Experimental Investigations of the Effect of Reynolds Number on a Plane Jet (original) (raw)
Experimental analysis of low-Reynolds number free jets
Experiments in Fluids, 2009
The present paper analyzes the features of a low-Reynolds number free submerged jet with special regard to statistical quantities on the jet centerline. Measurements in an environment with very low disturbances allowed to observe details of turbulence and higher-order moments. Some peculiar features of the measured (natural) jet are shown to be in correspondence to observations referring to forced higher-Reynolds number jets. In particular, it is shown that, at low Reynolds numbers, the initial region of the jet is dominated by well-defined vortices in the shear layer. This result is substantiated by both the statistical moments and the spectral analysis. The presence of two distinct regimes is evidenced and discussed from a physical standpoint, also in relation to the mathematical analysis of the jet structure from the bibliography.
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...
A High Altitude-Low Reynolds Number Aerodynamic Flight Experiment
1999
A sailplane is currently being developed at NASA's Dryden Flight Research Center to support a high altitude flight experiment. The purpose of the experiment is to measure the performance characteristics of an airfoil at altitudes between 100,000 and 70,000 feet at Mach numbers between 0.65 and 0.5. The airfoil lift and drag are measured from pilot and static pressures. The location of the separation bubble and vortex shedding are measured from a hot film strip. The details of the flight experiment are presented. A comparison of several estimates of the airfoil performance is also presented. The airfoil, APEX-16, was designed by Drela (MIT) with his MSES code. A two dimensional Navier-Stokes analysis has been performed by Tatineni and Zhong (UCLA) and another at the Dryden Flight Research Center. The role these analysis served to define the experiment is discussed.
Experimental and quantitative investigation of a free round jet
The European Physical Journal Applied Physics, 2010
Flow visualization, basic image processing and statistical treatment are used to investigate the flow characteristics of an axisymmetric free air jet having an initially uniform velocity profile. Vortical structures and their development in the transition zone of the jet are visualized for a range of Reynolds numbers from 1300 to 1700. It is shown the onset and growth of these structures which propagate downstream of the nozzle exit at approximately 0.65 of the velocity of the mean flow. The duration of this development mechanism, before reaching the zone of turbulence, is estimated at 7.6 × 10 −3. Near-field and intermediate-field region lengths, separation distance between two neighboring vortical structures, apparition frequency and jet Strouhal number are measured as functions of the Reynolds number. In particular, it is shown that the Strouhal number, which is estimated at 0.64 in our case, is independent of Reynolds numbers.
Experimental and computational study of a high-Reynolds jet flow
Canadian Journal of Civil Engineering, 2017
Three-dimensional jet flows at high Reynolds (Re) numbers, namely over a million, have a significant importance in hydraulic engineering. Despite their importance, most of previous investigations have been mainly focused only on jet flows with orders of magnitude lower Re numbers. We present the results of an experimental campaign and a high fidelity largeeddy simulation (LES) to study a jet flow with Re ≈ 1.7 × 10 6 in a large-scale flume. Flow measurements are carried out using a pitot tube apparatus and the Virtual Flow Simulator (VFS-Geophysics) model is employed to simulate the flow field. The measured velocity field of the jet is used to evaluate the LES results. The presented experimental data for the cross-sectional velocity distributions at various distances from the jet source provide an unprecedented data-set for model validation at high Re numbers.
Fluid Dynamics of a High Aspect-Ratio Jet
9th AIAA/CEAS Aeroacoustics Conference and Exhibit, 2003
Circulation control wings are a type of pneumatic high-lift device that have been extensively researched as to their aerodynamic benefits. However, there has been little research into the possible airframe noise reduction benefits of a circulation control wing. The key element of noise is the jet noise associated with the jet sheet emitted from the blowing slot. High aspect-ratio jet acoustic results (aspect-ratios from 100 to 3,000) from a related study showed that the jet noise of this type of jet was proportional to the slot height to the 312 power and slot width to the 112 power. Fluid dynamic experiments were performed in the present study on the high aspect-ratio nozzle to gain understanding of the flow characteristics in an effort to relate the acoustic results to flow parameters. Single hot-wire experiments indicated that the jet exhaust from the high aspect-ratio nozzle was similar to a 2-d turbulent jet. Two-wire space-correlation measurements were performed to attempt to find a relationship between the slot height of the jet and the length-scale of the flow noise generating turbulence structure. The turbulent eddy convection velocity was also calculated, and was found to vary with the local centerline velocity, and also as a function of the frequency of the eddy. Nomenclature A-Area (typically