43,480 research outputs found
Flow-Control Effectiveness of Convergent Surface Indentations on an Aerofoil at Low Reynolds Numbers
Passive flow control on aerofoils has largely been achieved through the use of protrusions
such as vane-type vortex generators. Consequently, innovative flow-control concepts should
be explored in an effort to improve current component performance. Therefore,
experimental research has been performed at The University of Manchester to evaluate the
flow-control effectiveness of a novel type of vortex generator made in the form of a surface
indentation. The surface indentation has a trapezoidal planform. A spanwise array of
indentations has been applied in a convergent orientation around the maximum-thickness
location of the upper surface of a NACA-0015 aerofoil. The aerofoil has been tested in a twodimensional
set-up in a low-speed wind tunnel at an angle of attack (AoA) of 3° and a chordbased
blockage-corrected Reynolds number (Recorr) of ~2.70 x 105
. The baseline model has
been found to suffer from a long laminar separation bubble (LSB) at low AoA. The
application of the indentations at low AoA has considerably shortened the separation
bubble. The indentations achieve this by shedding up-flow pairs of streamwise vortices.
Despite the considerable reduction in bubble length, the increase in leading-edge suction due
to the shorter bubble is limited by the removal of surface curvature and blockage (increase
in surface pressure) caused locally by the convergent indentations. Furthermore, the up-flow
region of the vortices, which locally weakens the pressure recovery around the trailing edge
of the aerofoil by thickening the boundary layer, also contributes to this limitation. Due to
the conflicting effects of the indentations, the changes in the pressure-lift and pressure-drag
coefficients, i.e., cl,p and cd,p, respectively, are small. Nevertheless, the indentations have
improved cl,p and cd,p beyond the uncertainty range, i.e., by ~1.3% and ~0.3%, respectively,
at 3° AoA. The wake measurements show that turbulence intensity and Reynolds stresses
have considerably increased in the indented case, thus implying that the indentations
increase the viscous drag on the model. In summary, the convergent indentations are able to
reduce the size of the LSB, but conversely, they are not highly effective in enhancing cl,p and
cd,p at the tested Re
Hydrogen transport in alpha titanium
Permeation experiments after nitriding the inlet surface of a hollow cylindrical membrane were conducted. Permeation data on two additional specimens given pre-oxidation or pre-nitriding treatments at both inlet and outlet surfaces are presented in terms of Arrhenius plots. Additionally, an analysis of geometry dependence on permeation rate was made for several specimens including the ones mentioned above. For simplicity in this report, the term as-polished is used to refer to a specimen which is either as-polished or is as-polished, pre-oxidized and annealed
Design Architecture-Based on Web Server and Application Cluster in Cloud Environment
Cloud has been a computational and storage solution for many data centric
organizations. The problem today those organizations are facing from the cloud
is in data searching in an efficient manner. A framework is required to
distribute the work of searching and fetching from thousands of computers. The
data in HDFS is scattered and needs lots of time to retrieve. The major idea is
to design a web server in the map phase using the jetty web server which will
give a fast and efficient way of searching data in MapReduce paradigm. For real
time processing on Hadoop, a searchable mechanism is implemented in HDFS by
creating a multilevel index in web server with multi-level index keys. The web
server uses to handle traffic throughput. By web clustering technology we can
improve the application performance. To keep the work down, the load balancer
should automatically be able to distribute load to the newly added nodes in the
server
Mathematical modelling of the catalyst layer of a polymer-electrolyte fuel cell
In this paper we derive a mathematical model for the cathode catalyst layer of a polymer electrolyte fuel cell. The model explicitly incorporates the restriction placed on oxygen in reaching the reaction sites, capturing the experimentally observed fall in the current density to a limiting value at low cell voltages. Temperature variations and interfacial transfer of O2 between the dissolved and gas phases are also included. Bounds on the solutions are derived, from which we provide a rigorous proof that the model admits a solution. Of particular interest are the maximum and minimum attainable values. We perform an asymptotic analysis in several limits inherent in the problem by identifying important groupings of parameters. This analysis reveals a number of key relationships between the solutions, including the current density, and the composition of the layer. A comparison of numerically computed and asymptotic solutions shows very good agreement. Implications of the results are discussed and future work is outlined
- …