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This paper examines the effect of sound on the disturbance in the shear layer of a round jet with at a range of sound frequencies, from 200 Hz to 1 000 Hz at intervals of 100 Hz using pure tones and recordings of machines operating at different frequencies. Hot-wire velocity measurements, FFT analysis and flow visualization were used to reveal the shear layer structure. Since round jets are used in industrial applications, their environments are generally noisy, thus it is important to understand how the frequency of background sounds affect shear layer disturbance. When the frequency was varied the maximum disturbance was observed at 500 Hz, which coincides with the predominant frequency of a free jet. Spectral components in harmonics arose via nonlinear interaction as the disturbance moved downstream, and transition from laminar flow to turbulent flow progressed through vortex pairing and collapse. Pure tone and machine generated sound exhibited similar characteristics.

An experimental investigation has been carried out for the flow-induced sound in a grooved circular pipe. The length of the pipe is 500 mm, the inner diameter is 23 mm and the groove pitch is kept at 8 mm. The velocity in the pipe is varied from 6 m/s to 66 m/s. In the region of the velocity smaller than 30 m/s, the frequency of the sound generated in the pipe increases in the shape of stairs with increase of the velocity, and then resonant sound of the pipe generates from the pipe. When the velocity becomes large, the frequency of the sound increases linearly to the velocity. The shape of change of the frequency can be explained from characteristics of a cavity flow and lock-in phenomenon by the resonant frequency of the pipe.

When a fine screen is placed normal to vertically the axis of the jet, examined of the concerned with the self-sustained oscillation in a shear layer. Screens with several mesh sizes are employed. The screen is moved in the direction of the jet axis. The shear layer starts to oscillate periodically and simultaneously the characteristic of the self-sustained oscillation is examined from sound radiation in the screen vicinity. Flow visualization data suggest qualitatively the shear layer-screen interaction pattern and associated after passing through the screen.

The flow field around a circular cylinder elastically suspended with a cantilever-type plate spring in the jet impingement region was visualized to investigate the mechanism of the impingement heat transfer. The impingement distance H was kept constant at 3 or 5 times as large as the jet slot width, h = 15 mm.The Reynolds number was fixed at 10,000, or 5000 in the case of flow visualization. The self-induced periodic swing motion of the cylinder across the jet axis was caused by the interaction between the jet and the elastically suspended cylinder. It was found that this swing motion has direct effects on the flow and heat transfer characteristics of the stagnation region. The ensemble-averaged values of the flow velocity and its fluctuations depended on the cylinder diameter and the impingement distance. The local Nusselt number in the case of H/h = 3 with the oscillating cylinder of the smallest diameter D = 4 mm was increased to 1.15 times as large as that without the cylinder. The interesting patterns of the intermittency function defined with a certain threshold level of turbulence intensity were obtained under the above experimental conditions. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 313–330, 2001

One of the circular cylinders with several diameters was elastically suspended with springs in the jet impingement region between a jet slot and a heat transfer target plate. The slot-to-plate distance H was kept constant to be 3 or 5 times of the slot width, h=15mm. The Reynolds number was fixed at 10000, being exceptionally 5000 in the case of flow visualization. Periodical swinging motion of the cylinder across the jet was observed because of the cylinder vibration self-induced with the jet flwo. It was found that this vibration has direct effects on the characteristics of the flow and heat transfer around the stagnation region. The ensemble-averaged values of velocity and its fluctuation depend on the cylinder diameter and the impinging distance. The local Nusselt number in the case of H/h=3 with the vibrating cylinder of the smallest diameter D=4mm was increased up to 1.15 times of the Nusselt number without the cylinder. The interesting patterns of intermittency function defined together with threshold levels of turbulence intensity were observed in the above case.

The self-excited tone of a circular jet impinging upon a coaxial pipe can be give rise to not simply a single, however as many as well-defined frequency components in the rage of Reynoldsnumber (based on initial momentum thickness and jet velocity) 171gReg271. All of these components are traceble to the nonlinear interraction frequency of two primary components : the most stable frequency of the jet shear layer, β, and a low-frequency modulating component, β/2. The modulating component β/2 arises from vortex-vortex interaction at the impingiment edge. Its upsteram storongly modulates the sensitive regime of the shear layer at the nozzle lip. The most stable component can become sudden change (i.e. frequency down) when it is coincided with resonance of the air column in pipe.

