Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session NR: Turbulent Boundary Layers: Jets, Wakes and Gradients |
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Chair: William Saric, Texas A & M University Room: Hilton Chicago Stevens 3 |
Tuesday, November 22, 2005 11:01AM - 11:14AM |
NR.00001: Nonisotropic turbulence: A turbulent boundary layer Kunlun Liu, Richard Pletcher The probability density function (PDF) and the two-point correlations of a flat-plate turbulent boundary layer subjected to the zero pressure gradient have been calculated by the direct numerical simulation. It is known that the strong shear force near the wall will deform the vortices and develop some stretched coherent structures like streaks and hairpins, which eventually cause the nonisotropy of wall shear flows. The PDF and the two-point correlations of isotropic flows have been studied for a long time. However, our knowledge about the influence of shear force on the PDF and two-point correlations is still very limited. This study is intended to investigate such influence by using a numerical simulation. Results are presented for a case having a Mach number of $M=0.1$ and a Reynolds number 2000, based on displacement thickness. The results indicate that the PDF of the streamwise velocity is Lognormal, the PDF of normal velocity is approximately Cauchy, and the PDF of the spanwise velocity is nearly Gaussian. The mean and variance of those PDFs vary according to the distance from the wall. And the two-point correlations are homogenous in the spanwise direction, have a slightly variation in the streamwise direction, but change a lot in the normal direction. $R_{ww}$ or $R_{vv}$ can be represented as elliptic balls. And the well-chosen normalized system can enable $R_{ww}$ and $R_{vv}$ to be self-similar. [Preview Abstract] |
Tuesday, November 22, 2005 11:14AM - 11:27AM |
NR.00002: A Spatio-Temporal Decomposition of the Coherent Structures in the Three-Dimensional Wall Jet Joseph Hall, Daniel Ewing The most noteworthy feature of the turbulent three-dimensional wall jet is that the growth of the jet parallel to the wall is roughly 5 times larger than the growth of the jet normal to the wall. This makes this flow particularly attractive for film cooling applications. The dynamics of the organized turbulent motions in the three-dimensional wall jet were examined using simultaneous measurements of the velocity and fluctuating wall pressure field. A Proper Orthogonal Decomposition (POD) of the fluctuating pressure field in the lateral direction indicated that the majority of energy was relatively evenly split between a symmetric and antisymmetric mode. The interplay of these two modes caused poor correlation of the fluctuating pressure across the centerline of the jet. A combined spatial and temporal decomposition of the reconstructed pressure field using the contribution of the first two POD modes revealed the presence of two types of large-scale structures in the flow: one with a higher characteristic frequency located near the the centreline of the jet, and a second with a much lower characteristic frequency that was coincident across at least one half of the jet. Pressure-velocity correlations of the temporally bandpass filtered contribution of the dominant POD modes indicated that these two events were significantly different. [Preview Abstract] |
Tuesday, November 22, 2005 11:27AM - 11:40AM |
NR.00003: Interaction of Multiple Adjacent Jets in Cross Flow Ephraim Gutmark, Irene Ibrahim Subsonic wind tunnel experiments are conducted to study the behavior of multiple adjacent jets exhausting into cross flow. The interaction between the jets and the effect of one jet on the other(s) relative to single jet in cross-flow, is investigated. Parameters studied include: distance between the jets, their alignment, injection momentum and angle, and jets shape and diameter. The comparison is based on the analysis of penetration, spread and rate of decay of each jet as compared to the other(s) and to single jets. The size, location, distribution and magnitude of characteristic regions within the flow such as the reverse flow and wake regions is studied. Quantitative velocity fields are obtained using Stereoscopic Particle Image Velocimetry (SPIV). In a single jet in cross-flow, mixing and freestream entrainment are interdependent and the mixing mechanisms which take place in the wake region are different from those in the jet region. In the wake region vertical vortices actively entrain fluid from the freestream and enhance mixing. This study extends this knowledge into the realm of multiple jets. [Preview Abstract] |
Tuesday, November 22, 2005 11:40AM - 11:53AM |
