107 research outputs found
Propagation of gaseous detonation waves in a spatially inhomogeneous reactive medium
Detonation propagation in a compressible medium wherein the energy release
has been made spatially inhomogeneous is examined via numerical simulation. The
inhomogeneity is introduced via step functions in the reaction progress
variable, with the local value of energy release correspondingly increased so
as to maintain the same average energy density in the medium, and thus a
constant Chapman Jouguet (CJ) detonation velocity. A one-step Arrhenius rate
governs the rate of energy release in the reactive zones. The resulting
dynamics of a detonation propagating in such systems with one-dimensional
layers and two-dimensional squares are simulated using a Godunov-type
finite-volume scheme. The resulting wave dynamics are analyzed by computing the
average wave velocity and one-dimensional averaged wave structure. In the case
of sufficiently inhomogeneous media wherein the spacing between reactive zones
is greater than the inherent reaction zone length, average wave speeds
significantly greater than the corresponding CJ speed of the homogenized medium
are obtained. If the shock transit time between reactive zones is less than the
reaction time scale, then the classical CJ detonation velocity is recovered.
The spatio-temporal averaged structure of the waves in these systems is
analyzed via a Favre averaging technique, with terms associated with the
thermal and mechanical fluctuations being explicitly computed. The analysis of
the averaged wave structure identifies the super-CJ detonations as weak
detonations owing to the existence of mechanical non-equilibrium at the
effective sonic point embedded within the wave structure. The correspondence of
the super-CJ behavior identified in this study with real detonation phenomena
that may be observed in experiments is discussed
Design and Analysis: Servo-Tube-Powered Liquid Jet Injector for Drug Delivery Applications
The current state of commercially available needle-free liquid jet injectors for drug delivery offers no way of controlling the output pressure of the device in real time, as the driving mechanism for these injectors provides a fixed delivery pressure profile. In order to improve the delivery efficiency as well as the precision of the targeted tissue depth, it is necessary to develop a power source that can accurately control the plunger velocity. The duration of a liquid jet injection can vary from 10 to 100 ms, and it generate acceleration greater than 2 g (where g is the gravity); thus, a platform for real-time control must exhibit a response time greater than 1 kHz and good accuracy. Improving the pioneering work by Taberner and others whereby a Lorentz force actuator based upon a voice coil is designed, this study presents a prototype injector system with greater controllability based on the use of a fully closed-loop control system and a classical three-phase linear motor consisting of three fixed coils and multiple permanent magnets. Apart from being capable of generating jets with a required stagnation pressure of 15–16 MPa for skin penetration and liquid injection, as well as reproducing typical injection dynamics using commercially available injectors, the novelty of this proposed platform is that it is proven to be capable of shaping the real-time jet injection pressure profile, including pulsed injection, so that it can later be tailored for more efficient drug delivery
Design analysis and comparison between standard and rotary porting systems for IC engine
Many porting systems for internal combustion engines have been tried and tested over the years, however the basic spring actuated poppet valve system has prevailed over the last century. In the goal to lower engine output parasitic losses, a simple rotary valve porting system design is proposed and analyzed. The proposed design concept takes into consideration and combines all the prominent advantages of many ealier mutlitiple design variations over the past century. The inherent primary advantage of such a rotary porting system is the elimination of reciprocating components, thus lowering vibration, and removal of highly stiff springs which contribute to considerable system power loss. Comparable sized 3-D representations of both systems are constructed in CAD (Computer Aided Design) software in order to run mechanical and fluid simulations to validate the efficiency advantage of a rotary valve porting system. Using Pro/Engineer Mechanism Dynamics module, the minimum torque required to actuate both systems at 2000 rpm and 3000 rpm is determined. Fluid simulations are performed using a commercial software CFDesign V10. Volumetric flow rates are compared during the intake stroke as well as turbulence intensity factors which characterizes a systems ability to properly mix the Air/Fuel mixture and the combustion efficiency. Some possible improvement on the rotary geometry is suggested
An experimental investigation of the explosion characteristics of dimethyl ether-air mixtures
Mixing Within Patterned Vortex Core
The video shows the flow dynamics within inner and outer regions of a vortex
core. The observed phenomena mimic a transport process occurring within the
Antarctic vortex. The video shows two distinct regions: a strongly mixed core
and broad ring of weakly mixed region extending out the vortex core boundaries.
The two regions are separated by a thin layer that isolates the weakly and
strongly mixed regions; this thin layer behaves as barrier to the mixing of the
two regions. The video shows that the barriers deplete when a swirl of the
vortex core increases and the vortex core espouses a triangular pattern.Comment: 62nd Annual Meeting of the APS Division of Fluid Dynamics, Fluid
Dynamics Vide
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