The self-sustained oscillation is known to be excited by an axisymmetric jet impinging upon the sharp-leading edge of a ring. When a finite length of pipe, instead of a ring, is placed in a straight line with the jet axis, longitudinal resonant modes of the pipe are produced under a certain flow and geometerical conditions. In this paper, the influence of the inserted screen on the self-sustained oscillation and resonance of the pipe column oscillation are studied when a screen is placed between the nozzle exit and the ring or the pipe. Two patterns of the feedback loop are formed by the interaction between the vortical structure in the shear layer and the screen, or by the interaction between the former and the ring or the pipe. In the case of the pipe there are three frequency modes, namely oscillations in the two feedback loops and a resonant mode of the pipe. The resonance of the pipe is excited or suppressed according to the relationship among the three modes. When the screen is placed near the nozzle exit, the screen prevents the self-sustained oscillation and the resonance of the pipe dose not appear.

This paper is conerned with the self-excited oscillation in a shear layer of an axisymmetric jet when a fine screen is placed normal to the axis of the jet. The diameter of the nozzle exit is 28 mm and the exit velocity is 10.4 m/s corresponding to Reynolds number 1.99×104. Screens with three different mesh sizes are employed. In the experiment the screen is moved in the direction of the jet axis. The shear layer starts to oscillate periodically and simultaneously a pure tone is generated due to the impingement of the jet upon the screen. The frequency varies in the same way as in the jetring system. It is recognized that the configuration of the peaks in the velocity spectrum reflects that of the peaks in the sound spectrum. After passing through the screen, the periodic oscillation in the velocity remains at the location twice the nozzle diameter away from the screen.

Self-excited oscillation of an axisymmetric jet impinging upon a ring is investigated experimentally. The discreat vortices impinge upon the downstream sharp edge of the ring, in turn producing an upstream influence, thereby closing the loop for sustaining oscillations, as confirmed by the form of phase analysis of velocity and pressure signals. The fundamental frequency component exhibits an overall phase difference of (2nπ) +1/2 (n=0, 1, 2) between the nozzle lip and edge. Furthermore, the fundamental component propagates with phase speed, which is about 0.52∼0.59Uo. Spectral analysis of velocity fluctuation reveals multiple frequency components having substantial amplitudes relative to that of the fundamental frequency component ; using coherence analysis it is shown that the lowest frequency component can interact with the fundamental component either to reinforce itself or to produce an additional frequency component.

An experimental investigation has been carried out on the sound resonance associated with the circular pipe of finite length, which is positioned coaxially downstream of a round free jet. Self-sustained oscillations arises due to the impingement of the free shear layer on the pipe's leading edge, and this results in the periodic production of discrete ring vortices in the jet. The predominant frequency of oscillation is found to vary intrinsically with the position of the pipe's leading edge as in the case of the circular ring, in which several modal stages of oscillation have been observed previously. However, when this intrinsic predominant frequency approaches the first or higher eigen-frequencies of the pipe, sound resonance between these two frequency components occurs. Thus, the predominant frequency and the distance between the nozzle exit and the pipe's leading edge, when non-dimensionalized by the initial momentum thickness of the shear layer and the nozzle-exit velocity, should be the only parameters describing these sound resonance phenomena. In addition, the sound power level of the resonance increases nearly in proportion to the sixth power of the jet velocity.

Self-sustained oscillation of a shear layer has been experimentally investigated in an axisymmetric jet impinging on a sharp-edge ring. As many as five modal stages are identified with discrete changes of the dominant frequency as the distance between the jet-nozzle exit and the ring is changed. The dominant frequency observed in each stage can be correlated by a simple empirical equation when nondimensionalized with the initial momentum thickness of the shear layer. The frequency change between two successive stages is also shown to obey a general rule of modal transition. An analysis of the phase-lag of velocity signals at various streamwise locations reveals a downstream travelling wave, while the associated vortex formation is confirmed by smoke-wire flow-visualization.

