Investigation of Local Scour around L-Shape Submerged Groynes in Clearwater Conditions

Submerged Groynes are low profile linear structures that are generally located on the outside bank to form Groynes fields and prevent the erosion of stream banks by redirecting high-velocity flow away from the bank. This research was studied in detail through two major stages. The first stage of the study is based on laboratory experiments to measure the development of local scour around L-shape submerged Groyne with the time, and special attention is given to the effects of different hydraulic and geometric parameters on local scour. Also; maps were drawn showing contour lines that represented the bed levels for maximum scour depth after reaching the equilibrium case. The result showed that a decrease in the scour depth ratio due to the increasing submerged ratio, and the number of Groynes. While the scour hole geometry will increase with the Froude number, flow intensity, and the spacing between Groynes, the decreasing percentage in the scour hole was measured to be about (4.3) % and (4.4) % for decreasing the spacing between Groynes from (2Lg) to (1.5Lg). Besides, it was range about (11.1) % and (14.0) % when reducing the spacing from (1.5Lg) to (Lg) under the same value of maximum Froude number. The second stage of the study is based on experimental results. A new formula was developed by using statistical analysis and it was found that a good determination coefficient.

Optimal motion control of three-sphere based low-Reynolds number swimming microrobot

Microrobots with their promising applications are attracting a lot of attention currently. A microrobot with a triangular mechanism was previously proposed by scientists to overcome the motion limitations in a low-Reynolds number flow; however, the control of this swimmer for performing desired manoeuvres has not been studied yet. Here, we have proposed some strategies for controlling its position. Considering the constraints on arm lengths, we proposed an optimal controller based on quadratic programming. The simulation results demonstrate that the proposed optimal controller can steer the microrobot along the desired trajectory as well as minimize fluctuations of the actuators length.

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

As technology advances, rotating machinery are operating at higher rotational speeds and increased pressures with greater heat concentration (i.e. smaller and hotter). This combination of factors increases structural stresses, while increasing the risk of exceeding temperature limits of components. To reduce stresses and protect components, it is necessary to have accurately designed thermal management systems with well-understood heat transfer characteristics. Currently, available heat transfer correlations operating within high Taylor number (above 1×10^10) flow regimes are lacking. In this work, the design of a high Taylor number flow experimental test rig is presented. A non-invasive methodology, used to capture the instantaneous heat flux of the rotating body, is also presented. Capability of the test rig, in conjunction with the use of high-density fluids, increases the maximum Taylor number beyond that of previous works. Data of two experiments are presented. The first, using air, with an operating Taylor number of 8.8± 0.8 ×10^7 and an effective Reynolds number of 4.2± 0.5 ×10^3, corresponds to a measured heat transfer coefficient of 1.67 ± 0.9 ×10^2 W/m2K and Nusselt number of 5.4± 1.5×10^1. The second, using supercritical carbon dioxide, demonstrates Taylor numbers achievable within the test rig of 1.32±0.8×10^12. A new correlation using air, with operating Taylor numbers between 7.4×10^6 and 8.9×10^8 is provided, comparing favourably with existing correlations within this operating range. A unique and systematic approach for evaluating the uncertainties is also presented, using the Monte-Carlo method.

Experimental investigation on flow structures of steadily translating low-aspect-ratio wings in low Reynolds number flow

In recent decades, Micro Air Vehicles (MAVs) have been a hot topic for their promising future. But the promotions of MAVs are hindered by their short endurances. To solve this problem, inspirations are brought from migratory butterflies who utilize the ‘flapping-gliding’ skill during long-distance migration to improve the flight efficiency. The butterfly’s gliding flights, which can be simplified by considering the steadily translating fixed wings, have drawn high attentions. Previous studies mainly focus on the aerodynamics of the low-aspect-ratio fixed wings at Re ≈ 105 via force measurements. However, few experimental studies have measured the 3D flow fields. Consequently, the underlying high lift-to-drag ratio mechanisms in the steadily translating butterfly-shaped wings are still not clear. To shed new light on this problem, the 3D flow structures around butterfly-shaped wings were captured and investigated in detail.