In this review, we present control methods for flow over a bluff body such as a circular cylinder, a 2D bluff body with a blunt trailing edge, and a sphere. We introduce recent major achievements in bluff-body flow controls such as 3D forcing, active feedback control, control based on local and global instability, and control with a synthetic jet. We then classify the controls as boundary-layer controls and direct-wake modifications and discuss important features associated with these controls. Finally, we discuss some other issues such as Reynolds-number dependence, the lowest possible drag by control, and control efficiency.

Control of Flow Over a Bluff Body

An overview of modeling and experiments of vortex-induced vibration of circular cylinders

Natural ventilation of buildings is the flow generated by temperature differences and by the wind. The governing feature of this flow is the exchange between an interior space and the external ambient. Although the wind may often appear to be the dominant driving mechanism, in many circumstances temperature variations play a controlling feature on the ventilation since the directional buoyancy force has a large influence on the flow patterns within the space and on the nature of the exchange with the outside. Two forms of ventilation are discussed: mixing ventilation, in which the interior is at an approximately uniform temperature, and displacement ventilation, where there is strong internal stratification. The dynamics of these buoyancy-driven flows are considered, and the effects of wind on them are examined. The aim behind this work is to give designers rules and intuition on how air moves within a building; the research reveals a fascinating branch of fluid mechanics.

The fluid mechanics of natural ventilation

The editors have assembled a world-class group of contributors who address the questions the combustion diagnostic community faces. They are chemists who identify the species to be measured and the interfering substances that may be present; physicists, who push the limits of laser spectroscopy and laser devices and who conceive suitable measuremen

Applied Combustion Diagnostics

Increased concern for environment has led to the search for more environment friendly sources of energy. Wind energy can be a viable option in this regard. Vertical axis wind turbines offer promising solution for areas away from the integrated grid systems. However, they have certain drawbacks associated with different configurations. This paper reviews various configurations of VAWT along with their merits and demerits. Moreover, design techniques employed for VAWT design have also been reviewed along with their results. It was learned that coefficient of power (CP) for various configurations is different and can be optimized with reference to Tip Speed Ratio. Latest emerging design techniques can be helpful in this optimization. Furthermore, flow field around the blade can also be investigated with the help of these design techniques for safe operation.

Vertical axis wind turbine-a review of various configurations and design techniques

Observations of dynamic stall on Darrieus wind turbine blades

An experimental method for evaluating pressure field and fluid forces on a bluff body structure is studied using instantaneous velocity data measured by particle image velocimetry (PIV). This method solves a pressure Poisson equation numerically with the experimental velocity data by PIV. The measurement of the velocity field around a circular cylinder is carried out using two CCD cameras placed side by side, which allows simultaneous measurement of velocity near and far field around the circular cylinder. The pressure and fluid forces on the stationary cylinder evaluated by this method agree closely with those in the literature, suggesting the validity of this technique. The present technique is also applied to a circular cylinder with rotational oscillation at Reynolds number 2000. It is found that the drag force on a circular cylinder is magnified at low-frequency oscillation and reduced at high-frequency oscillation. The drag coefficient at high-frequency oscillation is reduced by 30% with respect to the stationary cylinder, while the fluctuating lift is slightly increased due to the generation of synchronized vortex shedding at high-frequency oscillation.

https://iopscience.iop.org/article/10.1088/0957-0233/16/4/011/pdf

Evaluation of pressure field and fluid forces on a circular cylinder with and without rotational oscillation using velocity data from PIV measurement

In this present paper, a method for simultaneously measuring the temperature and the velocity in a planar cross-section of fluid flow with a colour CCD camera is described. This technique combines the laser-induced fluorescence (LIF) and particle image velocimetry (PIV). The temperature is evaluated by the two-colour LIF technique using red and green images of the colour CCD camera, while the velocity is obtained from two sequential blue images by PIV. It is found that the temperature sensitivity of the present technique is almost the same as that of the standard two-colour LIF technique by two monochrome CCD cameras with optimum filter setting, but it provides a simple and convenient system for simultaneous measurement of temperature and velocity in thermal flows. The uncertainty in the temperature measurement is found to be a function of concentration ratios of the fluorescent dyes in the two-colour LIF technique and it increases with an increase in the number of tracer particles for velocity measurement. This technique is successfully applied to the simultaneous measurement of temperature and velocity in the turbulent buoyant plume. The statistical properties of the plume, such as mean and turbulence characteristics of the plume as well as turbulent heat fluxes are evaluated in the initial region of the buoyant plume.

https://iopscience.iop.org/article/10.1088/0957-0233/15/5/030/pdf

Simultaneous measurement of temperature and velocity using two-colour LIF combined with PIV with a colour CCD camera and its application to the turbulent buoyant plume

Nobuyuki Fujisawa

Papers

Observations of dynamic stall on Darrieus wind turbine blades

Evaluation of pressure field and fluid forces on a circular cylinder with and without rotational oscillation using velocity data from PIV measurement

Simultaneous measurement of temperature and velocity using two-colour LIF combined with PIV with a colour CCD camera and its application to the turbulent buoyant plume

Experimental study on flow and noise characteristics of NACA0018 airfoil

Flow control around a circular cylinder by internal acoustic excitation