Flow visualization and pressure measurement in micronozzles

Abstract

Micro devices have been widely used in aerospace engineering for years. Engineers are interested in applications of micro devices such as microjets, micro actuators, and micronozzles. The small size nozzles can be used for attitude adjustment and propulsion of micro-satellites or mini-spacecraft. In this paper, convergent-divergent micronozzles have been investigated at supersonic speed with various total pressures and Reynolds numbers. The throat of the micronozzle is 250 micron wide and the nozzle is designed as de Laval type. For the measurements, the Reynolds number at the throat varies from 1200 to 11000 and total pressure varies from 6 psia to 55 psia. Experimental results are obtained with pressure-sensitive paint for pressure measurement and schlieren imaging for flow visualization. Flow visualization is a challenge for conventional techniques due to the small length scales and small depth of the density gradient. A modified schlieren technique is used to increase the sensitivity by taking the ratio of wind-on and wind-off images. Pressure-sensitive paint is also used to obtain global pressure measurement of the flow field and to compare with the schlieren results.

Investigation of the double ramp in hypersonic flow using luminescent measurement systems

“…The PSP method was able to successfully capture key flow features such as bubbles of separated flow and the shock cells. Huang et al 21 applied PSP on a micro scale to study micro shock structures.…”

Schlieren Visualization of Shock Wave Phenomena over a Missile-Shaped Body at Hypersonic Mach Numbers

“…In addition, nonuniform illumination from the light source will also affect the contrast in the Schlieren image. To eliminate some of the above technical issues, the authors have followed a procedure that uses the ratio of windon and wind-off images [21] in order to get better images. The wind-off image is a reference image taken before the test.…”

The applications of pressure-sensitive paint in microfluidic systems

“…Shock wave structure is observed as the pressure drops dramatically in the divergent section under the condition of inlet pressure of 380 kPa (55 psi), and pressure ratio between inlet and exit is 3.86. The strength of the shock waves dissipates, and the boundary layer grows rapidly while the inlet pressure decreases (Huang et al 2007a). Experimental results from Nagai et al (2008) also show the Mach contour of supersonic flow in a micronozzle.…”

“…The flow fields inside microdevices have been successfully measured by Huang et al (2002), where they reported the pressure distribution inside a micronozzle device. Subsequent research applying PSP sensors in various microdevices has been conducted with microchannel, micronozzle, microcone, microjet, microturbine, and microfluidic oscillator devices (Gregory et al 2007;Guo et al 2008;Huang et al , 2007aNagai et al 2008;Osafune et al 2004). The comparison between PSP and other experimental methods applied on pressure measurements in microchannel flow is listed in Table 1.…”