Pair Of Longitudinal Vortices Research Articles

1930 可動渦発生器による縦渦と翼まわりの馬蹄形渦の干渉に関する研究(S21-6 噴流,後流及びはく離流れの流動解析と応用(6),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

1930 可動渦発生器による縦渦と翼まわりの馬蹄形渦の干渉に関する研究(S21-6 噴流,後流及びはく離流れの流動解析と応用(6),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

304 縦渦対と乱流後流の相互干渉に関する研究 : スケール比による影響(流体工学(1))

304 縦渦対と乱流後流の相互干渉に関する研究 : スケール比による影響(流体工学(1))

1937 固定及び可動渦発生器による縦渦対の相互作用に関する研究(S21-7 噴流,後流及びはく離流れの流動解析と応用(7),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The behavior of longitudinal vortex pair generated by active vortex generators and the interaction between the vortex pair were investigated by the measurement of three components of velocity with a rotating X-type hotwire anemometer. We can obtain the phase-averaged behavior of the vortex pair including the detail of the interaction process from the velocity, vorticity, and circulation data. The interaction between the vortex pair is dependent on the behavior of the VG trailing edge and the magnitude of the interaction affects the vorticity and circulation.

210 可動渦発生器による縦渦と干渉する馬蹄形渦に関する研究(1)(OS2-3 壁乱流の計測と制御,OS2壁乱流の計測と制御)

210 可動渦発生器による縦渦と干渉する馬蹄形渦に関する研究(1)(OS2-3 壁乱流の計測と制御,OS2壁乱流の計測と制御)

210 可動渦発生器による縦渦と干渉する馬蹄形渦に関する研究(2)(OS2-3 壁乱流の計測と制御,OS2壁乱流の計測と制御)

The periodic behavior of the horseshoe vortex interacting with a pair of longitudinal vortices by Active Vortex Generators (AVG) was discussed in the paper. The horseshoe vortex was generated at the base of NACA0024 and the longitudinal vortices were produced by AVG with the controlled yaw angle. The velocity was measured by using a rotary x-array hot-wire anemometer with a stepping motor. The objective is to clarify experimentally the phase-averaged characteristics of the velocity and the vorticity in the interference field between horseshoe vortex and longitudinal vortices. The Reynolds number Re_θ based on the momentum thickness was 1670. It was found that the horseshoe vortex was shifted by longitudinal vortex pair. The longitudinal vortices in Common Flow Up Case make the horseshoe vortex move forward the corner of the wing and has the effect of attenuate as to the vorticity in the downstream. In Common Flow Down Case, they merge into one vortex and their vorticity is decreased.

Visualization of longitudinal vortex flow in an enhanced heat transfer tube

Longitudinal vortex flow was visualized in an enlarged DDIR tube (discrete double inclined ribs on the inner surface). The experiments were conducted in a water tunnel using dye injection. Two kinds of ribs with different widths were investigated. The visualizations showed counter rotating longitudinal vortex pairs formed by the discrete double inclined ribs. The vortex intensity increased with increasing Reynolds numbers while the length over which the vortices were observed along the flow direction decreased with increasing Reynolds numbers for Re = 1000–2000. The vortex intensity and vortex flow length were also strongly affected by the rib dimensions.

An experimental study of the surface drift currents in a wave flume

The Lagrangian surface drift current induced by surface gravity waves in a wave flume has been investigated experimentally by the particle tracking method. It was observed that in most regions of the flume, the time-mean surface drift current was in the opposite direction to that of the wave propagation. The secondary current in the form of a pair of longitudinal vortices caused by the lateral boundaries was analyzed. It is suggested that the convection of the vorticity generated by the wave-absorber and the lateral boundaries is an important factor in the determination of the time-mean drift in a wave flume.

