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A five-velocity-component LDV system was designed to make five nearly simultaneous velocity component measurements: coincident instantaneous U, V, W components of the velocity at one point and two V velocity components at two near...
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A five-velocity-component LDV system was designed to make five nearly simultaneous velocity component measurements: coincident instantaneous U, V, W components of the velocity at one point and two V velocity components at two nearby locations. The research is aimed at examining the relations among measured velocity components in order to investigate the near wall turbulence structure of 3D turbulent boundary layers (3DTBLs) and aid in the development of new turbulence models for 3D subsonic pressure-driven turbulent boundary layer (TBL). To map the relations between the 'sweeps' and 'ejections' of near wall turbulent fluid, two V measurement points can be traversed within a selected domain. In order to map the velocity field for given V measurement locations, a U, V, W measurement point is traversed in a domain defined by the two V measurement points. At the same time, the system can make measurements throughout the whole boundary layer to investigate other phenomena. Data from this system show that the uncertainties are low and the repeatability of measurements is excellent. Data presented include the mean and fluctuation velocities, shear stresses, some of the triple velocity fluctuation correlations and some auto and cross correlation coefficients obtained at one measurement station of a high Reynolds number 3DTBL flow. [References: 12]
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This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and ...
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This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and turbulence intensity (T.I.) influence the wing-junction flow was also studied. The junction-flow structures at low Reynolds numbers were visualized using the smoke-wire technique. The smoke-streak flow patterns were classified into two characteristic modes - horseshoe vortex and non-horseshoe vortex. The horseshoe-vortex patterns were further categorized as the junction-vortex mode and non-junction-vortex mode. The velocity vectors were measured using the particle-image velocimetry (PIV), and the data was utilized to calculate the junction vorticity (Ω). Experimental results indicate that the straight wing has the maximum junction vorticity. The Ω decreases with increasing α and Λ and with decreasing Re. The Ω decreases with increasing T.I. The upstream T.I. generated by the mesh fences was more significant than that produced by sandpapers.
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This study utilized the NACA 0012 finite wings to investigate the effects of wing sweep angle Λ and angle of attack (α) on the junction vortex at Re = 8 × 10~4. The junction-vortex structures are visualized using the surface oi...
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This study utilized the NACA 0012 finite wings to investigate the effects of wing sweep angle Λ and angle of attack (α) on the junction vortex at Re = 8 × 10~4. The junction-vortex structures are visualized using the surface oil-flow visualization. The junction vortex is classified as - separation, attached, bubble, and bluff-body wake modes. The separation mode occurs at Λ ＜ 12° and α＜ 5°. The attached mode occurs at low α for a swept-back wing (Λ ＞ 0°) and the bluff-body wake mode occurs at high α for a forward-swept wing (Λ ＜ 0°). Furthermore, the bubble mode occurs at high sweep angle (i.e., high backward sweep angle) and high angle of attack. Moreover, the properties of velocity vectors, normal stress and shear stress are also detected and analyzed using an X-type hot-wire anemometer.
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A three-dimensional, pressure-driven turbulent boundary layer created by an idealized wing-body junction flow was studied experimentally. The data presented include time-mean static pressure and directly measured skin-friction mag...
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A three-dimensional, pressure-driven turbulent boundary layer created by an idealized wing-body junction flow was studied experimentally. The data presented include time-mean static pressure and directly measured skin-friction magnitude on the wall. The mean velocity and all Reynolds stresses from a three-velocity-component fibre-optic laser-Doppler anemometer are presented at several stations along a line determined by the mean velocity vector component parallel to the wall in the layer where the (
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Four high-frequency-response pressure transducers with 10 viscous units resolution each have been used to obtain simultaneously the fluctuating pressure gradients at the wall of a zero-pressure-gradient boundary layer and then to ...
