Initial Jet Velocity Research Articles

上底吹き転炉における二次燃焼技術の開発

A post combustion (P·C) nozzle which accomplishes high P·C and heat transfer efficiency in a converter was developed through studies of both nozzle profile for maintaining stable P·C and appropriate P·C regin. By applying the abrupt expansion P·C nozzle to the 180t LD-KGC converters of Kawasaki Steel Corp., the following results were obtained. 1) In order to enhance heat transfer to molten steel, it is desirable to form the P·C region in a space near the molten steel surface and approximately more than 1.0 m inside the furnace wall refractories. 2) It is estimated that the P·C nozzle forms diffusion combustion due to the collision between oxygen jet and carbon monoxide gas. Therefore the oxygen flow velocity into the combustion region should be controlled under 10 m/s. For this purpose, it is required to keep the initial jet velocity from the nozzle within 100 m/s. 3) The P·C ratio increases with the lance height but the heat transfer ratio is almost constant at 60% regardless of the lance height. 4) The scrap ratio increased by 6% when P·C oxygen of 0.5 Nm3/min·t is supplied. 5) The developed abrupt expansion P·C nozzle has no significant effects on metallurgical reactions, and the values of (T-Fe) and (P)/ [P] are almost the same as those in the conventional process.

Normal impingement of an axisymmetric turbulent air jet. Experiments.

In order to clarify the flow characteristics of a circular turbulent air jet impinging normally onto a fiat surface, the distributions of jet velocity and its turbulence intensity in the impingement region of the jet were measured in detail by hot-wire anemometry by changing the jet nozzle diameter, initial jet velocity and impinging height etc.. Consequently, those measurements were found to be similar to the velocity distribution in the free or wall jet region respectively, and also showed a reasonable agreement with the results calculated numerically assuming a new velocity distribution on the inflow boundary line of the impingement region.

Ignition and combustion mechanism in a prechamber combustor (Quantitative classification of combustion patterns)

Effects of the volume ratio, nozzle diameter, and the surface to volume ratio of the nozzle (S/V-value) on the initial jet velocity and ignition induction period are experimentally investigated in order to obtain a clear picture of the interrelation between the jet region in the main chamber at the very ignition and the combustion pattern. a reduction of the S/V-value under a constant nozzle diameter increases the initial jet velocity, leaving the ignition induction period almost unvaried. The higher the jet velocity and the longer the induction period, the greater the jet region and the lower the mean temperature within the region, resulting in an extremely rapid combustion in the main chamber. The combustion pattern parameter, derived from the dimensional analysis and defined by X=ujτi/d, is found to be a simple measure to classify quantitatively the ignition and combustion processes in the main chamber independently of the volume ratio, nozzle diameter, and the S/V-value.

Density effects on jet characteristics in confined swirling flow

Density effects on isothermal jet mixing in confined swirling flow are investigated. The experiment is carried out with helium/air as the jet fluid in the same facility as that used by So et al. (1984a, b) and the test conditions are chosen to be the same as before. Contrary to the homogeneous mixing results, the helium jet is preserved up to 40 jet diameters downstream. The behavior of the mean and turbulence field depends highly on the initial jet velocity. Since the jets are fully turbulent and the jet momentum fluxes for inhomogeneous mixing are less than those for homogeneous mixing, the cause of this difference in behavior is directly attributed to the combined action of density difference and swirl. In spite of this, near isotropy of the turbulence field is again observed at ∼ 40 jet diameters downstream.

Ignition and burning process in a divided chamber bomb

Ignition and burning mechanisms of the main chamber mixture by a torch jet were experimentally investigated using a divided chamber bomb. The effects of the nozzle diameter and volume ratio on the structure of the torch jet, ignition process, and subsequent burning process in the main chamber were minutely examined, in both uniform and stratified charges, by measurements of ion current, light emission, OH-emission (306.4 nm), initial torch jet velocity, and main chamber pressure histories and by schlieren photography. The structure of the torch jet was greatly influenced by the nozzle diameter and volume ratio independently of the main chamber mixture ratio. According to the physical and chemical characteristics obtained for it, the structure of the torch jet could be classified into four types, and the ignition and burning processes in the main chamber could also be classified into four patterns depending on the torch jet structure: pattern I, chemical chain ignition and well-dispersed burning; pattern II, composite ignition and well-dispersed burning followed by wrinkled laminar burning; pattern III, flame kernel torch ignition and wrinkled laminar burning; and pattern IV, flame front torch ignition and wrinkled laminar burning. Combustion characteristics such as main chamber pressure and net burning time in the main chamber also showed their own peculiar features. Examination of the lean flammability limit gave a possibility of lean burning outside of the normal flammability limit by using divided chamber systems. From these results combustion pattern II was found to be most favorable for lean burning.

