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Both open and closed loop control algorithms have been developed for manipulating wake flows past a solid cylinder in an electrically low-conducting fluid. The intent is to avoid vortex shedding and flow separation from the body, which is achieved through the introduction of localized electromagnetic forces (Lorentz forces) in the azimuthal direction generated by an array of permanent magnets and electrodes on the surface of the circular cylinder. The array of actuators offers the advantage of making the Lorentz force time and space dependent. More specifically, one closed loop control method has been derived from the equations of motion capable of determining at all times the intensity of the Lorentz force in order to control the flow. This is accomplished first, independently of the flow (open loop algorithm) and second, based on some partial flow information measured on the surface of the solid body (closed loop algorithm).

Micro-electro-mechanical systems (MEMS) thermal flow sensors featured with high spatial resolutions, fast frequency response and minimal interference with fluid flow have been applied widely in boundary-layer studies and aerodynamic flow sensing and control due to the inherent outstanding performances. In this study, MEMS thermal flow sensors were designed and fabricated on a flexible skin using the MEMS technology. The dimension of a single sensing element was 200 $\mu$m × 260 $\mu$m, which had a resistance of about 200 $\mathrm{\Omega }$ after annealing. By configuring thermal flow sensors in either a single thermal flow sensor and a thermal tuft sensor, separation points of a two-dimensional (2D) LS(1) 0417 airfoil at various angles of attack could be precisely detected. The experimental results show good agreement with the hot wire sensor and particle traced flow visualization in detecting the separation point on the suction surface of the airfoil.

Flow visualization in reciprocating flow inside branching tubes was performed to investigate the mechanism of axial gas exchange in the human lung system. A bronchial tube model is employed which is geometrically similar to the average human lung system. Water is used as the working fluid. The ranges of Reynolds and Womersley numbers in the present study correspond to those of normal human respiration and HFV (high frequency ventilation), respectively. It is revealed that the axial gas exchange phenomenon occurring in the human lung system is governed by a "trap-and-release" mechanism caused by the formation-and-destruction of the separation regions, which are formed on the wall of the parent tube and or daughter tubes, depending on the direction of the reciprocating flow.

The present investigation deals with a mathematical model representing the response of heat transfer to blood streaming through the arteries under stenotic condition. The flowing blood is represented as the suspension of all erythrocytes assumed to be Casson fluid and the arterial wall is considered to be rigid having differently shaped stenoses in its lumen arising from various types of abnormal growth or plaque formation. The governing equations of motion accompanied by the appropriate choice of the boundary conditions are solved numerically by Marker and Cell (MAC) method. The necessary checking for numerical stability has been incorporated into the algorithm for better precision of the results computed. The quantitative analysis carried out finally includes the respective profiles of the flow-field and the temperature along with their individual distributions over the entire arterial segment as well. The key factors like the pressure drop, wall shear stress, flow separation, Nusselt number and streamlines are examined for qualitative insight into the blood flow and heat transport phenomena through arterial stenosis. In conformity with other several existing findings the present simulation predicts that the pressure drop and Nusselt number diminishes with increasing yield stress values, and significant enhancement in values of Nusselt number is observed with increasing severity of the stenosis. However, the effect of the shapes of the stenoses on flow separation cannot be ruled out from the present investigation.

Combined effects of forced and natural convection on the occurrence of flow separation and heat transfer on a vertical paraboloid of revolution under the influence of a magnetic field are studied in this investigation. Inside the boundary layer, free convection is established due to the temperature difference between the fluid and the boundary while forced convection happens due to the presence of an external potential flow. The external potential velocity is chosen from the decelerated nature concerning the stream-wise coordinate due to which the flow separation is expected to occur. The influence of natural convection, the applied magnetic field, and the surface transverse curvature on delaying the flow separation and on the rate of heat transfer in the vicinity of the separation point is the aim of the investigation of this study. Regarding these important physical ingredients, the percentage increase in separation length and the rate of heat transfer are calculated. Moreover, their influence on the flow and heat-transfer phenomena has also been discussed in detail and presented through various graphs and tables. An exact numerical solution is obtained with the aid of an implicit finite difference scheme.

