Experimental investigation of the base flow and base pressure of sudden expansion nozzle

This paper presents an experimental investigation of an airflow from convergent- divergent axisymmetric nozzles expanded suddenly into circular duct of larger cross- sectional area than that of nozzle exit area, focusing attention on the base pressure and the flow development in the duct. To investigate the influence of area ratios and nozzle pressure ratios on the flow field developed in the duct, the micro jets of 1 mm orifice diameter located at 900 interval along a pitch circle diameter 1.3 times the nozzle exit diameter were employed as the controller of the base pressure. The Mach number investigated in the present study was 1.87, 2.2 and 2.58. The area ratios of the present study are 2.56, 3.24, 4.84 and 6.25. The nozzle pressure ratio (NPR) used were 3 and 5. The length-to-diameter ratio of the enlarged duct was varied from 10 to 1.The level of expansion at the nozzle exit (i.e. before sudden expansion) influences the wall pressure very strongly. From the results it is observed that for NPRs 3 there is no appreciable gain in the base pressure, and hence control employed in the form of micro jets is not effective for this NPR, however, at NPR 5, there is significant change in the base pressure values for all the area ratios. This clearly indicates that the level of expansion plays an important role to dictate the value of the base pressure and ultimately the control effectiveness by the micro jets

Flow control with aero-spike behind bluff body

Flow control in high-speed is challenging due to the high-pressure shock and low-pressure recirculation bubble attached around the vehicle. Wave drag, and Base drag are important accouterments of flow around high-speed objects. This paper deals with base drag, only and presents an experimental study of aerospikes behind the base of bluff bodies to control this drag. A plate of 1 mm thickness with two spikes at 11.5 mm is placed between the nozzle and duct as a passive controller. The Mach numbers deployed for the subsonic regime were 0.6, 0.7 and for transonic regime were 0.8, 0.9 for area ratio 6.25. The L/W ratio taken were 4W, 6W, 8W and 10W. Aerospikes were found to be very effective in controlling base pressure in the transonic regime without influencing the main flow field

ACTIVE CONTROL OF BASE PRESSURE IN SUDDENLY EXPANDED FLOW FOR AREA RATIO 4.84

Abstract: Airflow from convergent-divergent axi-symmetric nozzles expanded suddenly into circular duct of larger cross-sectional area than that of nozzle exit area are studied experimentally, focusing attention on the base pressure and the flow development in the enlarged duct. Micro-jets of 1 mm orifice diameter located at 90 0 intervals along a pitch circle diameter (pcd) 1.3 times the nozzle exit diameter were employed as the controller of the base pressure. The tests are conducted for Mach numbers 1.87, 2.2 and 2.58. The area ratio of the present study is 4.84. The length-to-diameter ratio of the suddenly expanded duct is varied from 10 to 1 and nozzle pressure ratio (NPR) in the range 3 to 11. It is found that the active control in the form of blowing through small orifices (micro jets) are effective in controlling the base pressure field and even do not augment the flow field in the duct. An increase of 45 percent in base pressure was achieved for certain combination of parameters of the present study

Flow control in microfluidics devices: electro-osmotic Couette flow with joule heating effect

Purpose – Joule heating effect is a pervasive phenomenon in electro-osmotic flow because of the applied electric field and fluid electrical resistivity across the microchannels. Its effect in electro-osmotic flow field is an important mechanism to control the flow inside the microchannels and it includes numerous applications. Design/methodology/approach – This research article details the numerical investigation on alterations in the profile of stream wise velocity of simple Couette-electroosmotic flow and pressure driven electro-osmotic Couette flow by the dynamic viscosity variations happened due to the Joule heating effect throughout the dielectric fluid usually observed in various microfluidic devices. Findings – The advantages of the Joule heating effect are not only to control the velocity in microchannels but also to act as an active method to enhance the mixing efficiency. The results of numerical investigations reveal that the thermal field due to Joule heating effect causes considerable variation of dynamic viscosity across the microchannel to initiate a shear flow when EDL (Electrical Double Layer) thickness is increased and is being varied across the channel. Originality/value – This research work suggest how joule heating can be used as en effective mechanism for flow control in microfluidic devices