Optimization of shaped charges

Efficient design of shaped charges requires a full calculation of all three basic processes involved: liner collapse, jet fragmentation, and subsequent penetration in the target. Claims have been made [S. S. Grigoryan and N. S. Sanasaryan, Mekh. Zhidkosti Gaza 6, 9 (1974); N. S. Sanasaryan, ibid. 6, 151 (1975)] that for given standoff distance, a certain initial jet velocity profile exists that corresponds to maximum penetration at this distance. We demonstrate that no such profile exists. In fact, the velocity profile yielding maximum penetration depth corresponds to infinite strain and is therefore of no practical interest. We abandon the ‘‘moving tank’’ representation of the jet formation adopted by previous authors, and treat the initial axial profiles of jet velocity and strain rate as independent quantities that are intrinsically related only through the shaped charge design. A general relationship is derived between initial axial profiles of jet velocity, strain rate, and total strain for a jet fragmenting exactly in the bottom of the crater it produces. The result is applied to two different fragmentation models of the jet, and the resulting constraints imposed on quantities associated with the initial jet is derived. We indicate how analytical relationships of this sort may help to improve liner geometries by identifying those parts of the liner where the ‘‘optimum’’ requirement of fragmentation in the crater bottom is least satisfied. Crude arguments indicate that the use of variable angle—variable thickness liners can improve penetration depths by typically a few tens of percent relative to conventional, straight conical liners.

Effects of Jet Decay Rate Jet-Induced Loads on a Flat on Plate

Experimental modelling of the interaction between a jet and an aircraft wing or fuselage in VTOL aircraft was undertaken using a cold jet exiting perpendicular to a flat plate in a uniform cross-flow. Effects of jet decay rate and jet-to-cross-flow velocity ratio, R, on the induced load distribution were investigated. Jet decay rate was increased by using cylindrical centerbodies submerged in the jet nozzle, which caused nonuniform initial jet velocity profiles. Quicker jet decay rate, corresponding to the presence of a centerbody, resulted in as much as 50% reduction in the induced pressure loads on the plate. This has implications in interpretation of results from earlier VTOL model studies of jet induced loads, where the jets have often had relatively slow decay rates due to uniform initial velocity profiles

Analysis of separation control by means of tangential blowing

A computational procedure is described for predicting the critical jet momentum coefficient for achieving full potential lift by means of tangential blowing on airfoils with unslotted flaps. Among the applications of the procedure are the design and optimization of tangential blowing BLC systems for advanced fighter and transport type STOL aircraft and for over-the-wing blowing. The procedure incorporates a velocity profile with a velocity minimum, due to upstream boundary-layer and slot lip thickness effects, to describe the jet layer; and the initial jet velocity profile downstream of the slot exit contains an inviscid core region with a maximum velocity based on the total pressure inside the slot, rather than on empirical assumptions. The procedure utilizes the strip-integral technique to reduce the partial differential equations describing the jet layer flow to ordinary differential equations, and assumptions are made regarding the turbulent shear stress values at the boundaries and midpoints of each strip in order to carry out the integration. Computer programming of the procedure has been carried out, and a limited number of comparisons showing reasonably good agreement between the computational procedure and test results are shown.

A Theory of Edgetone Production

Edgetone frequencies f in stages 1, 2, 3, 4, etc., are given by fT=0.500, 1.230, 2.239, 3.242, etc., where T is the transit time of a particle across the aperture-edge gap. Jet slowing must be taken into account. For a turbulent jet, T = T0{[1 + (X/x0)]1 −1} with T0 = 2x0/3x0 and x0 = 5.75b; b is the slit width, x0 is the initial jet velocity, and X is the gap width. Conversely, X = x0{[1 + (T/T0)1−1}. For stage 1, the phase velocity at any point is twice the jet particle velocity there; for higher stages these velocities are essentially equal. The common opinion that the phase velocity is a fraction of the jet velocity resulted from misinterpretation of experimental data, neglect of jet slowing, and acceptance of idealized calculations as valid for edgetones. The present description agrees with all experimental data, including those observations wherein the frequency decreased as the 32 power of the gap width instead of the usually seen first power. A theory based on a perturbation calculation of the jet motion explains these results, and the operation of recorders, flutes, and organ pipes.

Review of stability of liquid jets and the influence of nozzle design

An attempt has been made to form a qualitative correlation between the nozzle shape and issuing jet shapé. The following points can be made: 1. (i) The major requirement of a nozzle is the efficient conversion of potential energy to kinetic energy. This is best achieved by a sudden, smooth contraction of the flow area from the supply line to the desired nozzle diameter. 2. (ii) The question of the angle of convergence appears uncertain. There would seem to be an optimum somewhere between 15° and 100°. It is possible that this optimum value might be a function of system dynamics and fluid properties. 3. (iii) The nozzle aspect ratio L/d has a highly significant effect on the initial jet velocity profile and subsequent jet surface shape up to L/d values where the shear stress and static pressure gradient are fully developed. In fact, the variability of L/d offers a means of control of the jet surface roughness over a considerable range. 4. (iv) There is some evidence favouring the rounding and polishing of the nozzle internal surfaces in order to achieve maximum performance. 5. (v) The theoretical hydrodynamic approach, involving numerical methods, should provide reasonable plug flow nozzles for systems where the liquid viscosity is low, viz. “water-like”.

