James Moller

Interpretation of Gas Turbine Response Due to Dust Ingestion

A measurement program currently underway at Arvin/Calspan Advanced Technology Center has been used in the evaluation of observed engine behavior during dust ingestion. The Pratt and Whitney TF33 turbofan and J57 turbojet were used in the investigation. Solid particle ingestion was found to erode the compressor blades and result in substantial performance deterioration. The engines were found to have increased susceptibility to surge at low power settings. The roles that anti-ice and intercompressor bleed airplay in surge avoidance are discussed. A discussion of the fuel controller behavior in a deteriorated engine and its effect during steady-state engine operation is also presented. Experimental data obtained during testing were compared to a predictive capability developed to describe deteriorated engine response. The effects of tip clearance, blade profile, and secondary flows were taken into account. The results show good agreement with experimentally observed engine behavior.

Bond breaking in stretched molecules: multi-reference methods versus density functional theory

Several quantum chemistry methods were compared for modeling the breaking of bonds in small molecules subjected to extreme strain. This provides a rigorous test of quantum mechanical methods because a high degree of dynamical and non-dynamical correlation is required to accurately model bond breaking in a strained molecule. The methods tested included multi-reference methods, unrestricted Kohn–Sham density functional theory (DFT) using several functionals, and unrestricted coupled-cluster singles and doubles. It is challenging to employ the multi-reference method in a balanced way for the molecules considered due to the computational cost. While the DFT methods are less costly and provide balanced correlation, they do not have enough static correlation to properly model the bond-breaking curve to dissociation. Despite this, for the N12 DFT method the artifacts due to spin contamination of the unrestricted Kohn–Sham method were the least severe and tolerable. Given this, and the low computational cost, the N12 method was chosen for subsequent dynamical simulations for modeling fracture inception in polymers under extreme strain. The physical characteristics of the bond-breaking process are discussed as well as the influence of secondary conjugation on the process.

Aqueous foam drainage characterized by terahertz spectroscopy.

Aqueous foam drainage has been studied using terahertz (THz) spectroscopy. Water is highly absorbing of THz radiation, allowing drainage to be determined based on water content at respective foam height. These drainage profiles were validated using a model constructed from published equations and tailored to this specific study. In addition, a slow-draining foam was scanned to produce a two-dimensional foam image.

Prediction of Incipient Nano-Scale Rupture for Thermosets in Plane Stress

There is limited experimental evidence that fracture nucleation in polymers includes a small number of covalent bond scissions followed by rapid void growth by chemo-mechanical processes. Generalized criteria for predicting such bond scission, then, would help anticipate fracture in polymer matrix composites. Strain states at incipient bond scission for thermoset resins in plane stress are here predicted by atomistic simulation. Several cured epoxy systems were examined, each having a different chain length. For biaxial extension and a portion of the shearing regime, scission occurs at a critical value of the larger principal strain. This value increases with increasing chain length. The corresponding dilatation is largest for biaxial extension and decreases to nearly zero for pure shear. Results are compared with strain invariants at fracture measured from experiments in which polymer matrix composites having various ply stacking sequences were loaded to rupture.

Development of a new high-enthalpy shock tunnel

This paper describes the design of a new highthe pages of the symposia on Shock Tubes and Waves, enthalpy shock tunnel currently being planned at Calspan. the Journal of the Aerospace Sciences and the Journal The facility is to be assembled from an existing Gin. of the American Rocket S a i e t y (the AIAA Journal), and inside diameter shock tube and a ye t to be constructed the Physics of Fluids to have access to most of these contoured expansion nozzle and driver tube. The facility efforts. For the purposes of this paper, some of the is desiened to o w r a t e in the reflected-shock mode and Previous work aermane to the shock-lunnel d e s k to p r o k c a maximum reflected shock enthalpy level on the order of .5 x IO4 Btullb a t a corresponding prtssure The available test time in the reflected-shock reservoir at this peak enthalpy level is on the order of 0.2 ms. The driver tube of this facility is designed for 40,000 psi at 75OoF which provides the capability for very high Reynolds numbers at intermediate enthalpy levels in the expansion flow. In addition, because of the large shocktube diameter, a relatively large nozzle throat can be utilized.

Bond breaking in epoxy systems: A combined QM/MM approach.

A novel method to combine quantum mechanics (QM) and molecular mechanics has been developed to accurately and efficiently account for covalent bond breaking in polymer systems under high strain without the use of predetermined break locations. Use of this method will provide a better fundamental understanding of the mechano-chemical origins of fracture in thermosets. Since classical force fields cannot accurately account for bond breaking, and QM is too demanding to simulate large systems, a hybrid approach is required. In the method presented here, strain is applied to the system using a classical force field, and all bond lengths are monitored. When a bond is stretched past a threshold value, a zone surrounding the bond is used in a QM energy minimization to determine which, if any, bonds break. The QM results are then used to reconstitute the system to continue the classical simulation at progressively larger strain until another QM calculation is triggered. In this way, a QM calculation is only computed when and where needed, allowing for efficient simulations. A robust QM method for energy minimization has been determined, as well as appropriate values for the QM zone size and the threshold bond length. Compute times do not differ dramatically from classical molecular mechanical simulations.