NR.00004: Experimental Measurements of a Cylindrical Turbulent Boundary Layer in a Submarine Wake Deborah Furey, Thomas Forlini, Damien Bretall, Kimberly Cipolla High resolution stereo-PIV measurements were made on a long, small diameter cylinder towed from the control surface of a 1/18$^{th}$ scale submarine model. The experiments were performed in the Deep Water Tow Basin at NSWCCD at 5 kts. An instrumented mounting stock for the horizontal control surface measured the differential load due to cylinder drag force. Three-dimensional velocity fields over ten body lengths downstream were obtained. The cylinders were approximately neutrally buoyant and towed through a stationary laser sheet oriented perpendicular to the tow direction. The objective of the study was to quantify the effect of the flow behind the submarine control surfaces and propeller on the boundary layer development and dynamics of a model towed array where $\delta >>$ the cylinder radius, a. Results with and without a propeller will be presented. Approximately 40 instantaneous vector fields were obtained for each location. Mean and fluctuating streamwise and cross-stream velocities and vorticity were computed. Initial results indicate that the wake has significant effects on the dynamics and hydrodynamics of the cylinder. [Preview Abstract] |
Tuesday, November 22, 2005 11:53AM - 12:06PM |
NR.00005: Experimental Measurements of the Turbulent Boundary Layer on a Towed Array Model Kimberly Cipolla, David Hart, William Keith, Deborah Furey, Paisan Atsavapranee Experimental measurements were made of the boundary layer growth and associated mean wall shear stress along varying lengths of a towed array model. Inert towed array modules (approximately 3.68 cm in diameter, and up to 125 m long) were towed in the NSWCCD High Speed Tow Basin at tow speed values of 7.5, 15, 25 and 30 kts. The objective was to provide data on long thin cylinders at zero angle of attack to determine the hydrodynamic loading and axisymmetric turbulent boundary layer development on towed arrays. Three-dimensional velocity field measurements were obtained over the length of the cylinders with a stationary Stereo-PIV system. Simultaneous measurements of total drag were obtained for each cylinder with an underwater load cell rigidly attached to the tow point at the base of the strut and used to compute the tangential drag coefficients. A small field of view (30 cm x 30 cm) was used to obtain sufficient resolution near the wall to estimate the wall shear stress along the length of the array from the SPIV data. These results will be compared with the measured spatially averaged mean wall shear stress and the boundary layer momentum thickness estimations at the downstream end of the arrays determined from a control volume analysis. [Preview Abstract] |
Tuesday, November 22, 2005 12:06PM - 12:19PM |
NR.00006: Characteristics of the Mean Momentum Balance in Turbulent Boundary Layers With Favorable Pressure Gradient M. Metzger, A. Lyons, P. Fife The present study investigates the extent to which the layer structure of canonical wall flows, as observed by Wei et al.\ (2005) and Fife et al.\ (2005), becomes modified with the addition of a favorable pressure gradient. Experiments using an array of hot-wire probes were performed in a wind tunnel with a long development length. The pressure gradient was generated by tilting the ceiling at a constant angle. Well resolved hot-wire measurements are used to calculate the ratio of the terms in the mean momentum balance as a function of wall-normal distance, streamwise location, and Karman number. Data, from both the present experiments and available numerical simulations, are analyzed within the theoretical framework described by Metzger and Fife (submitted JFM), which predicts scaling properties based on a multiscale analysis of the mean momentum equation. Predictions from the theory, such as layer thicknesses, Reynolds stress decay, and peak Reynolds stress location, are evaluated using the aforementioned data. [Preview Abstract] |
Tuesday, November 22, 2005 12:19PM - 12:32PM |
NR.00007: Favorable Pressure Gradient Turbulent Boundary Layers: Part 1. Wall Shear Stress Calculations. Katherine Newhall, Raul Bayoan Cal, Brian Brzek, Gunnar Johansson, Luciano Castillo In order to improve the understanding of favorable pressure gradient turbulent boundary layers, near-wall measurements using 2D Laser Doppler Anemometry (LDA) are performed over a smooth surface. Observing the difficulties in obtaining the skin friction, alternate methods such as the momentum integral equation and the slope at the wall have been considered. The experiments include many downstream locations so that the momentum integral equation can be used to determine accurate values for u* and the skin friction. The various terms in the integrated momentum equation are continuously computed for each of the different cases which pertain to a set of upstream conditions. The development of the terms as the flow progresses downstream is of interest and is compared with experimental data previously obtained by Castillo and Johansson where upstream conditions are taken into account on zero pressure gradient boundary layers. [Preview Abstract] |
Tuesday, November 22, 2005 12:32PM - 12:45PM |
