An Experimental Study of Spark Anemometry for In-Cylinder Velocity Measurements

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
D. P. Gardiner ◽  
G. Wang ◽  
M. F. Bardon ◽  
M. LaViolette ◽  
W. D. Allan
Keyword(s):  
Experimental Study ◽  
Flow Velocity ◽  
High Speed ◽  
Spark Ignition Engine ◽  
Constant Current ◽  
Velocity Measurements ◽  
Lower Velocity ◽  
Freestream Velocity ◽  
Channel Shape ◽  
Spark Channel

It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current wave forms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. While earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high-speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the freestream gas velocity. A lower velocity threshold exists below, which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the freestream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.

An Experimental Study of Spark Anemometry for In-Cylinder Velocity Measurements

2006 ◽  
Author(s):  
D. P. Gardiner ◽  
G. Wang ◽  
M. F. Bardon ◽  
M. LaViolette ◽  
W. D. Allan
Keyword(s):  
Experimental Study ◽  
Flow Velocity ◽  
Free Stream ◽  
Spark Ignition Engine ◽  
Constant Current ◽  
Stream Velocity ◽  
Velocity Measurements ◽  
Lower Velocity ◽  
Channel Shape ◽  
Spark Channel

It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current waveforms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. Whereas earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the free stream gas velocity. A lower velocity threshold exists below which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the free stream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.

Cavitation about a jet in crossflow

2015 ◽  
Vol 768 ◽  
pp. 141-174 ◽  
Author(s):  
P. A. Brandner ◽  
B. W. Pearce ◽  
K. L. de Graaf
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
High Speed ◽  
Velocity Ratio ◽  
Cavitation Number ◽  
Variable Pressure ◽  
Lower Velocity ◽  
Freestream Velocity ◽  
Jet In Crossflow ◽  
Cavity Closure

Cavitation occurrence about a jet in crossflow is investigated experimentally in a variable-pressure water tunnel using still and high-speed photography. The 0.012 m diameter jet is injected on the centreplane of a 0.6 m square test section at jet to freestream velocity ratios ranging from 0.2 to 1.6, corresponding to jet-velocity-based Reynolds numbers of $25\times 10^{3}$ to $160\times 10^{3}$ respectively. Measurements were made at a fixed freestream-based Reynolds number, for which the ratio of the undisturbed boundary layer thickness to jet diameter is 1.18. The cavitation number was varied from inception (up to about 10) down to 0.1. Inception is investigated acoustically for bounding cases of high and low susceptibility to phase change. The influence of velocity ratio and cavitation number on cavity topology and geometry are quantified from the photography. High-speed photographic recordings made at 6 kHz provide insight into cavity dynamics, and derived time series of spatially averaged pixel intensities enable frequency analysis of coherent phenomena. Cavitation inception was found to occur in the high-shear regions either side of the exiting jet and to be of an intermittent nature, increasing in occurrence and duration from 0 to 100 % probability with decreasing cavitation number or increasing jet to freestream velocity ratio. The frequency and duration of individual events strongly depends on the cavitation nuclei supply within the approaching boundary layer. Macroscopic cavitation develops downstream of the jet with reduction of the cavitation number beyond inception, the length of which has a power-law dependence on the cavitation number and a linear dependence on the jet to freestream velocity ratio. The cavity closure develops a re-entrant jet with increase in length forming a standing wave within the cavity. For sufficiently low cavitation numbers the projection of the re-entrant jet fluid no longer reaches the cavity leading edge, analogous to supercavitation forming about solid cavitators. Hairpin-shaped vortices are coherently shed from the cavity closure via mechanisms of shear-layer roll-up similar to those shed from protuberances and jets in crossflow in single-phase flows. These vortices are shed at an apparently constant frequency, independent of the jet to freestream velocity ratio but decreasing in frequency with reducing cavitation number and cavity volume growth. Highly coherent cavitating vortices form along the leading part of the cavity due to instability of the jet upstream shear layer for jet to freestream velocity ratios greater than about 0.8. These vortices are cancelled and condense as they approach the trailing edge in the shear layer of opposing vorticity associated with the cavity closure and the hairpin vortex formation. For lower velocity ratios, where there is decreased jet penetration, the jet upstream shear velocity gradient reverses and vortices of the opposite sense form, randomly modulated by boundary layer turbulence.

Shock Wave and Flow Velocity Measurements in a High Speed Fan Rotor Using the Laser Velocimeter

1977 ◽  
Vol 99 (2) ◽  
pp. 181-187 ◽  
Author(s):  
D. C. Wisler
Keyword(s):  
Shock Wave ◽  
Flow Velocity ◽  
High Speed ◽  
Fluid Dynamic ◽  
Equations Of Motion ◽  
Seed Particle ◽  
Gas Velocity ◽  
Velocity Measurements ◽  
Rotating Blade ◽  
Finite Difference Solution

The laser velocimeter, an instrument capable of making nondisturbing gas velocity measurements, was used to determine shock wave locations and to make gas velocity measurements within the rotating blade row of a 550-m/s (1800-ft/s)-tip speed fan rotor. The velocimeter measures the transit time of a seed particle across interference fringes produced at the intersection of a split and crossed laser beam. The rotor flowfields were obtained at several radial immersions for operating-line and near-stall throttle settings. The results show the change in shock pattern and flow velocity as the compressor is throttled toward stall. Analytical predictions of the flowfield were also obtained using both the method of characteristics and a time-dependent, finite-difference solution of the fluid dynamic equations of motion. The analytical results and the flowfield measurements are considered to be in good agreement.

Some Special Aspects of Hypersonic Flow Fields

1959 ◽  
Vol 63 (585) ◽  
pp. 508-512 ◽  
Author(s):  
K. W. Mangler
Keyword(s):  
Hypersonic Flow ◽  
High Speed ◽  
Flow Fields ◽  
The Body ◽  
Lower Velocity ◽  
Bow Wave ◽  
Total Head ◽  
Bow Shocks ◽  
Lower Entropy ◽  
Subsonic Region

When a body moves through air at very high speed at such a height that the air can be considered as a continuum, the distinction between sharp and blunt noses with their attached or detached bow shocks loses its significance, since, in practical cases, the bow wave is always detached and fairly strong. In practice, all bodies behave as blunt shapes with a smaller or larger subsonic region near the nose where the entropy and the corresponding loss of total head change from streamline to streamline due to the curvature of the bow shock. These entropy gradients determine the behaviour of the hypersonic flow fields to a large extent. Even in regions where viscosity effects are small they give rise to gradients of the velocity and shear layers with a lower velocity and a higher entropy near the surface than would occur in their absence. Thus one can expect to gain some relief in the heating problems arising on the surface of the body. On the other hand, one would lose farther downstream on long slender shapes as more and more air of lower entropy is entrained into the boundary layer so that the heat transfer to the surface goes up again. Both these flow regions will be discussed here for the simple case of a body of axial symmetry at zero incidence. Finally, some remarks on the flow field past a lifting body will be made. Recently, a great deal of information on these subjects has appeared in a number of reviewing papers so that little can be added. The numerical results on the subsonic flow regions in Section 2 have not been published before.

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