Evaluation of stability derivatives of an Ogive in a Newtonian limit

Stability derivatives for an ogive are obtained in the limiting case of the Mach number when it tends to infinity. The derivative in stiffness declines with the position of the pivot for the whole extent of semi-vertex angles. For half wedge angles from 20 to 25 degrees, there is a thoughtful expansion in the derivative of Stiffness. The derivative of damping declines through the pivot point for different directions of semi-vertex and accomplishes a minimal value at h = 0.75. Afterward, together with expansion in the pivot point, there is an in-direct augmentation in damping derivatives. There is a broad variation in the mathematical worth for more incredible semi-vertex perspectives in the scope of 20 degrees and above. The derivative in Stiffness increases with the angle of the semi-vertex for different varied positions of the pivot. The derivative in damping with the angle of semi vertex for varied fixed positions of pivot supposedly increases directly with the angle of semi vertex. It is additionally seen that this pattern of linear increment will, in general, get non-direct for the angle of the semi vertex in the extent of 20 degrees and past

Recent Development and Application of TiO2 Nanotubes Photocatalytic Activity for Degradation Synthetic Dyes – A Review

Synthetic dyes waste from textile industries, produce of the problematic pollutants in wastewater. TiO2 based photocatalysis are materials that exhibit excellent absorption behavior for organic compounds in wastewater due it properties including nontoxicity, high photocatalysis degradation ability, and chemical stabilities. However, several challenges exist regarding TiO2 nanotubes pure applications for dyes degradation such as poor affinity, high band gap energy, and difficulty of recovery and easy to recombination so it would decrease effectiveness of the photocatalysis process. Therefore, more design and optimization testing need to be conducted on the treatment conditions in order to reach higher removal efficiencies with lower costs. The modified physical properties by adding metal dopant, nonmetal, and sensitizer significantly enhanced photocatalysis activity. These parameters, which affect photocatalysis activity on degrade dyes waste pollutants, are discussed in the current review. As a result, the photocatalysis becomes more expected, and encourages to further research development.  Keywords: TiO2, nanotubes, degradation, synthetic, dye

Active control of base pressure in suddenly expanded flow for area ratio 4.84

Airflow from convergent-divergent axi-symmetric nozzles expanded suddenly into circular duct of larger cross-sectional area than that of nozzle exit area are studied experimentally, focusing attention on the base pressure and the flow development in the enlarged duct. Micro-jets of 1 mm orifice diameter located at 900 intervals along a pitch circle diameter (pcd) 1.3 times the nozzle exit diameter were employed as the controller of the base pressure. The tests are conducted for Mach numbers 1.87, 2.2 and 2.58. The area ratio of the present study is 4.84. The length-to-diameter ratio of the suddenly expanded duct is varied from 10 to 1 and nozzle pressure ratio (NPR) in the range 3 to 11. It is found that the active control in the form of blowing through small orifices (micro jets) are effective in controlling the base pressure field and even do not augment the flow field in the duct. An increase of 45 percent in base pressure was achieved for certain combination of parameters of the present study

Control of base flows with micro jet for area ratio of 6.25

Suddenly expanded flow with active controls in the form of micro jets has been investigated experimentally, laying emphasis on the effectiveness of micro jets on the base pressure and enlarged duct pressure field. Air injection at four locations at the base, symmetric to the nozzle axis is used as the active control. The jet Mach numbers of the present studies are 1.87, 2.2 and 2.58. The area ratio of present study is 6.25. The length-to-diameter ratio of the suddenly expanded duct and the Nozzle Pressure Ratio (NPR) are varied from 10 to 1 and 3 to 11. In addition to base pressure, wall pressure field along the duct was also studied. It is found that the active control in the form of blowing through small orifices (micro jets) are effective in controlling the base pressure field. Micro jets do not augment the flow field in the duct. As high as 55 percent, increase in base pressure was achieved for certain combination of parameters of the present study

Flow control with aerospike behind bluff body

Flow control in high-speed is challenging due to the high-pressure shock and low-pressure recirculation bubble attached around the vehicle. Wave drag, and Base drag are important accouterments of flow around high-speed objects. This paper deals with base drag, only and presents an experimental study of aerospikes behind the base of bluff bodies to control this drag. A plate of 1 mm thickness with two spikes at 11.5 mm is placed between the nozzle and duct as a passive controller. The Mach numbers deployed for the subsonic regime were 0.6, 0.7 and for transonic regime were 0.8, 0.9 for area ratio 6.25. The L/W ratio taken were 4W, 6W, 8W and 10W. Aerospikes were found to be very effective in controlling base pressure in the transonic regime without influencing the main flow field