NR.00008: Favorable Pressure Gradient Turbulent Boundary Layers: Part 2. Effects of the Upstream Conditions on the Inner Flow Luciano Castillo, Raul Bayoan Cal, Katherine Newhall, Gunnar Johansson A low-Reynolds number experiment was conducted to study the upstream condition effects on the inner flow of a favorable pressure gradient (FPG) turbulent boundary layer. This was viable due to the use of 2-D laser-doppler anemometry (LDA) and analyzing the data using the equilibrium similarity analysis for pressure gradient turbulent boundary layers. Several upstream conditions were studied through the isolation of each particular condition in which a series of downstream traverses were taken. Conditions such as upstream wind-tunnel speed, trip-wire position and strength of pressure gradient were investigated. The velocity as well as turbulence quantities in the streamwise and wall-normal directions have been measured. Using the friction velocity obtained through the momentum integral equation, it was possible to normalize the mean velocity deficit and Reynolds stress profiles; thus obtaining information about how the inner flow was affected by the upstream conditions and the strength of pressure gradient. The argument is strengthened by comparing the data to an already performed experiment on the effects of upstream condition on smooth zero pressure gradient turbulent boundary layers in the same facilities carried out by Castillo and Johansson. [Preview Abstract] |
Tuesday, November 22, 2005 12:45PM - 12:58PM |
NR.00009: Prediction of Relaminarization on Favorable Pressure Gradient Turbulent Boundary Layers Raul Bayoan Cal, Xia Wang, Luciano Castillo Turbulent boundary layers subjected to favorable pressure gradients (FPG) tend to relaminarize when a sufficiently strong external pressure gradient is imposed on the flow. Traditionally, an acceleration parameter is used to predict relaminarization. Considering a wide array of existent data, it has been found that many quantities pertaining to the turbulent boundary layer provide information about the onset of relaminarization. On the verge of relaminarization, it is shown that the Reynolds stresses diminish drastically to nearly zero and the shape of the profile is different from other FPG profiles. Furthermore, the mean deficit velocity profiles are also found to be attenuated when scaled using the Castillo and George scaling, $U_\infty$, or the Zagarola and Smits scaling, $U_\infty \frac{\delta_*}{\delta}$. Also, further information is obtained through the examination of boundary layer parameters. Using similarity analysis, Castillo and George concluded that in order to achieve an equilibrium flow, the pressure parameter defined as, $\Lambda = -\frac{\delta}{U_\infty\frac{d\delta}{dx}}\frac{dU_\infty}{dx} = \frac{\delta}{\rho U_\infty^2\frac{d\delta}{dx}}\frac{dP_\infty}{dx}$ must be a constant; thus a power relation between the boundary layer thickness, $\delta$, and the free-stream velocity, $U_\infty$, exists. The power is given by the pressure parameter, $\Lambda$, as $\delta \sim U_\infty^{-1/\Lambda}$. Consequently, two quadrants have been found: one describing equilibrium and non-equilibrium FPG turbulent flows and a second quadrant describing relaminarized FPG flows. [Preview Abstract] |
Tuesday, November 22, 2005 12:58PM - 1:11PM |
NR.00010: Mesoscaling of Reynolds Shear Stress in Turbulent Channel and Pipe Flows Noor Afzal The present work deals with the exploration of prominent intermediate or mesolayer, in between traditional inner and outer layers. The Reynolds open equations of mean turbulent motion are analyzed by matched asymptotic expansions (MAE), for large Reynolds numbers. The multiscales analysis gives an additional intermediate or mesolayer in between traditional inner and outer layers, and condition for prominence of the mesolayer is analysed. The three layers asymptotic expansions in inner, meso and outer layer have been matched in two overlap domains by Izakson-Millikan-Kolmogorov hypothesis leading to open functional equations and whose functional solution contains some universal constants, which have been estimated from the extensive experimental data on fully developed turbulent channel and pipe flows. The prominent mesolayer has been analysed in terms of (i) width (in order of magnitude) (ii) Reynolds stress profile its maxima and its location as Reynolds number approaches infinity (iii) velocity profile in mesolayer domain (iv) time period of turbulent burst. The channel and pipe flow data of Zanoun (2003, Phd Thesis), DNS channel data Moser et al (1999, PoF) and pipe data of Toonder and Nieuwstadt (1997, PoF) along with several other data are analysed that supports the mesolayer theory. Comparison with Reynolds shear stress empirical relation of Panton (2005, AMR, 58,10), based on inner and outer layers giving very long expression for velocity profiles, is also presented. [Preview Abstract] |
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