Eran Arad

Control of Massive Separation on A Thick-Airfoil Wing: A Computational and Experimental Study

The objective of this research is mutual validation of computational analysis and experimental measurements of baseline and controlled flow over a blunt configuration. A rectangular wing with a 36 percent thick airfoil was selected as a test case, representing a rotor pylon fairing. However, the results are relevant to thick airfoils in general, and contribute to the study of turbulent boundary layer separation and control. Despite the apparently simple geometry, previous measurements on this NACA 0036 airfoil proved challenging for computational analysis. Computational analysis, using DES, provided accurate prediction of the the massive separation and the effects of the oscillatory flow control. Both the aerodynamic coefficients variation with angle of attack, and the pressure distribution on the wing were in good agreement with measurements. These results stand in contrast to the previous failure of incompressible RANS solutions to reproduce the massive separation, its effect on aerodynamic coefficients, and the impact of flow control from t different slots.

Flow Physics of Drag Reduction Mechanism using Suction and Pulsed Blowing

aft portion of the model. The drag reduction behavior was scaled using multiple AFC parameters associated with the unique features of the SaOB actuators. Results show that the drag reduction mechanisms associated with the SaOB actuation system include boundary layer suction, wall-jet momentum addition, unsteady shear layer excitation, thrust, and streamwise vortices.

Suction and Oscillatory Blowing Interaction with Boundary Layers

This work presents ongoing experiments toward developing fundamental understanding of suction and oscillatory blowing (SaOB) flow control mechanisms along with development of accurate and practical CFD simulation methodologies for complex unsteady active flow control systems. Experimental and computational studies were conducted on SaOB actuators’ internal flow and external interaction with two zero pressure gradient boundary layers. The experimental work incorporates detailed multi component hot-wire measurements of both laminar and turbulent boundary layers with steady suction and pulsed blowing for a single actuator and an array configuration. Large eddy simulation was employed for the computational model. Simulations were carried out on the actuator internal flow, and the resulting oscillatory blowing jet exit velocity profiles are characterized and fit with a functional form, in order to create simplified boundary conditions for future flow control simulations. Both experimental and computational results show that the suction hole geometry and configuration is an important factor in determining the structure and stability of the downstream laminar as well as turbulent boundary layer flow-fields. Measurements of oscillatory blowing jets interacting with a turbulent boundary layer demonstrate this flow control produces unsteady spanwise and streamwise vorticity components that can be interpreted as counter-rotating streamwise vortex patterns.

TOWARDS MORE ACCURATE ANALYSIS OF ACTIVE FLOW CONTROL ACTUATORS

Numerical and experimental analysis of synthetic jet actuator is reported. The study focuses on the actuator itself and on the vorticity field and structures that are generated by the actuator. Phase-locked, 2-D microscopic-PIV technique (MPIV) was used in experiment, and large eddies simulation (LES) was used for numerical analysis. The two methods were first validated for a circular steady jet, continuing with synthetic jet, emanated from a practical device design to quiescent air. The development of vortical structures and their interactions was carefully studied. The insight obtained is an important building block for better understanding of the interaction of synthetic jets and boundary layers. Nomenclature

Some Observations on Flame Propagation in Turbulent Combustion

A computational parametric study of turbulent combustion was conducted using LES. The study focuses on the complex phenomena of flame propagation and flame structure in a coaxial, gaseous fuel jet combustor. A new criterion for characterizing flame structure is suggested, providing the ability to quantify the flame three-dimensional structure, extinction, re-ignition and the overall spatial inhomogeneity in the combustor.

A Novel Approach for Design of In-flight Nose Release for a High Velocity Missile

A detachable missile nose was designed, tested and implemented in a new missile. This design enables the use of low-drag supersonic configurations for the major part of the flight, with the application of blunt seekers that are active during the end-game. The configuration of the ejected nose was designed using a novel approach, which included only a small amount of wind-tunnel experiments, coupled with an aerodynamic model produced by CFD. Simulation of flow dynamics coupled with rigid-body dynamics was developed and tested. Databases of aerodynamic forces and moments were produced using quasi-steady CFD, for hinged and free-flight nose, at very demanding conditions of supersonic flight and large angles of attack. These databases were used by rigid-body dynamic simulations, in one and six degrees-of-freedom modes, to predict the trajectories of the released nose.