210 縦渦対と乱流後流の相互干渉における後流幅の影響(流体工学(2))

210 縦渦対と乱流後流の相互干渉における後流幅の影響(流体工学(2))

317 主流から導入した縦渦対と乱流境界層との干渉過程 : 秩序構造に及ぼす影響(流体工学III)

317 主流から導入した縦渦対と乱流境界層との干渉過程 : 秩序構造に及ぼす影響(流体工学III)

Large-Eddy Simulation of Transitional Boundary Layer with Impinging Shock Wave

The transition of a boundary layer on a flat plate with an impinging shock wave is studied numerically by compressible large-eddy simulation using a hybrid compact/Roe scheme. The numerical code is verified by comparison with experimental observations of shock wave/turbulent boundary-layer interaction and then applied for the analysis of shock wave/transitional boundary-layer interaction. The simulation provides accurate results with respect to the location of reattachment and the boundary-layer properties downstream of reattachment. Large-scale coherent structures such as longitudinal vortex pairs, low-speed streaks, and hairpin vortices are identified in the transitional region, and it is revealed that these coherent structures play important roles in the transition. Thus, it is important to resolve these structures adequately to obtain an accurate prediction of the reattachment point. The subsequent breakdown of these coherent structures have smaller length scales, and resolving the breakdown requires much finer grid resolution. However, the influence of underresolution of breakdown on the downstream flowfield can be largely ignored under the conditions examined. Large-eddy simulation is, therefore, useful for the qualitative analysis of flowfields involving a supersonic transitional boundary layer.

Numerical experiments on flapping foils mimicking fish-like locomotion

The results of numerical experiments aimed at investigating the topology of the vortex structures shed by an oscillating foil of finite span are described. The motion of the foil and its geometry are chosen to mimic the tail of a fish using the carangiform swimming. The numerical results have been compared with the flow visualizations of Freymuth [J. Fluids Eng. 111, 217 (1989)] and those of von Ellenrieder et al. [J. Fluid Mech.490, 129 (2003)]. The results show that a vortex ring is shed by the oscillating foil every half a cycle. The dynamics of the vortex rings depends on the Strouhal number St. For relatively small values of St, the interaction between adjacent rings is weak and they are mainly convected downstream by the free stream. On the other hand, for relatively large values of St, a strong interaction among adjacent rings takes place and the present results suggest the existence of reconnection phenomena, which create pairs of longitudinal counter-rotating vortices.

807 縦渦対と乱流後流の相互干渉に関する研究(OS8-2 複雑乱流の計測と制御(渦・はく離),OS8 複雑乱流の計測と制御,オーガナイズドセッション)

807 縦渦対と乱流後流の相互干渉に関する研究(OS8-2 複雑乱流の計測と制御(渦・はく離),OS8 複雑乱流の計測と制御,オーガナイズドセッション)

Turbulent Boundary Layer Distorted by a Longitudinal Vortex Pair Produced by a Delta-Wing with an Attack Angle (Reynolds Stress Profiles in a Symmetrical Plane)

An experimental investigation has been made on the Reynolds stress field in the interaction process between boundary layer and longitudinal vortex. Two types longitudinal vortex pair, namely common-flow up and common-flow down, were introduced into developed turbulent boundary layer from the free stream. Effect of the extra rate of strain, ∂W/∂z and ∂V/∂y, was examined in the profiles of three turbulent intensity components and Reynolds shear stress profiles. The boundary layer along symmetrical plane is classified into “cross flow” in case of cfd and “identifiable streamwise vortices” in case of cfu. The extra rates of strain modify magnitude of turbulent intensity and Reynolds shear stress in the inner layer in case of cfd. Otherwise, close to the wall in the case of cfu, local adverse pressure gradient is deduced from the fact that magnitude of transverse divergence is grater than that of spanwise convergence.