Unsteady Boundary-Layer Flow of Power Law Fluids

It has been shown here that use of a skewed coordinate system, aligning the coordinate axes with the jet and the stream velocity vectors, can greatly simplify the description of the trajectories of turbulent jets discharging at various angles of inclination into a uniform cross stream and having various ratios between the initial jet velocity and the stream velocity. By aid of this skewed coordinate system and on the basis of dimensional and similarity considerations, the centerline trajectories of such jets appear to be very well correlated by a simple power law. The centerline trajectory and induced pressure field of the deflected jets also can be determined by integrating numerically the momentum equation from the given initial condition at the jet exit and with the entrainment coefficient and the crossflow drag coefficient chosen from the test data. Such calculations certainly are important for determining the pressure field induced by the deflected jet, but the present formula should provide a convenient and sufficient estimation of the centerline trajectory of the deflected jets.

Electric arc in a submerged gas jet

The results of photographic studies of the behavior of an electric arc in a submerged gas jet, using both regular photography and still and cine shadow photography, are presented. The interaction of the arc with the turbulent portion of the jet and the development of disturbances in the arc and the thermal layer around the arc dependent on initial jet velocity are noted. Experimentally obtained values for extent of the arc laminar zone, radius of arc thermal layer, and electric field intensity are compared with calculated values.

A Study on an Air-Jet Loom with Substreams Added

For scrutinizing the motion of weft gushed out and propelled by air stream, the physical (especially aerodynamic) properties of air jet and weft yarns are examined. An equation of motion for weft on an air jet loom is then derived, leading to the numerical solutions in several cases. The followings are some of the results: 1) The axial velocity of air jet is approximated fairly well by the following formula excepting the core region: V=BV0; /(x-A) where A and B are constants, V0; the initial jet velocity, x the axial distance from the nozzle exit to any point. 2) The coefficient of friction of spun yarns in air stream is approximated by Cf; =0.02+1/(V'+2) where V' is the relative air velocity to the yarn in m/sec. 3) In case where an air jet loom utilizes a measuring drum for yarn reserving, the drag due to yarn ballooning is as large as the air thrust. In order to minimize this harmful effect, a suitable cover should be set around the drum. 4) As the time necessary for the yarn to travel for some given distance is rather long in the region where the starting acceleration is not large, the initial jet velocity V0; should be quite large, say over 200m/sec.

A Study on Air-Jet Loom with Substream Added

The equation of weft motion on an air jet loom which pools the measured yarn by air stream is derived. This and the one reported in the previous paper which treats the measuring drum system are used to evaluate various weaving factors.The results are : (1) As the initial yarn-propelling-force is rather small when the air jet is used, the yarn in the nozzle may, without being gushed out, go back due to the air force when the pooling air is blown onto the whole of the recoverd yarn after gushing. Therefore the pooling air should be blown on the yarn one stage behind the recoverd yarn. (2) There are little difference in weaving speed even when the pooling system is so changed as pooling by air blown on the whole of the measured yarn, or pooling by air blown on one side of the measured yarn in loop form, or pooling in many loops. (3) Also little difference is shown between the measuring drum system and the air pool system in point of weaving speed. (4) However, the loom revolution can considerably be inhanced if the initial air jet velocity is increased, or if the yarn length blown by air at start is lengthened. (5) The weft length woven per unit time can be increased in case of the same yarn count as the reed space is broadened. The loom can be run faster in case of coarse yarn than in case of fine yarn as the reed space is broadened. (6) The following velocities are recommended : 60 m/sec for the uniform sub-stream along the shed, 20-30m/sec for air pooling.

A Study on Air-Jet Loom with Sub-Stream Added.

The equation of weft motion on an air jet loom which pools the measured yarn by air stream is derived. This and the one reported in the previous paper which treats the measuring drum system are used to evaluate various weaving factors.The results are : (1) As the initial yarn-propelling-force is rather small when the air jet is used, the yarn in the nozzle may, without being gushed out, go back due to the air force when the pooling air is blown onto the whole of the recoverd yarn after gushing. Therefore the pooling air should be blown on the yarn one stage behind the recoverd yarn. (2) There are little difference in weaving speed even when the pooling system is so changed as pooling by air blown on the whole of the measured yarn, or pooling by air blown on one side of the measured yarn in loop form, or pooling in many loops. (3) Also little difference is shown between the measuring drum system and the air pool system in point of weaving speed. (4) However, the loom revolution can considerably be inhanced if the initial air jet velocity is increased, or if the yarn length blown by air at start is lengthened. (5) The weft length woven per unit time can be increased in case of the same yarn count as the reed space is broadened. The loom can be run faster in case of coarse yarn than in case of fine yarn as the reed space is broadened. (6) The following velocities are recommended : 60 m/sec for the uniform sub-stream along the shed, 20-30m/sec for air pooling.