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Four high-frequency-response pressure transducers with 10 viscous units resolution each have been used to obtain simultaneously the fluctuating pressure gradients at the wall of a zero-pressure-gradient boundary layer and then to compute the vorticity flux away from the wall. Since the viscous force on an element of incompressible fluid is determined by the local vorticity gradients, understanding of their dynamical characteristics is essential in identifying the turbulent structure. Extremely high and low amplitudes of both vorticity gradients have been observed which contribute significantly to their statistics although they have low probability of appearance. The r.m.s. of the vorticity flux when scaled with inner wall variables depends very strongly on the Reynolds number, indicating a breakdown of this type of scaling. The application of a small threshold to the data indicated two preferential directions of the vorticity flux vector. An attempt has been made to identify these high- and low-amplitude signals with physical phenomena associated with bursting-sweep processes. Vortical structures carrying bipolar vorticity are the dominant wall structures which are associated with the violent events characterized by large fluctuations of vorticity flux. [References: 59]
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A junction flow formed between a wing and a wall is ubiquitous in engineering applications and impacts aerodynamic performance and energy consumption. This paper studies the mean pressure field in the junction region around wall-m...
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A junction flow formed between a wing and a wall is ubiquitous in engineering applications and impacts aerodynamic performance and energy consumption. This paper studies the mean pressure field in the junction region around wall-mounted wings with NACA 0012 and NACA 6412 wing section profiles. Mean surface pressure measurements have been performed in the University of New South Wales large aerodynamic wind tunnel at a chord-based Reynolds number of 87,000 and a range of angles of attack spanning 0-12 degrees. Results of three-dimensional RANS simulations for both wing profiles using five turbulence models are also presented. The experimental results show that the wall significantly changes the mean pressure distribution around the wing, especially in the region upstream of the boundary layer reattachment point. The gamma-Re theta SST turbulence model has a transition predictor for the boundary layer above the airfoil far away from the bottom wall and delivers the most accurate pressure field prediction in the wing-wall junction region. The junction pressure structure is well-captured except the LE stagnation region and the suction side of the trailing edge. The Reynolds Stress models, however, do not show any advantage in predicting the mean pressure field at high angles of attack.
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The three-dimensional flow separation over the Rood wing-body junction is an exemplar application of separation affecting many important flows in turbomachinery and aerodynamics. Conventional Reynolds Averaged Navier Stokes (RANS)...
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The three-dimensional flow separation over the Rood wing-body junction is an exemplar application of separation affecting many important flows in turbomachinery and aerodynamics. Conventional Reynolds Averaged Navier Stokes (RANS) methods struggle to reproduce the complexity of this flow. In this paper, an unconventional use is made of a hybrid Reynolds Averaged Navier Stokes (RANS) model to tackle this challenge. The hybridization technique combines the Menter k-ω-SST model with the one equation sub-grid-scale (SGS) model by Yoshizawa through a blending function, based on the wall-normal distance. The hybrid RANS turbulence closure captured most of the flow features reported in past experiments with reasonable accuracy. The model captured also small secondary vortices at the corner ahead of the wing nose and at the wing trailing edge. This feature is scarcely documented in the literature. The study highlights the importance of the spatial resolution near the wing leading edge, where this localized secondary recirculation was observed by the hybrid RANS model. It also provides evidence on the applicability of the hybrid Menter and Yoshizawa turbulence closure to the wing-body junction flows in aircraft and turbomachines, where these flows are characterized by a substantially time-invariant three-dimensional separation.
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Experimental flow measurements are presented for a wing-body junction flow obtained using laser-Doppler velocimetry. Mean velocity and Reynolds stress data are used to calculate the complete transport-rate budgets of Reynolds stre...
