Flow Around Three Side-by-Side Square Cylinders and the Effect of the Cylinder Oscillation

In this study, the flow field over three square cylinders (SCs) arranged side by side is investigated in a low-speed wind tunnel. The experiments are performed with three similar SCs for Reynolds number (Re) 295. The influences of spacing ratio on the wake size, drag coefficient, and flow interference of the cylinders are reported with the hotwire anemometry, particle image velocimetry (PIV), and the flow visualization techniques. Special attention is paid to the oscillation given to the middle cylinder and its effect on flow structure and related forces. The spacing ratio (s/D) ranges from 1.5 to 3, whereas the forcing frequency ratio ranges from 0.5 to 2 with amplitude of 10% of the cylinder width. It is observed that the spacing influences the flow structure, and the vortex shedding mechanism strongly. A secondary frequency appears in the flow field for spacing ratio s/D = 2 and 3. Depending upon the spacing ratios, the flow pattern is seen to be asymmetric biased, symmetric biased, and weakly interactive. The wake interaction decreases with increase in spacing ratios. With the oscillations, the wake becomes more unstable and complex. Additional wake oscillation frequency appears in the power spectra. With an increase in spacing ratios, the drag coefficient decreases, whereas with oscillations, higher drag force is observed compared to a stationary cylinder. A correlation is developed between the time-averaged drag coefficient with cylinder spacing and Reynolds number.

An Innovative Development of a Five-Hole Pressure Probe for Highly Unsteady Flow Phenomena

An advanced unsteady multi-hole pressure probe is developed in cooperation between the Chair of Aerodynamics and Fluid Mechanics of the Technical University of Munich, the probe manufacturer Vectoflow GmbH and the sensor producer fos4X GmbH. The application of additive manufacturing enables a wide variation in probe geometries. The spatial characteristics of the unsteady probe are determined in the aerodynamic calibration in a known steady uniform jet. Furthermore, the acoustic system inside the channels of the probe is investigated experimentally in the dynamic calibration. Both aerodynamic and dynamic calibration ensure an accurate reconstruction of the velocity components. Measurements of the near wake of a circular cylinder have been recorded with the unsteady probe and compared to data from the literature and corresponding hotwire anemometry measurements. Further improvements to enhance the range of applications of the probe have been initiated: This includes the miniaturization of the probe. Moreover, an unsteady differential fiber-optic sensor and its optic and passive measurement principle are introduced which shall improve the main dynamic specifications of the probe. By combining the additive manufactured pressure probe design and the novel fiber-optic sensor, more accurate measurements of high frequency flow phenomena are expected.

On the dynamics of three-dimensional slung prisms under very low and high turbulence flows

The distinctive pendulum-like oscillation and pitching patterns of cubic and rectangular slung prisms were inspected for two aspect ratios at various Reynolds numbers $Re$ under two free-stream turbulence levels. Systematic experiments were performed using high-resolution telemetry and hotwire anemometry to quantitatively characterize the dynamics of the prisms and the wake fluctuation. The results show that the dynamics of the prisms can be characterized by two distinctive regions depending on the prism shape. Specifically, in the case of cubic prisms the regions are defined by the growth rate of the pitching amplitude; whereas the dynamics of the rectangular prisms is more sensitive to the angle of attack. In particular, when the large side initially faces the flow, the regions are defined by the synchronization between the vortex shedding and pure oscillations under very low turbulence. When the smaller side initially faces the flow, the regions are defined by the equilibrium pitching position. Regardless of the geometry of the prism and flow condition the dominant oscillation frequency resulted as being close to the natural frequency of the small-amplitude pendulum-like oscillation.

THE DEVELOPMENT OF A MULTI-PURPOSE WIND TUNNEL

This manuscript contains the development stages of a multi-purpose wind tunnel built at the Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia. The fully automated wind tunnel is named Pangkor after an island in Perak, Malaysia. The development of the wind tunnel consists of three stages namely the design, fabrication and testing & commissioning. The computational fluids dynamic (CFD) approach was employed to ascertain the main geometries to optimize space utilization. Calculations are made based on typical wind tunnel design guidelines. Pitot tubes-pressure transducer, hotwire anemometry, temperature, room humidity and barometric sensors were used to verify actual flow of our construction. A traverse installed at the wind tunnel is capable of a two dimensional movements. The 15 kW axial fan used is especially selected because of space limitation. A variable frequency drive (VFD) connected to fan’s motor allows velocity control from a computer. All devices are connected a computer with one single controlling software; Scilab – ensuring ease of operation. The project shows that, with a limited budget, a wind tunnel with full functionalities could be constructed

Investigation of Spiral and Sweeping Holes

Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney-shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and square holes. A patent-pending spiral hole design showed the highest potential of the nondiffusion-type hole configurations. Velocity contours and flow temperature were acquired at discreet cross sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data were taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing ratios of 1.0, 1.5, 2.0, and 2.5 at a density ratio of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady Reynolds-average Navier–Stokes (RANS).

Investigation of Spiral and Sweeping Holes

Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing ratios of 1.0, 1.5, 2.0, and 2.5 at a density ratio of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.

Near Field Development of Planar Wakes Under the Effect of Asymmetric Initial Conditions

This paper reports an experimental investigation on the response of a planar wake past a flat plate to various upstream flow conditions. A tripping wire was placed on the upper side of the flat plate downstream the leading edge which resulted in asymmetric boundary layers. The near wake asymmetry was compared to their symmetrical counterpart at two different Reynolds numbers. The near wake dynamics were investigated using hotwire anemometry and flow visualizations. Self-similarity of the asymmetrical wakes was established. Asymmetry seemed to have the largest effect on the convection velocity of the large structures in the asymmetric laminar-turbulent wake.

Detailed Velocity and Turbulence Measurements in an Inclined Large-Scale Film Cooling Array

A large-scale model of an inclined row of film cooling holes is used to obtain detailed surface and flow field measurements that will enable future computational fluid dynamics code development and validation. The model consists of three holes of 1.9-cm diameter that are spaced three hole diameters apart and inclined 30 deg from the surface. The length to diameter ratio of the coolant holes is about 18. Measurements include film effectiveness using IR thermography and near wall thermocouples, heat transfer using liquid crystal thermography, flow field temperatures using a thermocouple, and velocity and turbulence quantities using hotwire anemometry. Results are obtained for blowing ratios of up to 2 in order to capture severe conditions in which the jet is lifted. For purposes of comparison with prior art, measurements of the velocity and turbulence field along the jet centerline are made and compare favorably with two data sets in the open literature thereby verifying the test apparatus and methodology are able to replicate existing data sets. In addition, a computational fluid dynamics model using a two-equation turbulence model is developed, and the results for velocity, turbulent kinetic energy and turbulent dissipation rate are compared with experimentally derived quantities.