Response of hot element flush wall gauges in oscillating laminar flow

The time dependent response characteristics of flush-mounted hot element gauges used as instruments to measure wall shear stress in unsteady periodic air flows were investigated. The study was initiated because anomalous results were obtained from the gauges in oscillating turbulent flows for the phase relation of the wall shear stress variation, indicating possible gauge response problems. Flat plate laminar oscillating turbulent flows characterized by a mean free stream velocity with a superposed sinusoidal variation were performed. Laminar rather than turbulent flows were studied, because a numerical solution for the phase angle between the free stream velocity and the wall shear stress variation that is known to be correct can be obtained. The focus is on comparing the phase angle indicated by the hot element gauges with corresponding numerical prediction for the phase angle, since agreement would indicate that the hot element gauges faithfully follow the true wall shear stress variation

Performance tests for the NASA Ames Research Center 20 cm x 40 cm oscillating flow wind tunnel

An evaluation is presented of initial tests conducted to assess the performance of the NASA Ames 20 cm x 40 cm oscillating flow wind tunnel. The features of the tunnel are described and two aspects of tunnel operation are discussed. The first is an assessment of the steady mainstream and boundary layer flows and the second deals with oscillating mainstream and boundary layer flows. Experimental results indicate that in steady flow the test section mainstream velocity is uniform in the flow direction and in cross section. The freestream turbulence intensity is about 0.2 percent. With minor exceptions the steady turbulent boundary layer generated on the top wall of the test section exhibits the characteristics of a zero pressure gradient turbulent boundary layer generated on a flat plate. The tunnel was designed to generate sinusoidal oscillating mainstream flows. Experiments confirm that the tunnel produces sinusoidal mainstream velocity variations for the range of frequencies (up to 15 Hz). The results of this study demonstrate that the tunnel essentially produces the flows that it was designed to produce

Quasi-circular Orbits for Spinning Binary Black Holes

Using an effective potential method we examine binary black holes where the individual holes carry spin. We trace out sequences of quasi-circular orbits and locate the innermost stable circular orbit as a function of spin. At large separations, the sequences of quasi-circular orbits match well with post-Newtonian expansions, although a clear signature of the simplifying assumption of conformal flatness is seen. The position of the ISCO is found to be strongly dependent on the magnitude of the spin on each black hole. At close separations of the holes, the effective potential method breaks down. In all cases where an ISCO could be determined, we found that an apparent horizon encompassing both holes forms for separations well inside the ISCO. Nevertheless, we argue that the formation of a common horizon is still associated with the breakdown of the effective potential method.Comment: 13 pages, 10 figures, submitted to PR

The Innermost Stable Circular Orbit of Binary Black Holes

We introduce a new method to construct solutions to the constraint equations of general relativity describing binary black holes in quasicircular orbit. Black hole pairs with arbitrary momenta can be constructed with a simple method recently suggested by Brandt and Bruegmann, and quasicircular orbits can then be found by locating a minimum in the binding energy along sequences of constant horizon area. This approach produces binary black holes in a "three-sheeted" manifold structure, as opposed to the "two-sheeted" structure in the conformal-imaging approach adopted earlier by Cook. We focus on locating the innermost stable circular orbit and compare with earlier calculations. Our results confirm those of Cook and imply that the underlying manifold structure has a very small effect on the location of the innermost stable circular orbit.Comment: 8 pages, 3 figures, RevTex, submitted to PR

Implementing an apparent-horizon finder in three dimensions

Locating apparent horizons is not only important for a complete understanding of numerically generated spacetimes, but it may also be a crucial component of the technique for evolving black-hole spacetimes accurately. A scheme proposed by Libson et al., based on expanding the location of the apparent horizon in terms of symmetric trace-free tensors, seems very promising for use with three-dimensional numerical data sets. In this paper, we generalize this scheme and perform a number of code tests to fully calibrate its behavior in black-hole spacetimes similar to those we expect to encounter in solving the binary black-hole coalescence problem. An important aspect of the generalization is that we can compute the symmetric trace-free tensor expansion to any order. This enables us to determine how far we must carry the expansion to achieve results of a desired accuracy. To accomplish this generalization, we describe a new and very convenient set of recurrence relations which apply to symmetric trace-free tensors.Comment: 14 pages (RevTeX 3.0 with 3 figures