(1) The seasonal changes in the contents of dissolved inorganic salts, organic substances and the number of bacteria were measured in three pools of Tokyo in 1952 and 1953. The interrelation between these three were also investigated.(2) The amounts of NH4-N of the surface layer was 0.010.042 mg/l in pool A, 0.030.83 mg/l in pool B, and 0.010.64 mg/l in pool C. In all the pools the maximum concentrations were seen in spring and autumn, and the minimum onesin winter and summer. The amount was always larger at the bottom layer than at the surface layer.The difference of the amounts of NO2-N and NO3-N between the surface and the bottom layers was very small, the former being 00.007 mg/l and the latter 00.08 mg/l, both of which decreased to zero in spring and autumn. The concentration in pool A was lower than in any other pools in general.(3) The content of organic-N showed two maxima every year. It was high in spring and in autumn, and low in winter and in summer in all the pools. At the surface layer it was about 0.530.76 mg/l, being lower than in the bottom layer. The content in pool A was lower than those in any other pools.(4) Among the phosphorus compounds, the amount of PO4-P was 00.008 mg/l in pool A and B, 00.003 mg/l in pool C. It became zero in the surface layer in spring and summer, and in every layer in autumn. The content of total P was 0.010.19 mg/l, which was 24 times as much in pool C as in the other pools.(5) The concentrations of the above minerals in each pool was nearly agreeable with those which were seen in neutral dystrophic lakes.(6) The reciprocal relations were seen among the amount of dissolved salts and the amount of albuminoid-N, organic-N or chlophyll content. The relationship was especially marked in the case of chlorophyll content.(7) The measurement of bacterial number was made monthly by the method of plate culture. The bacterial numbers were between ×102-103 per cc water of the pools and were fewer than those of eutrophic lakes. Two maxima and two minima occurred during 1952. The maxima were seen in spring and autumn, and the minima in winter and summer. In 1953 no tremendous abundance occurred, and a minimum was seen during the summer stagnation.(8) It was recognized that bacteria increased in general during the time of optimum temperature (1025°C). However, even in that time they decreased in accordance with the increase of Protozoa and Protophyta or with the shortage of dissolved oxygen.(9) The maximum size of bacterial population appeared at the same time with the maximum of chlorophyll content ; or, the latter followed immediately the former. The increase in the dissolved salts was seen at the same time with or immediately after the increase in bacterial population. The increase of chlorophyll followed the increase of salts.(10) The amount of inorganic salts was 40400 times as much in the living body as in the pool water.(11) According to physiological analyses, the minimum element in the water of pools for biological production seemed to be P rather than N. This shortage of phosphorus was considered to be caused by the abundance of humic substances.

Carbon cycle in Lake Suwa (maximum depth : 6.7 m;area : 14.5 km2) which is a highly polluted and eutrophic lake in Nagano Prefecture, Japan, was studied by determining pH and total carbon dioxide as follows :(1) Total carbon dioxide (Total CO2) of the lake water was determined by KOYAMA's method. The same water sample was aerated in order to be equilibrated with air. Total CO2 of the aerated water sample was determined as an original total carbon dioxide (Orig. CO2).In the stably stratified lake waters, the difference (ΔCO2) between Orig. CO2 and Total CO2 corresponds to the net fixation of CO2 (N. Fix. CO2) in a case of positive value and the net formation of CO2 (N. Form. CO2) in a case of negative value.In the case of Lake Suwa, however, it should be suitable to call the former as the preserved amount of net fixation of CO2 (P. A. N. Fix. CO2) and the latter as the preserved amount of net formation of CO2 (P. A. N. Form. CO2), because the lake water layers are easily mixed and some of the dissolved CO2 may be exchanged for the atmospheric CO2 through all seasons.From a vertical distribution of ΔCO2, P. A. N. Fix. CO2 or P. A. N. Form. CO2 in a water column was calculated on the basis of (g C/m2).(2) Relation curves between pH and Total CO2 of the lake water were constructed from pH and Total CO2 values obtained from the water samples collected in different months.(3) Greater part of the numerous data of Total CO2 values used in this study were estimated from a large number of vertical distributions of pH values obtained at different times in different days while comparing with the relation curves between pH and Total CO2.(4) Average P. A. N. Fix. CO2 (A. P. A. N. Fix. CO2) and average P. A. N. Form. CO2 (A. P. A. N. Form. CO2) in a whole day were estimated from the values of P. A. N. Fix. CO2 and P. A. N. Form. CO2 in a water column, which were estimated at different times in the day.(5) Numerous data of these A. P. A. N. Fix. CO2 or A. P. A. N. Form. CO2 in the water column were estimated on different days in different months.(6) A histogram of A. P. A. N. Fix. CO2 and A. P. A. N. Form. CO2 was then constructed against months.(7) This histogram shows the following facts : (a) A. P. A. N. Fix. CO2 ranged between 3.8 and 6.6 g C/m2 from April through August. (b) A. P. A. N. Form. CO2 ranged between -8.2 and -12.9 g C/m2 from September through December. (c) On the assumption that the average exchangeability of CO2 between air and lake water in a month is similar to those of the adjacent months, the difference between A. P. A. N. Fix. CO2 or A. P. A. N. Form. CO2 of a month and that of an adjacent month corresponds to the average net fixation rate of CO2 during the two months in a case of positive value and to the average net formation rate of CO2 in a case of negative value. (d) The average net fixation rate of CO2 and the average net formation rate of CO2 correspond to the average net production rate and the average net decomposition rate of organic matter respectively.(8) The maximum net production rate which was found between March and April amounted up to 4.5 g C/m2. day and the maximum net decomposition rate which was found between August and September amounted up to-13.5 g C/m2. day.