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Experimental flow measurements are presented for a wing-body junction flow obtained using laser-Doppler velocimetry. Mean velocity and Reynolds stress data are used to calculate the complete transport-rate budgets of Reynolds stresses and turbulent kinetic energy. The measurements were carried out in the Virginia Tech Boundary Layer Tunnel at a nominal air speed of 27.5 m/s around a NACA 0020 tail and 3:2 elliptical nose wing shape. Data are presented for a two-dimensional turbulent boundary layer (2DTBL), a strongly skewed three-dimensional turbulent boundary layer (3DTBL), a location in the vicinity of a 3-D separation line, and around the center of the vortex in the horse-shoe vortex that forms around the wing. Terms in the transport-rate equations were calculated also using the measured triple order fluctuating velocity products. Results show that the pressure-diffusion approximated by Lumley [Lumley, J.L., 1978. Computation modeling of turbulent flows. Adv. Appl. Mech. 18, 124-176] is an important term in the balance of v~2, uv, and vw stress budgets; there were distinct differences between the two-dimensional and three-dimensional turbulent boundary layer budgets. Qualitative comparisons of experimental stress-transport-rate budgets to previous DNS results show a better agreement using the aniso-tropic dissipation rate of Hallbaeck et al. [Hallbaeck, M., Groth, J., Johansson, A.V., 1990. An algebraic model for nonisotropic turbulent dissipation rate in Reynolds stress closure, October. Phys. Fluids A 2 (10), 1859-1866].
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Laser-Doppler velocimeter measurements of a wing/body junction flow field made within a plane to the side of the wing/wall junction and perpendicular both to a 3:2 elliptical nose—NACA 0020 tail wing, and a flat wall are presente...
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Laser-Doppler velocimeter measurements of a wing/body junction flow field made within a plane to the side of the wing/wall junction and perpendicular both to a 3:2 elliptical nose—NACA 0020 tail wing, and a flat wall are presented. Reynolds number of the approach boundary layer was, Re_θ = 5940, and free-stream air velocity was, U_(ref) = 27.5 m/s. A large vortical structure residing in the outer region redirects the low-turbulence free-stream flow to the vicinity of the wing/wall junction, resulting in thin boundary layers with velocity magnitudes higher than free-stream flow. Lateral pressure gradients result in a three-dimensional separation on the uplifting side of the vortex. Additionally, a high vorticity vortical structure with opposite sense to the outer-layer vortex forms beneath the outer-layer vortex. Normal and shear stresses increase to attain values an order of magnitude larger compared to values measured in a three-dimensional boundary layer just outside the junction vortex. Bimodal histograms of the w fluctuating velocity occur under the outer-layer vortex near the wall due to the time-dependent nature of the horseshoe vortex. In such a flow the shear-stress angle (SSA) highly lags the flow-gradient angle (FGA), and the turbulence diffusion is highly altered due to presence of vortical structures.
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Turbulent junction flow is commonly seen in various turbomachinery components, heat exchangers, submarine appendages, and wing-fuselage attachments, where the approach boundary layer separates and rolls up into a coherent system o...
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Turbulent junction flow is commonly seen in various turbomachinery components, heat exchangers, submarine appendages, and wing-fuselage attachments, where the approach boundary layer separates and rolls up into a coherent system of vortices upstream of a wall-mounted bluff body. One of the signature features of this flow is its tendency to switch randomly between two semi-stable states. The highly unsteady behavior causes high pressure fluctuations on the wall and obstacle surfaces and high heat transfer. Despite its prevalence, few studies have examined the Reynolds number dependence of the dynamic junction flow behavior. In this paper, the flow physics as well as heat transfer of the turbulent junction flow are investigated using high speed particle image velocimetry and time-average infrared thermography measurements. A wide range of approach momentum thickness Reynolds numbers are studied, ranging from 550 to 5740. Although the time-mean flowfield does not show significant Reynolds number dependency, the normalized turbulent kinetic energy in and around the vortex core increases with Reynolds number, and the high heat transfer associated with the junction flow moves closer to the junction. These effects are linked to the increasing randomness in the position of the primary junction flow vortex as the Reynolds number increases. (C) 2019 Elsevier Ltd. All rights reserved.
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