To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Advances in scientific computing have made modelling and simulation an important part of the decision-making process in engineering, science, and public policy. This book provides a comprehensive and systematic development of the basic concepts, principles, and procedures for verification and validation of models and simulations. The emphasis is placed on models that are described by partial differential and integral equations and the simulations that result from their numerical solution. The methods described can be applied to a wide range of technical fields, from the physical sciences, engineering and technology and industry, through to environmental regulations and safety, product and plant safety, financial investing, and governmental regulations. This book will be genuinely welcomed by researchers, practitioners, and decision makers in a broad range of fields, who seek to improve the credibility and reliability of simulation results. It will also be appropriate either for university courses or for independent study.

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Verification and Validation in Scientific Computing

Laboratory-based courses play a critical role in scientific education. Automation is changing the nature of these laboratories, and there is a long-running debate about the value of hands-on versus simulated laboratories. In addition, the introduction of remote laboratories adds a third category to the debate. Through a review of the literature related to these labs in education, the authors draw several conclusions about the state of current research. The debate over different technologies is confounded by the use of different educational objectives as criteria for judging the laboratories: Hands-on advocates emphasize design skills, while remote lab advocates focus on conceptual understanding. We observe that the boundaries among the three labs are blurred in the sense that most laboratories are mediated by computers, and that the psychology of presence may be as important as technology. We also discuss areas for future research.

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Hands-on, simulated, and remote laboratories: A comparative literature review

The purpose of this research review is to open dialog about quantitative, qualitative, and mixed research methods in engineering education research. Our position is that no particular method is privileged over any other. Rather, the choice must be driven by the research questions. For each approach we offer a definition, aims, appropriate research questions, evaluation criteria, and examples from the Journal of Engineering Education. Then, we present empirical results from a prestigious international conference on engineering education research. Participants expressed disappointment in the low representation of qualitative studies; nonetheless, there appeared to be a strong preference for quantitative methods, particularly classroom-based experiments. Given the wide variety of issues still to be explored within engineering education, we expect that quantitative, qualitative, and mixed approaches will be essential in the future. We encourage readers to further investigate alternate research methods by accessing some of our sources and collaborating across education/social science and engineering disciplinary boundaries.

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Quantitative, Qualitative, and Mixed Research Methods in Engineering Education

The primary objective of this work is to provide accurate numerical solutions for selected flow fields and to compare and evaluate the performance of selected turbulence models with experimental results. Four popular turbulence models have been tested and validated against experimental data often turbulent flows. The models are: (1) the two-equation k-epsilon model of Wilcox, (2) the two-equation k-epsilon model of Launder and Sharma, (3) the two-equation k-omega/k-epsilon SST model of Menter, and (4) the one-equation model of Spalart and Allmaras. The flows investigated are five free shear flows consisting of a mixing layer, a round jet, a plane jet, a plane wake, and a compressible mixing layer; and five boundary layer flows consisting of an incompressible flat plate, a Mach 5 adiabatic flat plate, a separated boundary layer, an axisymmetric shock-wave/boundary layer interaction, and an RAE 2822 transonic airfoil. The experimental data for these flows are well established and have been extensively used in model developments. The results are shown in the following four sections: Part A describes the equations of motion and boundary conditions; Part B describes the model equations, constants, parameters, boundary conditions, and numerical implementation; and Parts C and D describe the experimental data and the performance of the models in the free-shear flows and the boundary layer flows, respectively.

Turbulence Modeling Validation, Testing, and Development

A high Reynolds number two-dimensional constant pressure compressible shear layer was formed at the trailing edge of an 0.5 mm-thick splitter plate. Convective Mach numbers of 0.51 and 0.64 were investigated using a two-component coincident LDV for the measurements. For the lower convective Mach number case, the nondimensionalized shear-layer and vorticity thickness growth rates were over 20 percent higher and the momentum thickness growth rate was over 30 percent higher than those of the higher convective Mach number case. The results seen to indicate that both small scale and large scale mixing are reduced with increasing convective Mach number.

Effects of compressibility on the characteristics of free shear layers

High-Reynolds-number compressible free shear layers were studied experimentally to explore the effects of compressibility on the turbulence field. A reduction in both the level and the lateral extent of turbulence fluctuations with increasing convective Mach number (Mc) (reported earlier for Mc of 0.51 and 0.64) is much higher at Mc of 0.86. The higher-order moments of turbulence fluctuations such as skewness and flatness show that the intermittency due to the excursion of large-scale structures into the free streams at the edge of shear layers was significantly reduced (both in the level and the extent) due to increased Mc.

Compressibility effects in free shear layers

An experimental investigation was conducted to examine the effect of a pulsed Nd:YAG laser energy addition on the shock structures and surface pressure in a Mach 3.45 flow past a sphere. Two configurations were considered: 1) a sphere in a uniform freestream and 2) an Edney IV interaction generated by impingement of an oblique shock on the bow shock of the sphere

Control of edney IV interaction by pulsed laser energy deposition

Increasingly mechanical engineering departments are beginning to incorporate remotely operated laboratories into their laboratory curriculums. Yet very few studies exist detailing the extent to which this new medium for laboratory delivery fulfills the educational goals of traditional in-person laboratories. This paper describes a comparison of educational outcomes between in-person and remotely operated laboratories in the mechanical engineering curriculum. The study carried out in the 2001 Fall semester was performed using a remotely operated and an in-person jet thrust laboratory. The laboratories illustrate the fundamentals of compressible fluid mechanics as part of an undergraduate mechanical engineering curriculum. The results from this study indicated no significant difference in the educational outcomes between students who performed the in-person or the remote experiment.

An Assessment of In‐Person and Remotely Operated Laboratories

Experiments were conducted to quantify the temperature and electron number density of a laser spark formed in air. The laser spark was created by focusing a 180-mJ beam from the second harmonic (wavelength of 532 nm) of a pulsed Nd:YAG laser with a 100-mm focal length lens. For early times, between 50 ns and 1 μs, images of the spark emission have been obtained to characterize the geometry. Also the temperature and electron number density were measured from the emission spectra between 490 and 520 nm where 46 N II lines are observed. The methodology of fitting the experimental data to the modeled spectra to deduce the temperature and electron number density is described. For the initial temporal range, the temperature peaks at approximately 50,000 K and decays over the first 1 μs. The electron number density peaks at approximately 10 19 cm -3 , decaying only slightly slower than t -1 . For the longer temporal evolution, from 20 to 1000 μs, planar temperature measurements were achieved using filtered Rayleigh scattering. The peak temperature starts at approximately 4100 K at 20 μs and decays to 580 K by 1 ms. The planar temperature images show a center jet propagating in the opposite direction as the initiating laser beam, which induces a vortex ring (or torus) propagating in the direction of the beam. The evolution of the position and radius of the torus structure is described and fit with a power law utilized by previous investigators. The temperature of the plasma created by laser-induced optical breakdown appears to fit quite well using a triple exponential over the four orders of magnitude of temporal range where measurements were conducted.

Gregory S. Elliott

Papers

Effects of compressibility on the characteristics of free shear layers

Compressibility effects in free shear layers

Control of edney IV interaction by pulsed laser energy deposition

An Assessment of In‐Person and Remotely Operated Laboratories

Temporal and Spatial Evolution of a Laser Spark in Air