209 縮流による渦伸張を受けた縦渦対の挙動(流体工学(2))

209 縮流による渦伸張を受けた縦渦対の挙動(流体工学(2))

Time-Dependent Structures of a Two-Dimensional Turbulent Impinging Jet Accompanied by Longitudinal Vortex Paris

This article deals with an experimental observation of the longitudinal vortex pairs being formed intermittently in the stagnant region of an impinging jet from a viewpoint of selective enhancement of jet impingement heat transfer. A two-dimensional submerged water jet issuing from a convergent slot nozzle was made to impinge normally on a solid flat plate. Intermittent generation of the vortex pairs visualized by using a hydrogen bubble technique was recorded by a high-speed video camera. Large-scale turbulent structures were also observed in the stagnant region of an impinging jet with a Laser Doppler Velocimeter. A statistical analysis with conditional sampling was applied to extract each event of vortex-pair generation from the time-series of LDV velocity data as well as the time-series video images of visualized flow patterns. It has been found that the frequency of vortex-pair generation increases with nozzle-to-plate distance up to 6 nozzle widths. This tendency is coincident with that of the enhancement effect of jet impingement heat transfer depending on the jet development distance. It can be conjectured that those longitudinal vortex pairs appear owing to the wave instability of the shear vortex core filaments in the shear layer of the approaching jet.

縦渦対により撹乱を受けた二次元チャネル流 : 変形と弛緩過程(G.S. 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)

縦渦対により撹乱を受けた二次元チャネル流 : 変形と弛緩過程(G.S. 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)

Turbulent Boundary Layer Distorted by a Longitudinal Vortex Pair Produced by a Delta-Wing with an Attack Angle (Spanwise Variation of Mean Velocity Field)

An experimental investigation has been made on the interaction process between a boundary layer and longitudinal vortices. Comparable experimental conditions were set up for two types of vortex pair, namely, common-flow up (cfu) and common-flow down (cfd) and results obtained from two conditions were compared. The longitudinal vortex pair moves away from the wall in a faster rate in case of cfu. Spanwise spreading rate of two longitudinal vortex paths is larger in case of cfd. The decay of maximum longitudinal vorticity is slower in case of cfd. At the symmetrical plane between two vortices, the interaction between longitudinal vortex makes closely distributed mean velocity contour lines and higher skin-friction coefficient in case of cfd. Otherwise, in case of cfu the interaction makes widely distributed mean velocity contour lines and low skin-friction coefficient. Effect of extra rate of strain involved in momentum integral equation is applied to explain behaviors of boundary layer in the two cases.

横方向撹乱を加えた縦渦対と乱流境界層の干渉に関する研究(流体工学IX)

横方向撹乱を加えた縦渦対と乱流境界層の干渉に関する研究(流体工学IX)

主流中から導入した縦渦対により変形を受けた乱流境界層 : 対称面におけるレイノルズ応力分布(OS1-6噴流制御,噴流、後流及びせん断流の基礎と応用)

主流中から導入した縦渦対により変形を受けた乱流境界層 : 対称面におけるレイノルズ応力分布(OS1-6噴流制御,噴流、後流及びせん断流の基礎と応用)

NUMERICAL PREDICTION OF HEAT TRANSFER IN A CHANNEL WITH A BUILT-IN OVAL TUBE AND VARIOUS ARRANGEMENTS OF THE VORTEX GENERATORS

Three-dimensional flow structure in a rectangular channel with a built-in oval tube is quite complex due to the formation of horseshoe vortices near the front stagnation region of the tube and the Karman vortices behind it. The presence of a winglet pair in conjunction with the oval tube makes the flow structure even more complex. The interaction of the horseshoe vortices with the longitudinal vortices generated by the winglets and the interaction of the longitudinal vortices with the transverse Karman vortices culminate as a flow field dominated by the tangle of vortices. The existence of more than one pair of longitudinal vortices would further complicate the flow structure and the heat transfer behavior in the channel. The interaction between the secondary flows generated by the tube and by the winglets, as well as the interaction of the longitudinal vortices due to different arrangement of the winglets, play an important role in heat transfer enhancement. In the present article, effect of the streamwise as well as cross-stream location of the winglet pairs on heat transfer is investigated. For two pairs of winglets, possible configurations have been envisaged. All the possible arrangements have been investigated, and the optimal configuration has emerged.