Inner boundary conditions for black hole Initial Data derived from Isolated Horizons

We present a set of boundary conditions for solving the elliptic equations in the Initial Data Problem for space-times containing a black hole, together with a number of constraints to be satisfied by the otherwise freely specifiable standard parameters of the Conformal Thin Sandwich formulation. These conditions altogether are sufficient for the construction of a horizon that is instantaneously in equilibrium in the sense of the Isolated Horizons formalism. We then investigate the application of these conditions to the Initial Data Problem of binary black holes and discuss the relation of our analysis with other proposals that exist in the literature.Comment: 13 pages. Major general revision. Section V comparing with previous approaches restructured; discussion on the lapse boundary condition extended. Appendix with some technical details added. Version accepted for publication in Phys.Rev.

Application of shock tubes to transonic airfoil testing at high Reynolds numbers

Performance analysis of a gas-driven shock tube shows that transonic airfoil flows with chord Reynolds numbers of the order of 100 million can be produced, with limitations being imposed by the structural integrity of the facility or the model. A study of flow development over a simple circular arc airfoil at zero angle of attack was carried out in a shock tube at low and intermediate Reynolds numbers to assess the testing technique. Results obtained from schlieren photography and airfoil pressure measurements show that steady transonic flows similar to those produced for the same airfoil in a wind tunnel can be generated within the available testing time in a shock tube with properly contoured test section walls

Knowledge industry survival strategy (KISS): fundamental principles and interoperability requirements for domain specific modeling languages.

Domain Specific Languages are raising the level of abstraction of software specifications and of knowledge represen-tation in general. When DSLs are used to formalize the results of domain analysis, the result is a clean separation of concerns in the problem space. This is a major advance over aspect oriented programming, where separation of concerns is only achieved in the solution space. However, the level of interoperability between current DSL tools is comparable to the level of interoperability between CASE tools in the 90s. To increase the popularity of DSL based approaches, this needs to change. Software development has become highly decentralized, and an assumption that all parties in a global software supply chain will use identical tooling is simply not realistic. As a result today's software supply chains are much less automated than supply chains in other, more mature industries. The KISS series of workshops is used to incrementally establish a consensus on the fundamental principles that underpin the use of DSLs, and to improve DSL tool interoperability

A minimal no-radiation approximation to Einstein's field equations

An approximation to Einstein's field equations in Arnowitt-Deser-Misner (ADM) canonical formalism is presented which corresponds to the magneto-hydrodynamics (MHD) approximation in electrodynamics. It results in coupled elliptic equations which represent the maximum of elliptic-type structure of Einstein's theory and naturally generalizes previous conformal-flat truncations of the theory. The Hamiltonian, in this approximation, is identical with the non-dissipative part of the Einsteinian one through the third post-Newtonian order. The proposed scheme, where stationary spacetimes are exactly reproduced, should be useful to construct {\em realistic} initial data for general relativistic simulations as well as to model astrophysical scenarios, where gravitational radiation reaction can be neglected.Comment: 9 page

Development of Uniform CdTe Pixel Detectors Based on Caltech ASIC

We have developed a large CdTe pixel detector with dimensions of 23.7 x 13.0 mm and a pixel size of 448 x 448 um^2. The detector is based on recent technologies of an uniform CdTe single crystal, a two-dimensional ASIC, and stud bump-bonding to connect pixel electrodes on the CdTe surface to the ASIC. Good spectra are obtained from 1051 pixels out of total 1056 pixels. When we operate the detector at -50 C, the energy resolution is 0.67 keV and 0.99 keV at 14 keV and 60 keV, respectively. Week-long stability of the detector is confirmed at operating temperatures of both -50 C and -20 C. The detector also shows high uniformity: the peak positions for all pixels agree to within 0.82%, and the average of the energy resolution is 1.04 keV at a temperature of -50 C. When we normalized the peak area by the total counts detected by each pixel, a variation of 2.1 % is obtained.Comment: 11pages, 17figures, accepted for publication in Proc. SPIE 200