Development and Test Results of a Multi-Evaporator-Condensor Loop Heat Pipe

This technical report (NLR-TP-2002-491) was published by NLR (the National Aerospace Laboratory of the Netherlands) in 2002 and was written by A. A. M. Delil, Y. F. Maydanik, M. A. Chernyshova and V. G. Pasthukhov. Results are presented of the development and tests of a 1 m long ammonia ramified loop heat pipe, with two cylindrical evaporators (24 mm in diameter with an active zone length of 150 mm) and two condensers (length 200 mm, diameter 24 mm), made as pipe-in-pipe heat exchangers. Tests of the device at different orientations in 1-g have shown that it can efficiently operate at symmetrical and non-symmetrical heat load distributions between the evaporators, and also at different temperatures of the condensers cooling. The maximum total transport capacity is 1100-1400 W. Shutting down the active cooling of one condenser results in an abrupt decrease in the maximum transport capability of the device. [Taken from abstract]. The full text is available as a PDF file.

Distribution Iteration: A Robust Alternative to Source Iteration for Solving the Discrete Ordinates Radiation Transport Equations in Slab and XY - Geometries

This is the full text of a thesis written by Nicholas Prins which was presented to the Air Force Institute of Technology, Wright Patterson Air Force Base, Ohio, in September 2008. The discrete ordinates method is widely used to solve the Boltzmann transport equation for neutral particle transport for many engineering applications. Source iteration is used to solve the discrete ordinates system of equations, but can be slow to converge in highly scattering problems. Synthetic acceleration techniques have been developed to address this shortcoming; however, recent research has shown synthetic acceleration to lose effectiveness or diverge for certain problems. LTC Wager introduced an alternative to source iteration and demonstrated it in slab geometry. Here the method is further developed, enhancing efficiency in various ways, and demonstrated in XY-geometry as well as slab geometry. It is shown to be efficient even for those problems for which diffusion-synthetic and transport-synthetic accelerations fail or are ineffective. The method has significant advantages for massively-parallel implementations. [Taken from Abstract]. This is in PDF format so Adobe Acrobat software is required in order to read it.

Effects of High Intensity, Large-Scale Freestream Combustor Turbulence On Heat Transfer in Transonic Turbine Blades

This is a Virginia Polytechnic Institute and State University Department of Mechanical Engineering PhD dissertation, by Andrew Carl Nix, dated April, 2003. The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. Measurements were performed on a high turning, transonic turbine blade. An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations (u'RMS) and length-scale (Lx). The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane and turbine blade) as well as both laminar and turbulent boundary layers, but demonstrated limitations in predicting early transition and heat transfer in turbulent boundary layers. Bibliographic and abstract details are available in HTML format. The full text of the document is accessible online in PDF format [9.35 Mb]. This title is part of Virginia Tech’s Electronic Thesis and Dissertation Collection (VT ETD).

Heat Transfer and Cooling in Gas Turbines

This is Research and Technology Organization (RTO) AGARD-CP-527, dated February 1993. The symposium was arranged in the following sessions: turbine blades--external heat transfer; turbine blades--internal heat transfer; measurement techniques; rotating disks, labyrinth seals, and shafts; combustors; design, interactions; and prediction methods. Heat transfer and cooling in gas turbines are still key factors for achieving high performance, increased life, and improved reliability. Any progress in this field will lead to a reduction of maintenance cost and fuel consumption. The purpose of the symposium was to bring together experts from industry, research establishments, and universities to discuss fundamental and applied heat transfer problems relevant to gas turbines, to exchange practical experience gained, and to review the state of the art. For individual titles, see N93-29927 through N93-29964. Bibliographic and abstract details are available in HTML format. A table of contents, and the full text (156.97MB) of the document can be accessed online in PDF format. The document is contained in the RTO's Full Text Publication Library.

Heat-transfer measurements in short-duration hypersonic facilities

This is Research and Technology Organization (RTO) AGARD-AG-165, dated February 1973. The techniques for making measurements of heat transfer in short duration and rapidly varying flows are reviewed. Methods discussed include: gauges operating on the semi-infinite principle, calorimeter gauges, pyroelectric heat transfer gauges, measurement of radiative heat transfer, and optical methods. The error in deduced heat transfer rate arising from a surface temperature discontinuity due to the presence of an isolated heat transfer gauge is also discussed. Bibliographic and abstract details are available in HTML format. A table of contents, and the full text (4.42MB) of the document can be accessed online in PDF format. The document is contained in the RTO's Full Text Publication Library.

