Experimental Investigations of the Effect of Reynolds Number on a Plane Jet (original) (raw)
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On the role of initial conditions on a turbulent plane jet: The role oif nozzle exit area
The dependence of statistical flow properties of a turbulent plane jet on the nozzle-exit area was investigated experimentally. Jet flows from three plane nozzles were measured using hot wire anemometry at an identical Reynolds number (Re = U co H / ) of 9,000 and nozzle aspect ratio of 36, but with nozzle-exit areas of A = 900 mm 2 , 3600 mm 2 and 14400 mm 2 , whereby U o,c was the mean exit velocity, was the kinematic viscosity of air, and H was the slot opening width. Results demonstrated a longer potential core and a higher decay rate for the case with a larger nozzle-exit area. The centerline turbulence intensity (u*) showed a strong dependence on A in the near field but this dependence weakened progressively as the jet propagated downstream. The jet flow from the nozzle with a larger exit area produced a relatively higher near field turbulence intensity, indicating a significant dependence of near field vortical structures on the nozzle-exit area. The centerline turbulence intensity profiles became selfsimilar, collapsing on a single curve only for x/H 10. Overall, the dependence of the mean and turbulent velocity field on nozzle-exit area was significant, confirming the influence of initial and boundary conditions.
The influence of nozzle-exit geometric profile on statistical properties of a turbulent plane jet
Experimental Thermal and Fluid Science, 2007
The paper reports an investigation of the influence of geometric profile of a long slot nozzle on the statistical properties of a plane jet discharging into a large space. The nozzle-exit profile was varied by changing orifice-plates with different exit radii (r) over the range of 0 < r/h < 3.60, where h is the slot-height. The present measurements were made at a slot-height based Reynolds number (Reh) of 1.80 × 104 and a slot aspect ratio (span/height) of 72. The results obtained show that both the initial flow and the downstream flow are dependent upon the ratio r/h. A “top-hat” mean exit velocity profile is closely approximated when r/h approaches 3.60. The decay and spread rates of the jet’s mean velocity decrease asymptotically as r/h is increased, with the differences becoming small as r/h approaches 3.60. A decrease in r/h results in a higher formation rate of the primary vortices in the near-field. The far-field values of the centerline turbulence intensity are higher for smaller r/h, and display asymptotic-like convergence as r/h approaches 3.60. Overall, the effect of r/h on the mean and turbulence fields decreases as r/h increases.
Five round jets at Mach number 0.9 and diameter-based Reynolds number 10 5 originating from a pipe nozzle are computed by Large-Eddy Simulations using grids of 252 million points. In the pipe, the boundary layers are tripped, in order to obtain, at the exit section, laminar mean velocity profiles of momentum thickness equal to 1.8% of the jet radius, and peak turbulence intensities of 0, 3, 6, 9 and 12% of the jet velocity. The influence of initial turbulence on flow development is thus investigated. As the nozzle-exit turbulence level increases, the coherent structures typically found in initially laminar jets gradually disappear, which leads to shear layers spreading at lower rate with strongly reduced rms fluctuating velocities. The jets also develop farther downstream, resulting in longer potential cores.
Investigating One-Dimensional Turbulence Intensity of Circular and Non-Circular Jets
International Journal of Research and Scientific Innovation (IJRSI), 2019
─ Fluid dynamics and heat transfer sectors have undergonerevolutionary improvements with the study of turbulent flow in recent decades and still different ongoing researches are making breakthroughs in those sectors. In this research, the fluctuation of pressure in the flow field was measured using differential pressure transducer to investigate the turbulence region of conventional circular jet as well as non-circular (rectangular, square and triangular) jets in the flow axis only. The method was approached to introduce a cost-efficient technique as the alternative of high-cost particle image velocimetry, acoustic Dopplervelocimetry. The objective was to investigate the change in turbulence characteristics of different jets and compare performance which can be applied to aerodynamics, propulsion, heat transfer or environmental studies. Simultaneous measurements of pressure in the flow field were taken using pitot-tube which was converted into velocity applying dynamic pressure theory. The jet flow was created using a blower in an airflow facility and the area of inlet and outlet of all the nozzle was equal to maintain the initial jet flow characteristics. The turbulent intensity, mean shear layer and potential core length of the jets have been derived from the measured data. The study revealed that square nozzle didn't have a significant impact in the flow field whereas the rectangular jet had an increased average shear layer and the triangular jet had a decreased potential core length compared to the conventional jet.
Examination of Reynolds number effect on the development of round jet flow
EUREKA: Physics and Engineering, 2021
In this study, the Reynolds number effect on the development of round jet flow is presented. The jet is produced from a smoothly contracting round nozzle and the flow structure is controlled by varying the air blower speed in order to obtain various Reynolds numbers (Re). The flow Reynolds number considered varies between 1140 and 9117. Mean velocity measurements were taken using hot-wire probe at different axial and lateral distances (0≤x/d≤50, where x is the downstream distance and d is the nozzle diameter) for the jet flow and at for 0≤x/d≤30 in long pipe attached to the nozzle. Measurements reveal that Reynolds number dictate the potential core length such that the higher the Reynolds number, the lower the potential core which is a measure of mixing of jet and ambient fluid. It shows that further away from the jet exit section, potential core decreases as Reynolds number increases, the velocity profile has a top hat shape very close to the nozzle exit and the shape is independen...
