An approximate theoretical method for modeling the static thrust performance of non-axisymmetric two-dimensional convergent-divergent nozzles

An analytical/numerical method has been developed to predict the static thrust performance of non-axisymmetric, two-dimensional convergent-divergent exhaust nozzles. Thermodynamic nozzle performance effects due to over- and underexpansion are modeled using one-dimensional compressible flow theory. Boundary layer development and skin friction losses are calculated using an approximate integral momentum method based on the classic karman-Polhausen solution. Angularity effects are included with these two models in a computational Nozzle Performance Analysis Code, NPAC. In four different case studies, results from NPAC are compared to experimental data obtained from subscale nozzle testing to demonstrate the capabilities and limitations of the NPAC method. In several cases, the NPAC prediction matched experimental gross thrust efficiency data to within 0.1 percent at a design NPR, and to within 0.5 percent at off-design conditions

Support System Effects on the DLR-F6 Transport Configuration in the National Transonic Facility

An experimental investigation of the DLR-F6 generic transport configuration was conducted in the NASA NTF for use in the Drag Prediction Workshop. As data from this experimental investigation was collected, a large difference in drag values was seen between the NTF test and an ONERA test that was conducted several years ago. After much investigation, it was determined that this difference was likely due to a sting effect correction applied to the ONERA data which NTF does not use. This insight led to the present work. In this study, a computational assessment has been undertaken to investigate model support system interference effects on the DLR-F6 transport configuration. The configurations computed during this investigation were the isolated wing-body, the wing-body with the full support system (blade and sting), the wing-body with just the blade, and the wing-body with just the sting. The results from this investigation show the same trends that ONERA saw when they conducted a similar experimental investigation in the S2MA tunnel. Computational results suggest that the blade contributed an interference type of effect, the sting contributed a general blockage effect, and the full support system combined these effects

Synthetic lethal analysis of Caenorhabditis elegans posterior embryonic patterning genes identifies conserved genetic interactions

Phenotypic robustness is evidenced when single-gene mutations do not result in an obvious phenotype. It has been suggested that such phenotypic stability results from 'buffering' activities of homologous genes as well as non-homologous genes acting in parallel pathways. One approach to characterizing mechanisms of phenotypic robustness is to identify genetic interactions, specifically, double mutants where buffering is compromised. To identify interactions among genes implicated in posterior patterning of the Caenorhabditis elegans embryo, we measured synthetic lethality following RNA interference of 22 genes in 15 mutant strains. A pair of homologous T-box transcription factors (tbx-8 and tbx-9) is found to interact in both C. elegans and C. briggsae, indicating that their compensatory function is conserved. Furthermore, a muscle module is defined by transitive interactions between the MyoD homolog hlh-1, another basic helix-loop-helix transcription factor, hnd-1, and the MADS-box transcription factor unc-120. Genetic interactions within a homologous set of genes involved in vertebrate myogenesis indicate broad conservation of the muscle module and suggest that other genetic modules identified in C. elegans will be conserved

Numerical Investigation of Flow in an Over-Expanded Nozzle with Porous Surfaces

A new porous condition has been implemented in the PAB3D solver for simulating the flow over porous surfaces. The newly-added boundary condition is utilized to compute the flow field of a non-axisymmetric, convergent-divergent nozzle incorporating porous cavities for shock-boundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio of 8.78. The flow fields for a baseline nozzle (no porosity) and for a nozzle with porous surfaces (10% porosity ratio) are computed for NPR varying from 2.01 to 9.54. Computational model results indicate that the over-expanded nozzle flow was dominated by shock-induced boundary-layer separation. Porous configurations were capable of controlling off-design separation in the nozzle by encouraging stable separation of the exhaust flow. Computational simulation results, wall centerline pressure, mach contours, and thrust efficiency ratio are presented and discussed. Computed results are in excellent agreement with experimental data

The homeodomain protein PAL-1 specifies a lineage-specific regulatory network in the C. elegans embryo

Maternal and zygotic activities of the homeodomain protein PAL-1 specify the identity and maintain the development of the multipotent C blastomere lineage in the C. elegans embryo. To identify PAL-1 regulatory target genes, we used microarrays to compare transcript abundance in wild-type embryos with mutant embryos lacking a C blastomere and to mutant embryos with extra C blastomeres. pal-1-dependent C-lineage expression was verified for select candidate target genes by reporter gene analysis, though many of the target genes are expressed in additional lineages as well. The set of validated target genes includes 12 transcription factors, an uncharacterized wingless ligand and five uncharacterized genes. Phenotypic analysis demonstrates that the identified PAL-1 target genes affect specification, differentiation and morphogenesis of C-lineage cells. In particular, we show that cell fate-specific genes (or tissue identity genes) and a posterior HOX gene are activated in lineage-specific fashion. Transcription of targets is initiated in four temporal phases, which together with their spatial expression patterns leads to a model of the regulatory network specified by PAL-1

Birkhoff Normal form for Gravity Water Waves

We consider the gravity water waves system with a one-dimensional periodic interface in infinite depth, and present the proof of the rigorous reduction of these equations to their cubic Birkhoff normal form (Berti et al. in Birkhoff normal form and long-time existence for periodic gravity Water Waves. arXiv:1810.11549, 2018). This confirms a conjecture of Zakharov\u2013Dyachenko (Phys Lett A 190:144\u2013148, 1994) based on the formal Birkhoff integrability of the water waves Hamiltonian truncated at degree four. As a consequence, we also obtain a long-time stability result: periodic perturbations of a flat interface that are of size \u3b5 in a sufficiently smooth Sobolev space lead to solutions that remain regular and small up to times of order \u3b5 123

