of the detached bow shock agreed very well with the calculated value, with less than 3% difference compared to Pitot-pressure recordings. The velocity gradient contour described in accord with the detached bow shock that showed on schlieren. The PSP results presented good agreement with the reference data from previous studies. Our work involving studies of synchronous shock-wave and pressure measurements proved to be encouraging.

Elliptic jet control with triangular tab

Elliptic jet mixing influenced by triangular tabs is demonstrated in this work. Mixing modification of a Mach 2 jet from a convergent-divergent elliptic nozzle of aspect ratio 2, in the presence of two triangular tabs along the major and minor axis at the nozzle exit, at different levels of nozzle expansion has been studied. The results show that the mixing caused by tabs along the minor axis is impressive compared to the uncontrolled jet at all the pressure ratios. But for tabs along the major axis, mixing enhancement is significant only for nozzle pressure ratios above 5. Tabs along the minor axis cause better mixing than tabs along the major axis. The iso-pitot pressure contours reveal that the tabs along the minor axis enhance the mixing by bifurcating the jet. Shadowgraphs show that the tabs render the waves in the jet weaker. The present study demonstrates the superior mixing promotion caused by triangular tab than rectangular tab, studied by Aravindh Kumar and Rathakrishnan (2015).