of nozzle) AR-Aspect ratio a-Speed of sound a,,-Ambient speed of sound f-Frequency HARN-High aspect-ratio nozzle h-Slot height or rectangular nozzle height (small dimension) L-Characteristic length L L,-Length scale (streamwise direction) L,-Integral time scale M,-Convection Mach number-Characteristic length for the HARN, Leg = h 3/%1/4 M,-Jet centerline Mach number PIV-Particle image velocimetry p-pressure Re-Reynolds number R,-Space-correlation R,,-Cross-correlation w-width of rectangular nozzle (large dimension) V-Velocity V,-Turbulent eddy convection velocity Vj-Jet exit velocity (fully expanded) V,-Local jet centerline velocity x-Streamwise dimension, typically x = 0 is nozzle exit y-Dimension perpendicular to major axis of nozzle, y = 0 is center of nozzle z-Dimension along span of nozzle (parallel to major axis), z = 0 is center of nozzle Ax-Spacing between hot-wires in x-direction Ay-Spacing between hot-wires in y-direction p-density z-Time shift, used for cross-correlation
This paper gives an extensive presentation of the accessible experimental data bank of the ONERA Fundamental/Experimental Aerodynamics Department concerning high speed flows. Sophisticated non-intrusive measurements (3-component Laser Velocimetry, Particle Image Velocimetry, Coherent Anti-Stokes Raman Scattering, Pressure Sensitive Paint), flow visualisations (Electron Beam Fluorescence, Schlieren photography, Shadowgraphy) and more classical measurements have been used to the investigation of complex aerodynamic phenomena involved in jets, nozzle and base flows, air intakes and wing profiles. These experimental data contribute to the physical analysis of high speed flow interactions and they constitute “computable” test cases with perfectly defined limit conditions on typical geometries. The presented test cases are accessible under authorisation request with the ONERA-DAFE department. The motivation of this paper is to give rise to new numerical contributions and to favour Eastern...
Turbulent intensity and Reynolds number effects on an airfoil at low Reynolds numbers
Physics of Fluids, 2014
This work investigates the aerodynamics of a NACA 0012 airfoil at the chord-based Reynolds numbers (Re c) from 5.3 × 10 3 to 2.0 × 10 4. The lift and drag coefficients, C L and C D , of the airfoil, along with the flow structure, were measured as the turbulent intensity T u of oncoming flow varies from 0.6% to 6.0%. The analysis of the present data and those in the literature unveils a total of eight distinct flow structures around the suction side of the airfoil. Four Re c regimes, i.e., the ultra-low (<1.0 × 10 4), low (1.0 × 10 4-3.0 × 10 5), moderate (3.0 × 10 5-5.0 × 10 6), and high Re c (>5.0 × 10 6), are proposed based on their characteristics of the C L-Re c relationship and the flow structure. It has been observed that T u has a more pronounced effect at lower Re c than at higher Re c on the shear layer separation, reattachment, transition, and formation of the separation bubble. As a result, C L , C D , C L /C D and their dependence on the airfoil angle of attack all vary with T u. So does the critical Reynolds number Re c,cr that divides the ultra-low and low Re c regimes. It is further noted that the effect of increasing T u bears similarity in many aspects to that of increasing Re c , albeit with differences. The concept of the effective Reynolds number Re c,eff advocated for the moderate and high Re c regimes is re-evaluated for the low and ultra-low Re c regimes. The Re c,eff treats the non-zero T u effect as an addition of Re c and is determined based on the presently defined Re c,cr. It has been found that all the maximum lift data from both present measurements and previous reports collapse into a single curve in the low and ultra-low Re c regimes if scaled with Re c,eff .
The near field behavior of round jets at moderate reynolds numbers
The Canadian Journal of Chemical Engineering, 1984
The mean flow field of single round jets was studied at two values of Reynolds number, 13,000 and 22,000. Two nozzles, both of which were characterized by a square-edged entrance configuration and by values of length-to-diameter ratio (L / d) of 1 and 12, were used. The L / d = I nozzle produces ajet that decays and spreads more rapidly, and which entrains as much as three times more fluid than does the jet generated with the L/d = 12 nozzle. For axial locations up to 10 jet hole diameters, entrainment for each nozzle is essentially independent of Reynolds number, but Reynolds number effect is clearly in evidence at large axial locations, especially for the jet issuing from the longer nozzle. On a Ctudit le champ d'tcoulement moyen de jets d'un seul parcours pour deux valeurs de nombres de Reynolds, B savoir 13,000 et 22,000. On a utilist deux buses qui ttaient caracttristes par une configuration d'entr6e B bords carrts et par des valeurs du rapport (Lid) entre la longueur et le diambtre de 1 et 12. La buse dans laquelle L/d = 1 produit un jet qui dCcroit et s'btend plus rapidement et entraine jusqu'ti trois fois plus de fluide que ne le fait le jet produit avec la buse dans laquelle L/d = 12. Pour des positions axiales allant jusqu'h 10 fois le diamktre d'orifice du jet, I'entrahement pour chaque buse est essentiellement indtpendant du nombre de Reynolds, mais I'influence du nombre de Reynolds apparait clairement aux grandes valeurs des positions axiales, particulikrement dans le cas du jet produit avec la plus longue buse.