Nozzle Plume Research Articles

A selection limiter of DSMC for near continuum flows

A selection limiter for the direct simulation monte carlo (DSMC) method is proposed to simulate near continuum flows. The selection limiter is calculated according to a continuum breakdown parameter and is used to limit the number of potential collision pairs. A Couette flow, a supersonic flow into a pitot probe and a nozzle plume flow are studied and compared with the standard DSMC to validate present method. It is found that its computational cost is about 35% of that of the standard DSMC method with satisfactory accuracy in the near continuum regime.

Nozzle Plume Impingement on Spacecraft Surfaces: Effects of Surface Roughness

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Gas Chromatography-Microchip Atmospheric Pressure Chemical Ionization-Mass Spectrometry

An atmospheric pressure chemical ionization (APCI) microchip is presented for combining a gas chromatograph (GC) to a mass spectrometer (MS). The chip includes capillary insertion channel, stopper, vaporizer channel, nozzle and nebulizer gas inlet fabricated on the silicon wafer, and a platinum heater sputtered on a glass wafer. These two wafers are joined by anodic bonding creating a two-dimensional version of an APCI microchip. The sample from GC is directed via heated transfer line capillary to the vaporizer channel of the APCI chip. The etched nozzle forms narrow sample plume, which is ionized by an external corona discharge needle, and the ions are analyzed by a mass spectrometer. The GC-microchip APCI-MS combination provides an efficient method for qualitative and quantitative analysis. The spectra produced by microchip APCI show intensive protonated molecule and some fragmentation products as in classical chemical ionization for structure elucidation. In quantitative analysis the GC-microchip APCI-MS showed good linearity (r(2) = 0.9989) and repeatability (relative standard deviation 4.4%). The limits of detection with signal-to-noise ratio of three were between 0.5 and 2 micromol/L with MS mode using selected ion monitoring and 0.05 micromol/L with MS/MS using multiple reaction monitoring.

Analysis of Aerodynamic Interaction Flowfields around Rocket Integration System including Nozzle Exhaust Plumes

Analysis of Aerodynamic Interaction Flowfields around Rocket Integration System including Nozzle Exhaust Plumes

Computational Analysis of the Flow Field Near the Boat-tail Region of Annular Plug Nozzles.

Flow fields over annular plug nozzles are computationally simulated and the boat-tail drag characteristics are clarified and discussed based on the simulation results. The plug nozzle configuration is taken from the ATREX (Air Turbo Ramjet) engine under development at the ISAS. The simulations are carried out for the axi-symmetric nozzle configuration using compressible Navier-Stokes equations. The computed result shows that there exists a low pressure region downstream of the Prandtl-Meyer expansion on the boat-tail region and the separation shock wave appears due to the interaction of the main flow and the nozzle plume downstream. The result also shows that the primary cause of the boat-tail drag turns out to be the low pressure region downstream of the Prandtl-Meyer expansion. The flow field with the secondary flow injection is then simulated and the computed result shows that the pressure in the region in front of the separation shock wave increases and the secondary flow injection successfully reduces the boat-tail drag. The effect of the turbulence model used in the computation is discussed to ensure the reliability of the solutions.

