803 research outputs found
Turbine vane gas film cooling with injection in the leading edge region from a single row of spanwise angled holes
An experimental study of gas film cooling was conducted on a 3X size model turbine vane. Injection in the leading edge region was from a single row of holes angled in a spanwise direction. Measurements of the local heat flux downstream from the row of coolant holes, both with and without film coolant flow, were used to determine the film cooling performance presented in terms of the Stanton number ratio. Results for a range of coolant blowing ratio, M = 0 to 2.0, indicate a reduction in heat flux of up to 15 to 30 percent at a point 10 to 11 hole diameters downstream from injection. An optimum coolant blowing ratio corresponds to a coolant-to-freestream velocity ratio in the range of 0.5. The shallow injection angle resulted in superior cooling performance for injection closest to stagnation, while the effect of injection angle was insignificant for injection further from stagnation
Asteroid models from the Lowell Photometric Database
We use the lightcurve inversion method to derive new shape models and spin
states of asteroids from the sparse-in-time photometry compiled in the Lowell
Photometric Database. To speed up the time-consuming process of scanning the
period parameter space through the use of convex shape models, we use the
distributed computing project Asteroids@home, running on the Berkeley Open
Infrastructure for Network Computing (BOINC) platform. This way, the
period-search interval is divided into hundreds of smaller intervals. These
intervals are scanned separately by different volunteers and then joined
together. We also use an alternative, faster, approach when searching the
best-fit period by using a model of triaxial ellipsoid. By this, we can
independently confirm periods found with convex models and also find rotation
periods for some of those asteroids for which the convex-model approach gives
too many solutions. From the analysis of Lowell photometric data of the first
100,000 numbered asteroids, we derived 328 new models. This almost doubles the
number of available models. We tested the reliability of our results by
comparing models that were derived from purely Lowell data with those based on
dense lightcurves, and we found that the rate of false-positive solutions is
very low. We also present updated plots of the distribution of spin obliquities
and pole ecliptic longitudes that confirm previous findings about a non-uniform
distribution of spin axes. However, the models reconstructed from noisy sparse
data are heavily biased towards more elongated bodies with high lightcurve
amplitudes
An analytical and experimental study of heat transfer in a simulated Martian atmosphere Final report, 1 Nov. 1968 - 15 Oct. 1969
Convective heat transfer in simulated Martian atmospher
Composite Axial Flow Propulsor for Small Aircraft
This work focuses on the design of an axial flow ducted fan driven by a reciprocating engine. The solution minimizes the turbulization of the flow around the aircraft. The fan has a rotor - stator configuration. Due to the need for low weight of the fan, a carbon/epoxy composite material was chosen for the blades and the driving shaft.The fan is designed for optimal isentropic efficiency and free vortex flow. A stress analysis of the rotor blade was performed using the Finite Element Method. The skin of the blade is calculated as a laminate and the foam core as a solid. A static and dynamic analysis were made. The RTM technology is compared with other technologies and is described in detail.
Inlet Channel for a Ducted Fan Propulsion System of a Light Aircraft
So-called "cold-jet" propulsion units consist of a piston engine, a blower and the necessary air duct. Till now, all attempts to utilize "cold-jet" propulsion units to maintain the thrust of an airplane have been unsuccessful. Analysis has shown that the main difficulty is the deformation of the flow field at the entry to the blower [1]
Design of Carbon Composite Driveshaft for Ultralight Aircraft Propulsion System
This paper deals with the design of the carbon fibre composite driveshaft. This driveshaft will be used for connection between piston engine and propulsor of the type of axial-flow fan. Three different versions of driveshaft were designed and produced. Version 1 if completely made of Al alloy. Version 2 is of hybrid design where the central part is made of high strength carbon composite and flanges are made of Al alloy. Adhesive bond is used for connection between flanges and the central CFRP tube. Version 3 differs from the version 2 by aplication of ultrahigh-strength carbon fibre on the central part. Dimensions and design conditions are equal for all three versions to obtain simply comparable results. Calculations of driveshafts are described in the paper.
Combining Static and Dynamic Contract Checking for Curry
Static type systems are usually not sufficient to express all requirements on
function calls. Hence, contracts with pre- and postconditions can be used to
express more complex constraints on operations. Contracts can be checked at run
time to ensure that operations are only invoked with reasonable arguments and
return intended results. Although such dynamic contract checking provides more
reliable program execution, it requires execution time and could lead to
program crashes that might be detected with more advanced methods at compile
time. To improve this situation for declarative languages, we present an
approach to combine static and dynamic contract checking for the functional
logic language Curry. Based on a formal model of contract checking for
functional logic programming, we propose an automatic method to verify
contracts at compile time. If a contract is successfully verified, dynamic
checking of it can be omitted. This method decreases execution time without
degrading reliable program execution. In the best case, when all contracts are
statically verified, it provides trust in the software since crashes due to
contract violations cannot occur during program execution.Comment: Pre-proceedings paper presented at the 27th International Symposium
on Logic-Based Program Synthesis and Transformation (LOPSTR 2017), Namur,
Belgium, 10-12 October 2017 (arXiv:1708.07854
Non-linear Pattern Matching with Backtracking for Non-free Data Types
Non-free data types are data types whose data have no canonical forms. For
example, multisets are non-free data types because the multiset has
two other equivalent but literally different forms and .
Pattern matching is known to provide a handy tool set to treat such data types.
Although many studies on pattern matching and implementations for practical
programming languages have been proposed so far, we observe that none of these
studies satisfy all the criteria of practical pattern matching, which are as
follows: i) efficiency of the backtracking algorithm for non-linear patterns,
ii) extensibility of matching process, and iii) polymorphism in patterns.
This paper aims to design a new pattern-matching-oriented programming
language that satisfies all the above three criteria. The proposed language
features clean Scheme-like syntax and efficient and extensible pattern matching
semantics. This programming language is especially useful for the processing of
complex non-free data types that not only include multisets and sets but also
graphs and symbolic mathematical expressions. We discuss the importance of our
criteria of practical pattern matching and how our language design naturally
arises from the criteria. The proposed language has been already implemented
and open-sourced as the Egison programming language
A 380 GHz SIS receiver using Nb/AlO(x)/Nb junctions for a radioastronomical balloon-borne experiment: PRONAOS
The superheterodyne detection technique used for the spectrometer instrument of the PRONAOS project will provide a very high spectral resolution (delta nu/nu = 10(exp -6)). The most critical components are those located at the front-end of the receiver: their contribution dominates the total noise of the receiver. Therefore, it is important to perform accurate studies for specific components, such as mixers and multipliers working in the submillimeter wave range. Difficulties in generating enough local oscillator (LO) power at high frequencies make SIS mixers very desirable for operation above 300 GHz. The low LO power requirements and the low noise temperature of these mixers are the primary reason for building an SIS receiver. This paper reports the successful fabrication of small (less than or equal to 1 sq micron) Nb/Al-O(x)/Nb junctions and arrays with excellent I-V characteristics and very good reliability, resulting in a low noise receiver performance measured in the 368/380 GHz frequency range
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