Drag Reduction of High Altitude Airships by Active Boundary Layer Control. Cusp Effect.

Bubbly turbulent drag reduction is a boundary layer effect.

In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to 4 x 10(5), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in...

Guidance, Navigation and Control of High-Altitude Airships

EXPERIMENTAL INVESTIGATION OF DRAG REDUCTION ON AHMED MODEL USING A COMBINATION OF ACTIVE FLOW CONTROL METHODS

Aerodynamic drag is an important factor in vehicles fuel consumption. Pressure drag which is the main component of total drag is a result of boundary layer separation from vehicle surface. Flow control methods are applied to avoid or at least delay separation. Depending upon whether these methods consume energy to control the flow or not, they are called active or passive control methods. In th...

URANS Study of Air-Layer Drag Reduction in a High- Reynolds-Number Flat-Plate Turbulent Boundary Layer

The air layer formation in a high Reynolds-number flat plate turbulent boundary layer is simulated using a two-phase sharp interface Cartesian grid solver. The interface is tracked by a coupled level set and volume-of-fluid method (CLSVOF) and turbulence is modeled by a Spalart-Allmaras (SA) turbulence model with a wall function (WF) approach. The air layer along the entire test plate is succes...

Drag reduction in a flat-plate turbulent boundary layer flow by polymer additives

This paper presents a theoretical study on the velocity distribution and the friction factor of boundary layer flows with polymer additives starting from the concept of “stress deficit.” A novel method of order of magnitude analysis is developed, which converts the governing equations of boundary layer flow into a solvable ordinary differential equation, thus the total shear stress distribution...