Gerald C. Pham-Van-diep
University of Southern California
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Featured researches published by Gerald C. Pham-Van-diep.
Science | 1989
Gerald C. Pham-Van-diep; Daniel A. Erwin; E. P. Muntz
Molecular velocities have been measured inside a hypersonic, normal shock wave, where the gas experiences rapid changes in its macroscopic properties. As first hypothesized by Mott-Smith, but never directly observed, the molecular velocity distribution exhibits a qualitatively bimodal character that is derived from the distribution functions on either side of the shock. Quantitatively correct forms of the molecular velocity distribution function in highly nonequilibrium flows can be calculated, by means of the Direct Simulation Monte Carlo technique.
Physics of Fluids | 1991
Daniel A. Erwin; Gerald C. Pham-Van-diep; E. Phillip Muntz
One‐dimensional shock wave properties in helium and argon are predicted using Monte Carlo direct simulation. The collision model is based directly on the interatomic potential, taking angular scattering into account. The potential is assumed to be of the Maitland–Smith [n(r)−6] form. The detailed validity of the simulation is studied by comparing the predicted macroscopic and microscopic flow properties in shock waves to a wide range of available data.
Journal of Fluid Mechanics | 1991
Gerald C. Pham-Van-diep; Daniel A. Erwin; E. P. Muntz
Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulations (MCDSs) to investigate the validity of continuum theories at very low Mach numbers. Results from the Navier—Stokes and the Burnett equations are compared to MCDSs for both hard-sphere and Maxwell gases. It is found that the maximum-slope shock thicknesses are described equally well (within the MCDS computational scatter) by either of the continuum formulations for Mach numbers smaller than about 1.2. For Mach numbers greater than 1.2, the Burnett predictions are more accurate than the Navier—Stokes results. Temperature—density profile separations are best described by the Burnett equations for Mach numbers greater than about 1.3. At lower Mach numbers the MCDS scatter is too great to differentiate between the two continuum theories. For all Mach numbers above one, the shock shapes are more accurately described by the Burnett equations.
AIAA Journal | 1991
Daniel A. Erwin; Gerald C. Pham-Van-diep; William D. Deininger
The flow velocity of atomic hydrogen in the plume of an ammonia-propelled arcjet thruster was measured using laser-induced fluorescence (LIF). The velocity was obtained by the Doppler shift of the absorption peak of the Balmer α spectral line. Measurements were made at the nozzle exit, varying the distance from the plume centerline. Results are presented for arcjet operating conditions 13, 20, and 27 kW with a mass flow of 0.31 g/s
AIAA Journal | 1994
Iain D. Boyd; Gerald C. Pham-Van-diep; E. P. Muntz
The nonequilibrium flow formed by the interaction of a freejet of iodine vapor impinging on a blunt body is investigated using numerical and experimental techniques. The computational approach employs the direct simulation Monte Carlo method. The experimental measurements consist of rotational temperature obtained along the flow axis and include portions of both the freejet expansion and blunt-body shock for four different stagnation conditions. Direct comparisons of the numerical results and the experimental data are quite successful at moderate temperatures. Hence, the rotational collision time of iodine is estimated in the temperature range of 100-500 K. At higher temperatures, the agreement between simulation and measurement is less satisfactory. This demonstrates the requirement for the development of a more detailed approach to simulating rotational nonequilibrium in high-temperature flows of diatomic species. 20 refs.
25th Joint Propulsion Conference | 1989
Gerald C. Pham-Van-diep; Daniel D. Erwin; William D. Deininger; Thomas J. Pivirotto
A method for measuring the axial and transverse plume velocities and internal energy distributions in rarified thruster plumes by using pulsed laser-induced fluorescence (LIF) of atomic hydrogen Balmer lines is described. The results of an application of this technique for velocity mapping of a 30-kW ammonia arc-jet plume generated in the JPL arc-jet testing facility (which is uniquely suited for these measurements due to the end-on optical access provided by its ninety-degree-bent diffuser) are described. A schematic diagram of the JPL facility with LIF setup is included.
Archive | 1997
E. P. Muntz; Melissa E. Orme-Marmarelis; Gerald C. Pham-Van-diep; Robert J. Balog
Archive | 1991
E. P. Muntz; Daniel A. Erwin; Gerald C. Pham-Van-diep
Archive | 1989
Gerald C. Pham-Van-diep; Daniel A. Erwin
AIAA 23rd Fluid Dynamics, Plasmadynamics, and Lasers Conference, 1993 | 1993
Gerald C. Pham-Van-diep; E. P. Muntz; Iain D. Boyd