High temperature turbines

This is Research and Technology Organization (RTO) AGARD-AR-29, dated February 1971. The 36th meeting of the Propulsion and Energetics Panel of the NATO Advisory Group for Aerospace Research and Development was held at the Scuola di Guerra Aerea in Florence, Italy from 21 to 25 September, 1970. The program, which was arranged by a committee under the Chairmanship of Ing. Principal M. Pianko, was devoted to the subject of high temperature turbines. There is a continuing demand by the aircraft designer for engines that weigh less and, at the same time provide more thrust , the maximum cycle temperature at which aircraft gas turbines are designed to operate is increasing as rapidly as the technology of high temperature materials and blade cooling will allow. Practically all types of aircraft gas turbines are now designed for turbine inlet temperatures such that turbine blade cooling is an absolute requirement. The balance of the subject matter covered by the papers given at the meeting was reasonably good. The first paper of the meeting by Alesi set the stage for those that followed by reviewing the improvements in cycle performance that can be obtained by going t o higher turbine i n l e t temperatures. The remaining papers, which were organized in such a way as t o provide a degree of variety, covered the following topics : 1. A review of the factors affecting the heat transfer processes involved in convection, film and transpiration cooling and an evaluation of the effectiveness of these cooling techniques 2. The problems involved in cooling small turbines 3. The practical problems involved in the application of turbine blade cooling to engines 4. Metallurgical problems t o be considered in the selection of high temperature and cooled turbine materials 5. Heat transfer measurement techniques Bibliographic and abstract details are available in HTML format. A table of contents and the full text (681KB) of the document can be accessed online in PDF format. The document is contained in the RTO's Full Text Publication Library.

High temperature turbines

This is Research and Technology Organization (RTO) AGARD-CP-73, dated January 1971. In the earlier years of development, metallurgical advances of themselves made it possible to raise turbine operating temperatures from the region of 7OOC to around 1000. During the last decade, an important step forward was achieved with the introduction of the use of cooled turbine blades. Today, turbine engines are under development and in use which incorporate cooled blades operating at temperatures of about 115OC. Considerable effort is continuing in the investigation of new and improved materials and of more advanced blade cooling methods, with the aim of raising operating temperatures up to and beyond 13OOC. The purpose of this meeting is to review and highlight the main aspects of the problems of achieving high temperatures in aeronautical turbines, problems whose resolution will lead to overall improvements in the performances of turbine engines and open up wider fields for their utilization. Bibliographic and abstract details are available in HTML format. A table of contents and the full text (114MB) of the document can be accessed online in PDF format. The document is contained in the RTO's Full Text Publication Library.

In-flight Temperature Measurements

This is Research and Technology Organization (RTO) AGARD-AG-160-02, dated February 1973. This AGARDograph of the AGARD Flight Test Instrumentation Series discusses temperature measurements in aircraft at Mach numbers up to 2.3 and altitudes up to 80,000 feet. The requirements of aircraft temperature measurements and the available temperature sensing technology are discussed and the detailed techniques of using resistance probes and thermocouples are explained. Heat transfer processes, primarily between moving fluids and solids, are discussed. An extensive section deals with errors in temperature measurements. Typical laboratory and in-flight calibration techniques for thermometers are described, followed by discussions of data handling, error analysis, and the limits of present methods. Bibliographic and abstract details are available in HTML format. A table of contents, and the full text (216KB) of the document can be accessed online in PDF format. The document is contained in the RTO's Full Text Publication Library.

Local Search Methods for Design in Aeronautics

The material in this publication was assembled to support a Lecture Series under the sponsorship of the Applied Vehicle Technology Panel (AVT) and the Consultant and Exchange Programme of RTA presented on 9-10 September 2010 in Berlin, Germany. Published September 2010

Numerical optimisation aims at locating the minima of a regular function (called objective function) on a finite-dimensional design space, while satisfying a certain number of constraints (expressed as inequality verified by the so-called constraint functions). More precisely, local optimisation aims at finding a local optimum in the neighborhood of an initial guess, whereas global optimisation aims at finding the global optimum on the whole design space. These problems are, of course, the mathematical counterparts of mechanical optimisation problems - like drag minimisation of an aircraft or total pressure maximisation of a supersonic aircraft air intake - as soon as (a) a mesh and a simulation tool are available ; (b) the solid shape has been parameterised/a remeshing tool is available to propagate its deformation to the whole mesh ; (c) the objective and constraints have been expressed as functions of the geometry and state variables.

Numerical optimisation for airplane design was used almost as soon as simulation codes appeared. The aerodynamic optimisations carried out by G.N. Van der Plaats at NASA in the mid 70’s illustrate this early interest in optimisation [1]. At that time, 2D and simple 3D configurations were considered, simplex or descent methods were used and the gradients required by descent methods were estimated by the finite-differences. Since then, the framework of aerospace optimisation has known at least three drastic extensions:

1. (1) several global optimisation methods have been defined and intensively used (evolutionary algorithm, particle swarm, ant colony, simulated annealing,...);
2. (2) surrogate functions (neural network, Kriging, polynomial regression, support vector machine,...) have been used for a part of the evaluation of the global optimisation methods leading to significant cost reductions;
3. (3) adjoint vector and direct differentiation method have been defined , studied and more and more often used to computate the gradients necessary for descent algorithms.