Injection of a non-Newtonian fluid to improve the hydrofoil performance

Abstract

In this study, an active flow control method based on the injection of a non-Newtonian (NN) fluid through a slot on the suction side of a hydrofoil is proposed. The viscosity of several NN fluids including the Power-law, Carreau, Cross, Ellis, and Prandtl-Eyring are discussed and compared here. Besides NN fluids, the water as a Newtonian fluid is also employed in simulations to compare the efficiency of NN fluids against Newtonian ones. The governing equations are the two-phase Navier-Stokes equations that are numerically solved using the finite volume method with the Volume of Fluid (VoF) model to capture the interface of two fluids. This numerical solver used is examined by comparing its results with the experimental data for the fluid flow past NACA 0012 and NACA 0018 at the angles of attack , and Reynolds number is . This comparison shows that this numerical method used can reasonably compute the hydrofoil performance parameters including the lift coefficient, drag coefficient, and lift-to-drag ratio. When there is no injection, the water can be replaced with a NN fluid to figure out how changing the surrounding/primary fluid can affect the hydrodynamic performance of NACA 0012. In general, results indicate that the hydrofoil immersed in a NN fluid attains better performance. Moreover, while the surrounding fluid is assumed to be the water, the effect of injecting/blowing fluid which is either the water or NN fluid on the NACA 0012’s performance is investigated here. Besides, the effect of momentum coefficients , , and  is also studied. Indications are that injection of the water is not a suitable way to improve the hydrodynamic performance of the hydrofoil at a moderate angle of attack. Furthermore, injection of the water at  is not suggested because the hydrofoil performance deteriorates, but at higher momentum coefficients like  the hydrofoil performance is improved at the stall point and beyond that. Contrary to the water case, the NN fluid is still effective for low momentum coefficient values. Indeed, the hydrofoil achieves better hydrodynamic performance for all the momentums coefficients in comparison with cases without the injection and injection of the water. The effect of the change of the NN fluid from the Carreau to the Prandtl-Eyring NN fluid is also examined, and conclusions are that the Prandtl-Eyring NN fluid is more successful in enhancing the hydrofoil performance and it can be preferred against Carreau fluid. Finally, the effect of the thickness of a hydrofoil on the efficiency of this active flow control method is studied. Observations indicate that injection of NN fluids can significantly improve the hydrodynamic performance of NACA 0012 and NACA 0018, however, it has much impact on the performance of a thicker hydrofoil which is NACA 0018 here. Therefore, this active flow control method based on injection of NN fluids is a reliable and effective method to mitigate unsteadiness, delay the stall, increase the lift coefficient, and decrease the drag coefficient, and finally, it can be considered as a suitable alternative method for other flow control techniques in hydrodynamic applications.