The characteristics of flow fields for a complete evolution of the non-breaking solitary wave, having a wave-height to water-depth ratio of 0.363 and propagating over a 1:5 sloping bottom, are investigated experimentally. This study mainly focuses on the occurrences of both flow separation on the boundary layer under an adverse pressure gradient and subsequent hydraulic jump with the abrupt rising of free surface during rundown motion of the shoaling wave, together with emphasis on the evolution of vortex structures underlying the separated shear layer and hydraulic jump. A flow visualization technique with particle trajectory method and a high-speed particle image velocimetry (HSPIV) system with a high-speed digital camera were used. Based on the instantaneous flow images visualized and/or the ensemble-averaged velocity fields measured, the following interesting features, which are unknown up-to-date, are presented and discussed in this study: (1) Flow bifurcation occurring on both offshore and onshore sides of the explicit demarcation curve and the stagnation point during runup motion; (2) The dependence of the diffuser-like flow field, being changed from the supercritical flow in the shallower region to the subcritical flow in the deeper counterpart, on the Froude number during the early and middle stages of rundown motion; (3) The positions and times for the occurrences of the incipient flow separation and the sudden rising of free surface of the hydraulic jump; (4) The associated movement and evolution of vortex structures under the separated shear layer, the hydraulic jump and/or the high-speed external main stream of the retreated flow; and (5) The entrainment of air bubbles from the free surface into the external main stream of the retreated flow.

Pulsatile flow of blood in a blood vessel having time-dependent shape (diameter) is investigated numerically in order to understand some important physiological phenomena in arteries. A smooth axi-symmetric cosine shaped constriction is considered. To mimic the realistic situation as far as possible, viscosity of blood is taken to be non-uniform, a shear-thinning viscosity model is considered and a physiologically relevant pulsatile flow is introduced. Taking advantage of axi-symmetry in the proposed problem, the stream function–vorticity formulation is used to solve the governing equations for blood flow. Effect of different parameters associated with the problem on the flow pattern has been investigated and disparities from the Newtonian case are discussed in detail.

Turbulent flow over rough boundaries is a common occurrence in nature and the subject of much interest in a range of disciplines. It has long been recognized that the geometry of the boundary (or surface) dictates the flow and turbulence structure on a mean and instantaneous time scale. However, the mechanisms linking flow characteristics to roughness geometry remain poorly quantified, which has implications for our understanding of a variety of processes, particularly those occurring in the near-boundary region. It has been demonstrated that temporal and spatial variations in flow structure are sensitive to a range of geometric parameters describing the boundary geometry. We review the experimental evidence for rough boundary/flow interactions across different disciplines. A synthesis reveals that (1) different approaches have led to the adoption of a variety of parameters that are used to describe boundary roughness, and (2) that different criteria are used to evaluate the relative effects of boundary roughness. Moreover, (3) much of the experimental data relates to idealized surfaces that do not reflect the complexity of natural boundaries, or (4) is taken in low Reynolds number flows, and generally cannot be applied to aquatic flows in nature. The implications for our understanding of near-bed aquatic processes in turbulent boundary layers are discussed, and suggestions for future research approaches are presented.

Mechanism of flow separation control by the micro or small devices such as plasma actuators is discussed based on a series of computations of low speed flows over an NACA 0015 airfoil with devices attached near the leading edge. The DBD plasma actuator is shown to be very effective for controlling flow separation at a Reynolds number of 6.3 × 10⁴. Flow attachment phenomenon induced by these devices is strongly related to the turbulent transition but the study reveals that it is not the only factor for the flow separation control. Analysis of the phase-average flow structures reveals that there exist remarkable structures in the flow near the airfoil surface, which characterizes the actuator-oriented flows to reduce flow separation.