In situ effects of selected preservatives on total carbon, nitrogen and metals collected in sediment traps

The concentration and chemical composition of preservative or poison to use in sediment trap studies continue to present an important unresolved question. Past laboratory/field experiments designed to answer this question are difficult to interpret, because so-called analogs have been used instead of actual trap materials, which are compositionally complex. This paper presents our results on the in situ effects of formalin, azide and mercuric ion on material collected in MULTITRAPS set at 100 and 300 m for a period of six days in a coastal environment, and at 150 m for a period of 20.6 days in an oligotrophic environment. Effective preservative/poison concentrations used were predetermined from laboratory tests. Parameters tested for relative effects included particulate retention of C, N and selected trace metals, and the effects of the various preservatives/poisons introduced via diffusion chambers or free in solution on in situ microbial growth. In addition, the potential contaminating role of large, nonsinking zooplankton (i.e., “swimmers”) was investigated. Substantial differences between treatments were observed. Effects were not uniform, and appeared to be parameter-specific. For example, during the short-term deployment (six days), no significant differences in C flux were observed at 100 m, regardless of preservative used. Traps treated with azide yielded significantly lower N values. At 300 m (short-term deployment), and 150 m (long-term deployment), the azide treatments produced the lowest mean C and N values. Conversely, the formalin traps gave the highest C and N values relative to all treatments at these depths. In terms of metals, \u3e70% of both Cd and Mn were lost to the trap solutions, regardless of oceanic area or time deployed, while most of the Fe tended to remain in the particulate phase. Zinc, largely in association with the particulate phase over the six-day deployment, was lost to the density solution during the 20.6-day deployment, while Pb results were intermediate between these extremes. Results of the diffusion chamber experiment indicate that the formalin and mercuric ion treatments were equally effective regardless of the mode of introduction (i.e., diffusion chamber or free in solution). Azide did not appear as effective when introduced via diffusion

Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

A joint effort between the NASA Ames and Langley Research Centers was undertaken to analyze the Mach 0.745 variant of the Boeing Transonic Truss-Braced Wing (TTBW) Design. Two different flow solvers, LAVA and USM3D, were used to predict the TTBW flight performance. Sensitivity studies related to mesh resolution and numerical schemes were conducted to define best practices for this type of geometry and flow regime. Validation efforts compared the numerical simulation results of various modeling methods against experimental data taken from the NASA Ames 11-foot Unitary Wind Tunnel experimental data. The fidelity of the computational representation of the wind tunnel experiment, such as utilizing a porous wall boundary condition to model the ventilated test section, was varied to examine how different tunnel effects influence CFD predictions. LAVA and USM3D results both show an approximate 0.5 angle of attack shift from experimental lift curve data. This drove an investigation that revealed that the trailing edge of the experimental model was rounded in comparison to the CAD model, due to manufacturing tolerances, which had not been accounted for in the initial simulations of the experiment. Simulating the TTBW with an approximation of this rounded trailing-edge reduces error by approximately 60%. An accurate representation of the tested TTBW geometry, ideally including any wing twists and deflections experienced during the test under various loading conditions, will be necessary for proper validation of the CFD

Computational Analysis of the Effect of Porosity on Shock Cell Strength at Cruise

A computational flow field analysis is presented of the effect of core cowl porosity on shock cell strength for a modern separate flow nozzle at cruise conditions. The goal of this study was to identify the primary physical mechanisms by which the application of porosity can reduce shock cell strength and hence the broadband shock associated noise. The flow is simulated by solving the asymptotically steady, compressible, Reynoldsaveraged Navier-Stokes equations on a structured grid using an implicit, up-wind, flux-difference splitting finite volume scheme. The standard two-equation k - epsilon turbulence model with a linear stress representation is used with the addition of a eddy viscosity dependence on total temperature gradient normalized by local turbulence length scale. Specific issues addressed in this study were the optimal area required to weaken a shock impinging on the core cowl surface and the optimal level of porosity and placement of porous areas for reduction of the overall shock cell strength downstream. Two configurations of porosity were found to reduce downstream shock strength by approximately 50%

Synthetic Lethal Analysis of Caenorhabditis elegans Posterior Embryonic Patterning Genes Identifies Conserved Genetic Interactions

Phenotypic robustness is evidenced when single-gene mutations do not result in an obvious phenotype. It has been suggested that such phenotypic stability results from 'buffering' activities of homologous genes as well as non-homologous genes acting in parallel pathways. One approach to characterizing mechanisms of phenotypic robustness is to identify genetic interactions, specifically, double mutants where buffering is compromised. To identify interactions among genes implicated in posterior patterning of the Caenorhabditis elegans embryo, we measured synthetic lethality following RNA interference of 22 genes in 15 mutant strains. A pair of homologous T-box transcription factors (tbx-8 and tbx-9) is found to interact in both C. elegans and C. briggsae, indicating that their compensatory function is conserved. Furthermore, a muscle module is defined by transitive interactions between the MyoD homolog hlh-1, another basic helix-loop-helix transcription factor, hnd-1, and the MADS-box transcription factor unc-120. Genetic interactions within a homologous set of genes involved in vertebrate myogenesis indicate broad conservation of the muscle module and suggest that other genetic modules identified in C. elegans will be conserved.Molecular and Cellular Biolog