Choked flow of low density gas in a narrow parallel-plate channel with adiabatic walls

The estimation of the gaseous leak flow rates through a narrow crack is important for a leak-before-break analysis as a method of nondestructive testing. Therefore, the methodology to estimate the gaseous leak flow rates in a narrow crack for a wide range of flow conditions, from no-slip to slip flow and from unchoked to choked flow, by using f. Re (the product of friction factor and Reynolds number) correlations obtained for a microchannel, was developed and presented. The correlations applied here were proposed by the previous study (Hong, et al., 2007, "Friction Factor Correlations for Gas Flow in Slip Flow Regime," ASME J. Fluids Eng., 129, pp. 1268-1276). The detail of the calculation procedure was appropriately documented. The fourth-order Runge—Kutta method was employed to integrate the nonlinear ordinary differential equation for the pressure, and the regular-Falsi method was employed to find the inlet Mach number An idealized crack, whose opening displacement ranges from 2 μm to 50 μm, with the crack aspect ratio of 200, 1000, and 2000, was chosen for sample estimation. The present results were compared with both numerical simulations and available experimental measurements. The results were in excellent agreement. Therefore, the gaseous leak flow rates can be correctly predicted by using the proposed methodology.

Estimation of Leak Flow Rates Through Narrow Cracks

: Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature is extracted by fitting the recorded signal with a theoretical signal constructed from the Doppler-broadened hyperfine components of the ro-vibrational line. The CBIMF technique proved successful for extracting the temperature of an I2-seeded, Ar gas flow within a small, Mach 2, Laval nozzle where the overlap volume of the two 1 mm diameter laser beams was 2.4 mm3. At a test point downstream of the nozzle throat, the average temperature of 146 K +/- 1.5 K extracted from measurements of the I2 P(46) 17-1 spectral line compared favorably with the 138 K temperature calculated from isentropic, one-dimensional flow theory.

Spatially-Resolved Temperature Diagnostic for Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy

The flow of a rarefied gas through rectangular configuratons of different geometries has been experimentally studied to determine their discharge coefficient characteristics. The configurations used are a set of sharp-edged slit orifices, a smooth converging nozzle and a tube. The range of the Reynolds number based on the throat conditions varied from 0.01 to 100. The equivalent Knudsen number range based on the upstream conditions and inlet diameter varied from 0.0521 to 2.521. The results for the smooth nozzle are compared with calculations using a numerical method with one-dimensional stream tube approximation based on integrated boundary layer equations. The slit and the tube results are compared with the experimental results of Sreekanth and Davis [1988].

Experimental investigation of rarefied gas flow through rectangular slits and nozzles

This paper deals with the two-dimensional Collisions of vehicles. The authors have already analysed the vehicle collisions in consideration of vehicle movements during impact. In those studies tire forces acting in the duration of impact were not considered. However, it does not seem that they can be ignored under any impact condition. In the present paper, therefore, the authors introduce the impact forces acting between two vehicle bodies and tire forces acting from the road into the equations of motion of four-wheel vehicles and analyse the vehicle motion throughout the vehicle collisions (pre-impact. impact and post-impact vehicle motion). Finally, they compared the results obtained from the present method with those obtained from the method ignoring tire forces acting in the duration of impact. It is shown from the comparisons that tire forces acting in the duration of impact affect the vehicle velocities after impact and the vehicle trajectories are not predicted correctly if they are negle...

Two-dimensional collisions of vehicles (case of consideration of tire forces during impact)

Low-density choked flow through a parallel plate channel with a narrow gap is studied experimentally for a wide range of Reynolds numbers. In the region from continuum flow to slip flow, the choked flow is analyzed by one-dimensional flow approximation based on the integrated boundary layer equations, taking into account the slip at the channel walls. The calculated discharge coefficients and pressure distributions agree well with the experimental results for a wide range of Reynolds numbers, including the slip flow region. A nondimensional correlation equation of the discharge coefficient is proposed as a function of Reh s /l for Reh s /l<2x10 2 . In the region from slip flow to molecular flow, the experimental results agree well with those of previous work. A nondimensional correlation equation of C d l/h s is proposed as a function of Re for 7 < Re < 5 x 10'.

Discharge Characteristics of Low-Density Gas Flow through Parallel Plate Channel with Narrow Gap

Discharge Characteristics of Low-Density Gas Flow through a 2-Dimensional Convergent-Divergent Nozzle

Axial velocity distribution in an I2-seeded Ar free jet is investigated by the laser-induced fluorescence(LIF)technique using a ring dye laser with 500 kHz line width. Since the translational temperature in the flow region is low, the hyperfine structure due to the nuclear spin of I2 molecules is observed in the spectrum of I2 B-X bands. The spectrum shape is explained by the quantum mechanical theory and the simulated spectra coincide with our measurements. First, the possibility of the translational temperature measurement based on the hyperfine spectrum shape is discussed. Then, axial velocity measurement is performed and the results are found to be in good agreement with those of Ashkenas & Sherman. The applicability and the velocity resolution limit of our measurement technique are also discussed.

Etsuro Hirai

Papers

Discharge Characteristics of Low-Density Gas Flow through Parallel Plate Channel with Narrow Gap

Discharge Characteristics of Low-Density Gas Flow through a 2-Dimensional Convergent-Divergent Nozzle

Velocity measurement of free jets using nuclear hyperfine structure of I2