Experiments on stability and oscillatory behavior of planar buoyant plumes

Experiments on the onset of buoyant instabilities leading to periodic formation of vortical structures in planar buoyant plumes of helium and helium/air mixtures injected into quiescent air are reported for a range of nozzle widths (w=20–70 mm), plume fluid densities (pure helium to that approaching air), and velocities at the nozzle exit. First, the plume parameters corresponding to the onset of the oscillatory instability were experimentally determined by varying the nozzle exit velocity for different nozzle widths and plume fluid densities in two different nozzle configurations. These configurations corresponded to a freestanding rectangular nozzle and a rectangular nozzle surrounded by a flat plate in the plane of the nozzle exit. The observed plume behavior in the near field was characterized as nonoscillatory, transitional, or pulsatile. The onset of pulsations in the near field of these buoyant plumes (within a height of two nozzle widths) was best correlated in terms of the plume source Reynolds number and the plume fluid to ambient density ratio. It was also found that the boundary conditions surrounding the nozzle exit had an influence on the onset of plume instability in the near field. Specifically, at a given plume to the ambient density ratio, the plumes with flat plate surround were found to transition to the oscillatory state at a lower value of the threshold velocity and therefore are less stable than the plumes originating from freestanding nozzles. Subsequently, the plume oscillation frequencies were measured as a function of plume width, plume source velocity, and the density ratio for a range of these parameters. The plume oscillation frequency was found to correlate well in terms of the nondimensional parameters, Strouhal number, S=(fw)/Vp, and Richardson number, Ri=[(ρ∞−ρp)gw]/ρ∞Vp2, yielding a correlation S=0.55Ri0.45 determined for 1<Ri<102. This correlation is somewhat different from that of the axisymmetric buoyant plumes, which can be attributed to the differences in mixing rates and the strength of the local buoyancy flux in planar and axisymmetric plumes. The vortical structures formed in the unstable plumes also exhibit several distinct vortex pair modes. The centers of the formed vortex pairs, in general, do not remain colinear and distort with respect to each other when compared with the axisymmetric plume vortex rings, which are toroidal. The convection speeds of the vortex pair centers were also measured and reported in this study.

Experiments on the oscillatory behavior of buoyant plumes of helium and helium-air mixtures

Experiments on the oscillatory behavior of axisymmetric buoyant plumes of helium and helium-air mixtures are reported for a range of nozzle diameters (3.6 cm<d<20 cm), source velocities, and plume densities. Measurements include pulsation frequencies as determined from total pressure fluctuations along the plume centerline in addition to the phase resolved laser Doppler velocity measurements. These nonreacting buoyant plumes are found to exhibit periodic oscillations of plume boundaries which subsequently evolve into toroidal vortices within one-half diameter above the nozzle exit. These oscillations and vortices are similar to those observed in pool fires, although their frequency scaling is somewhat different. The frequency relationship is well represented by the expression S=0.8Ri0.381, where the Strouhal number is S=fd/V0 and the Richardson number is defined as Ri1=[(ρ∞−ρp)gd]/ρ∞V20. Parameters f, V0, ρ are frequency, source velocity, and density and subscripts p and ∞ refer to the plume fluid and ambient, respectively. Between Ri1=100 and 500, a transition in the frequency scaling is observed as evidenced by more turbulent and vigorously mixing plumes beyond this transition. In this region, S=2.1Ri0.281. This change in scaling can be explained by the effect of turbulent mixing on local plume density and the resulting modification of the convection speed of the toroidal vortices. These results provide a consistent basis for the mechanism of the observed instability which is quite different than other types of flow instabilities. Additionally, the phase resolved velocity field of a pulsating buoyant plume reveals a strong buoyant acceleration along the plume centerline followed by a deceleration in the region of the toroidal vortex formation. The strong upward acceleration is also accompanied by significant radial inflow toward the plume centerline determining the entrainment characteristics of these pulsating buoyant plumes.

Simulation of overexpanded low-density nozzle plume flow

The direct simulation Monte Carlo method was applied to the analysis of low-density nitrogen plumes exhausting from a small converging-diverging nozzle into finite ambient pressures. Two cases were considered that simulated actual test conditions in a vacuum facility. The numerical simulations readily captured the complicated flow structure of the overexpanded plumes adjusting to the finite ambient pressures, including Mach disks and barrel-shaped shocks. The numerical simulations compared well to experimental data of Rothe.

Analysis of the two-phase flow in a de laval spray nozzle and exit plume

One method used in spray forming and coating technology involves transonic/supersonic gas-droplet two- phase flows through a de Laval nozzle and subsequent subsonic freejet flow from the nozzle to the sprayed surface. To the first- order approximation, this complex phenomenon can be treated in a quasione-dimensional manner to simulate the entire converging- diverging nozzle flow field (with particle injection at the throat) as well as the plume (freejet) region. The basic numerical technique and computer model solve the steady gas field equations through a conservative variable approach and treat the droplet phase in a Lagrangian manner, with full aerodynamic and energetic coupling between the droplets and the transport gas handled via source terms. These analyses are simple and economical to execute. The one- dimensional models are valuable in constructing algorithms for automated process control. Finally, these one- dimensional models give direction to two- and three- dimensional simulations and serve as a test bed for models based on particle dynamics and energetics.