Flow structure and turbulence in near fields of circular and noncircular jets
Progress in Flight Physics, 2012
Experimental investigation of the turbulent §ow ¦eld of jets emanating from circular and curved-edged noncircular nozzles is conducted using hotwire anemometry. Distributions of the mean velocity vector are obtained by traversing a triple-sensor hot-wire probe at varying streamwise locations downstream of the jet exit plane in a low-speed free-jet facility. Measurements are obtained for a baseline circular nozzle (round jet) and for equilateral triangular and square nozzles. The data are used to compare the structure of the §ow ¦eld within these jets such as their mean velocity, turbulent kinetic energy, and entrainment levels. Axis rotation phenomenon is also investigated for noncircular nozzles, and it was not observed up to a streamwise location of 10d (d is the nozzle equivalent diameter, equals to 40 mm) for noncircular nozzles.
Influence of Nozzle Configuration on the flow field of Multiple Jets
2017
Turbulent jet flows with multiple nozzle inlets are investigated computationally using OpenFOAM. The configurations vary from single to five axisymmetric nozzles. First order closure is used with Reynolds Averaged Navier-Stokes equations. Computed results are compared with the available experimental data. The effect of nozzle configuration on the jet flow field is discussed with predicted mean flow and turbulent flow data. Near field of multiple jets shows non-linear behavior. Multiple jets show better performance in the near field based on entrainment, secondary flows and area averaged turbulent kinetic energy. The downstream evolution of multiple jets differs for configurations with and without central jet. The shape parameter confirms the evolution of multiple jets towards an axisymmetric jet.
Comparison of turbulent jets issuing from rectangular nozzles with and without sidewalls
Experimental Thermal and Fluid Science, 2007
This paper reports a systematic study of a turbulent jet issuing from a rectangular slot nozzle of high-aspect ratio, AR (≡ w/h, where w and h are the long and short sides of the slot, respectively) tested with and without sidewalls. The solid sidewalls were flush with each of the slot’s short sides vertically and extend axially along the streamwise direction of the jet. Hot-wire measurements were conducted at a Reynolds number based on slot-width (h) and exit centerline velocity of Reh ≈ 7000 (for AR = 30 and 60) and at 10,000 (for AR = 30) up to 160 h downstream. All jets have a potential core in which the local centerline velocity is approximately constant, followed by a transition region and then a statistically two-dimensional (2-D) region where the centerline mean velocity, Uc ∼ x−1/2. The potential core of the jet without sidewalls is shorter than that with sidewalls. Near field power spectral analysis reveals that the primary vortex shedding rate is higher for the jet without sidewalls than the jet with sidewalls. The 2-D region of the jet with sidewalls is found to extend over a longer axial distance than that of the jet without sidewalls. It is also demonstrated that both the decay and spread rates of the jet within the 2-D region are lower for the case with sidewalls. Beyond the 2-D region, the jet without sidewalls enters into a far field transitional phase and then tends to behave statistically like an axisymmetric jet with Uc ∼ x−1. The centerline turbulence intensity of the jet with sidewalls becomes asymptotic closer to the nozzle exit than the jet without sidewalls. The skewness and flatness factors confirm further statistical differences between the jet with and without sidewalls.
Study of the Flow Characteristics of Swirling Confined Jet
Research and Scientific Innovation Society Conferences, 2020
Axial mean velocity is the primary criteria of most of the flow field. In the present investigation, the mixing of swirling jet within the solid boundary and the wake position memory as it came out of the solid boundary was studied. Extension tubes of 105mm, 210mm and 315m length were fitted to 30 degree and 60 degree swirling nozzle which were made by fitting triangular shaped double start wedge shaped helical right hand thread inside the pipe nozzle. Height of these wedges were 27.5mm, leaving a clear opening of 25mm diameter in the central zone of the 80mm diameter pipe nozzle. Data of axial mean velocity at the exit of the extension tubes were recorded at Reynolds number 5.3e4.
Flow, Turbulence and Combustion, 2009
In this paper we present the experimental results of a detailed investigation of the flow and acoustic properties of a turbulent jet with Mach number 0•75 and Reynolds number 3•5 10 3. We describe the methods and experimental procedures followed during the measurements, and subsequently present the flow field and acoustic field. The experiment presented here is designed to provide accurate and reliable data for validation of Direct Numerical Simulations of the same flow. Mean Mach number surveys provide detailed information on the centreline mean Mach number distribution, radial development of the mean Mach number and the evolution of the jet mixing layer thickness both downstream and in the early stages of jet development. Exit conditions are documented by measuring the mean Mach number profile immediately above the nozzle exit. The fluctuating flow field is characterised by means of a hot-wire, which produced radial profiles of axial turbulence at several stations along the jet axis and the development of flow fluctuations through the jet mixing layer. The axial growth rate of the jet instabilities are determined as function of Strouhal number, and the axial development of several spectral components is documented. The directivity of the overall sound pressure level and several spectral components were investigated. The spectral content of the acoustic far field is shown to be compatible with findings of hot-wire experiments in the mixing layer of the jet. In addition, the measured acoustic spectra agree with Tam's large-scale similarity and fine-scale similarity spectra (Tam et al., AIAA Pap 96, 1996).