九州大学 · 工学
ケネス・T・クリスティンセン教授の研究室は、流れの乱流構造、特に壁近傍におけるスパン方向渦運動やハリピン渦の三次元的構造を、粒子画像速度計測（PIV）を用いて高分解能で解明する研究を展開しています。特に、実際のタービンブレードに見られる不規則で多様なスケールの粗さが乱流構造に与える影響にも注力しており、実験的・数値的アプローチを融合した壁乱流の理解を深めています。時間分解能の高いPIV測定を活用し、小スケールの渦構造とその動的挙動を解明する点でも国際的に注目されています。
Figures are computed from collected data and may differ slightly.
The structure of velocity in the outer region of turbulent channel flow ( y + [gsim ] 100) is examined statistically to determine the average flow field associated with spanwise vortical motions. Particle image velocimetry measurements of the streamwise and wall-normal velocity components are correlated with a vortex marker (swirling strength) in the streamwise–wall-normal plane, and linear stochastic estimation is used to estimate the conditional average of the two-dimensional velocity field as
Particle image velocimetry experiments were performed to study the impact of realistic roughness on the spatial structure of wall turbulence at moderate Reynolds number. This roughness was replicated from an actual turbine blade damaged by deposition of foreign materials and its features are quite distinct from most roughness characterizations previously considered as it is highly irregular and embodies a broad range of topographical scales. The spatial structure of flow over this rough surface
Abstract The characteristics of a turbulent boundary layer overlying a complex roughness topography were explored with stereo particle-image velocimetry measurements in the wall-normal–spanwise $(y\mbox{--}z)$ plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials containing a broad range of topographical scales arranged in a highly irregular manner. The single-point turbulence statistics displayed strong spanwise heterogeneity, in
Time-resolved particle-image velocimetry measurements are made in the streamwise-wall-normal plane of turbulent channel flow at Re τ = 550 and 1747. Temporal and convective derivatives of velocity are computed from this data in order to evaluate the small-scale behaviour of these quantities as well as of the velocity itself. Instantaneous velocity fields indicate that the flow is dominated by small-scale vortex cores believed to be associated with hairpin/hairpin-like vortices. These vortices ha
The spatial signatures of retrograde spanwise vortices in wall turbulence are assessed from particle-image velocimetry measurements in the streamwise–wall-normal plane of a zero-pressure-gradient turbulent boundary layer at Re τ ≡ u * δ/ν=2350. The present results suggest that a proportion of retrograde spanwise vortices have a well-defined spatial relationship with neighbouring prograde vortices. Two-point cross-correlations and conditionally averaged velocity fields given a retrograde vortex r
Abstract We present an experimental study of pore‐scale flow dynamics of liquid CO 2 and water in a two‐dimensional heterogeneous porous micromodel, inspired by the structure of a reservoir rock, at reservoir‐relevant conditions (80 bar, 21°C). The entire process of CO 2 infiltration into a water‐saturated micromodel was captured using fluorescence microscopy and the micro‐PIV method, which together reveal complex fluid displacement patterns and abrupt changes in velocity. The CO 2 front migrate
Barchan dunes are three‐dimensional, crescent‐shaped bedforms found in regions of unidirectional flow and limited sediment supply, and while most commonly associated with aeolian environments, they have recently been observed in subaqueous domains and on the surfaces of Mars and Titan. As barchans migrate in the direction of the flow, they interact with their neighbors, typically by way of collision. The morphodynamics of such collision processes are complex, where the role of the turbulent flow
The spatial coherence of turbulent flow structures throughout the flow field associated with a collision between a smaller upstream barchan laterally offset from a larger downstream barchan is investigated using inhomogeneous, two‐point correlation coefficients of fluctuating streamwise velocity, from which the distribution, size, and orientation of the large‐scale motions in the flow are analyzed. Measurements were made with fixed‐bed models in a refractive‐index‐matched flume environment allow
Recent experimental and computational studies support the notion that the outer layer of wall turbulence is populated by hairpin-like vortices which tend to organize themselves into larger-sale coherent groups. The present effort attempts to evaluate the characteristics of this large-scale organization. Wide-field-of-view (2.5h × h) velocity fields are acquired by PIV in the streamwise-wall-normal plane of turbulent channel flow for 744 < Reτ < 2099 in order to study the imprint of this organiza
Abstract The pore‐scale flow of CO 2 and water in 2‐D heterogeneous porous micromodels over a C a range of nearly three orders of magnitude was explored experimentally. The porous geometry is a close reprint of real sandstone, and the experiments were performed under reservoir‐relevant conditions (i.e., 8 MPa and 21 °C), thus ensuring relevance to practical CO 2 operations. High‐speed fluorescent microscopy and image processing were employed to achieve temporally and spatially resolved data, pro
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