Measurement and analysis of a small nozzle plume in vacuum

Measurements of Pitot pressure and flow angle were made in the plume of a nozzle flowing nitrogen and exhausting to a vacuum. The measurements were compared to results from a numerical simulation of the flow that was based on kinetic theory and used the direct-simulation Monte Carlo (DSMC) method. Numerical results were compared with measurements made in the plume at various axial and radial stations. Total pressure measurements were made with Pitot tubes sized for specific regions of the plume. Flow angle measurements were made with a conical probe. The measurement area for flow angle extended to 160 mm (5 exit diameters) downstream of the nozzle exit plane and radially to 60 mm (1.9 exit diameters) from the plume axis. The total pressure measurements extended 480 mm (16 exit diameters) downstream and radially to 60 mm. Comparisons of computed results from the DSMC method with measurements of flow angle displayed improved agreement with increasing distance from the exit plane. Pitot pressures computed from the DSMC method were in reasonably good agreement with experimental results over the entire measurement area.

Measured particulate behavior in a subscale solid propellant rocket motor

Particle size distributions were measured in the combustion chamber, exhaust nozzle, and exhaust plume of a small, two-dimensional rocket motor that utilized aluminized propellants. Various nozzle contours and pressures to 4.36 MPa were utilized. For pressures less than approximately 2.4 MPa, D32 of the multimodal size distributions entering the nozzle decreased with increasing pressure. Above 2.4 MPa, the higher propellant burning rates significantly reduced particle agglomeration and increased C* efficiency. At higher pressures, D32 entering the nozzle was quite small (2-6 /u.) and monomodal, and did not vary appreciably with pressure. During tailoff, D32 was significantly larger than during the steady burn, indicating another possible source for plume signature variations. Exhaust particle D32 was 1.2-1.6 /* (with a <2, 8, 28 /* trimodal distribution), independent of pressure, nozzle inlet contour, exit Mach number, degree of underexpansion, or location aft of the exit plane. The existence of a small number of larger particles indicated that either particle collision and/or surface effects occurred in the nozzle convergence, or that the larger particles at the nozzle entrance were concentrated near the wall, out of the viewing volume in the center of the flow.

A New Method of Modeling Underexpanded Exhaust Plumes for Wind Tunnel Aerodynamic Testing

A new method for modeling hot underexpanded exhaust plumes with cold model scale plumes in aerodynamic wind tunnel testing has been developed. The method is applicable to aeropropulsion testing where significant interaction between the exhaust and the free stream and aftbody may be present. The technique scales the model and nozzle external geometry, including the nozzle exit area, matches the model jet to free-stream dynamic pressure ratio to full-scale jet to free-stream dynamic pressure ratio, and matches the model thrust coefficient to full-scale thrust coefficient. The technique does not require scaling of the internal nozzle geometry. A generalized method of characteristic computer code was used to predict the plume shapes of a hot (γ = 1.2) half-scale nozzle of area ratio 3.2 and of a cold (γ = 1.4) model scale nozzle of area ratio 1.3, whose pressure ratio and area ratio were selected to satisfy the above criteria and other testing requirements. The plume shapes showed good agreement. Code validity was checked by comparing code results for cold air exhausting into a quiescent atmosphere to pilot surveys and shadowgraphs of model nozzle plumes taken in a static facility.

Flow-angle measurements in a rarefied nozzle plume

On developpe une sonde de Pitot tournante pour mesurer l'angle d'ecoulement local dans le panache resultant de la detente d'un ecoulement en tuyere dans une chambre a vide equipee d'une cryopompe

Simple Two-Dimensional-Nozzle Plume Model for Infrared Analysis

A simple modeling technique for predicting detailed flow properties in a two-dimensional (2D)-nozzle plume exhausting into quiescent air is presented. The model is constructed by splitting a scaled axisymmetric plume and inserting a rectangular section of constant-property lines in between. A semiempirical scaling factor is derived to account for differences in mixing rates between axisymmetric and nonaxisymmetric plumes. The width of the rectangular section is obtained through conservation of mass. Models have been developed for 2D convergentdivergent nozzles with and without bypass air and for 2D plug nozzles. Comparisons of total-temperature predictions with test data indicate good agreement, especially in the high-temperature core region which is the major contributor to IR signature in the plume.