The Aerodynamics of Low Sweep Delta Wings Jose M. Rullan Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Engineering Mechanics Dr. Demetri P. Telionis, Chair Dr. Scott Hendricks Dr. Ronald Kriz Dr. Saad Ragab Dr. Pavlos Vlachos April 21, 2008 Blacksburg, Virginia Keywords: low sweep delta wings, streamwise vortex, vortex breakdown, flow control, three-dimensional actuation Copyright 2008, Jose M. Rullan The Aerodynamics of Low Sweep Delta Wings Jose M. Rullan Abstract The aerodynamics of wings with moderately swept wings continues to be a challenging and important problem due to the current and future use in military aircraft. And yet, there is very little work devoted to the understanding of the aerodynamics of such wings. The problem is that such wings may be able to sustain attached flow next to broken-down delta-wing vortices, or stall like two-dimensional wings, while shedding vortices with generators parallel to their leading edge. To address this situation we studied the flow field over diamond-shaped planforms and sharp-edged finite wings. Possible mechanisms for flow control were identified and tested. We explored the aerodynamics of swept leading edges with no control. We presented velocity and vorticity distributions along planes normal and parallel to the free stream for wings with diamond shaped planform and sharp leading edges. We also presented pressure distributions over the suction side of the wing. Results indicated that in the inboard part of the wing, an attached vortex can be sustained, reminiscent of delta-wing type of a tip vortex, but further in the outboard region 2-D stall dominated even at 13° AOA and total stall at 21° AOA. To explore the unsteady flow field and the effectiveness of leading- edge control of the flow over a diamond-planform wing at 13° AOA, we employed Particle Image Velocimetry (PIV) at a Reynolds number of 43,000 in a water tunnel. Our results indicated that two-D-like vortices were periodically generated and shed. At the same time, an underline feature of the flow, a leading edge vortex was periodically activated, penetrating the separated flow, eventually emerging downstream of the trailing edge of the wing. To study the motion and its control at higher Reynolds numbers, namely 1.3 x 106 we conducted experiments in a wind tunnel. Three control mechanisms were employed, an oscillating mini-flap, a pulsed jet and spanwise continuous blowing. A finite wing with parallel leading and trailing edges and a rectangular tip was swept by 0°, 20°, and 40° and the pulsed jet employed as is control mechanism. A wing with a diamond-shaped-planform, with a leading edge sweep of 42°, was tested with the mini- flap. Surface pressure distributions were obtained and the control flow results were contrasted with the no-control cases. Our results indicated flow control was very effective at 20° sweep, but less so at 40° or 42°. It was found that steady spanwise blowing is much more effective at the higher sweep angle. iii Dedication To the two people that trust me more than I trust myself, my wife Mari and my son Miguel Antonio. The sacrifice was worth doing. iv Acknowledgements I would like to express my most sincere appreciation to my advisor, Dr. Demetri Telionis. Your support, encouragement and dedication to this job and to my wellbeing were unmatched. I would not be completing these requirements if it were not for you. For all these I am extremely grateful. I need to express my appreciations to my other committee members. Dr. Pavlos Vlachos, your advice and comments are welcomed. Dr. Saad Ragab, thanks for being always there when any question arises. A visit to your office is another class session. Dr. Hendricks and Kriz, thank you for accepting and submitting yourself to my performances. To all my friends in the Fluids Lab, you made spending the days in the lab easier. I need to recognize Jason Gibbs who found the time to be spent when he did not needed to. Ali Etebari for always being helpful and at hand whenever work had to be done. Thanks to Dr. Matt Zeiger for all his ideas, input, and advice in this research. I also appreciate the efforts and advice put on by the ESM Shop personnel. Both David Simmons and Darrel Link are extremely diligent. Last, to my family, whose encouregment and unconditional love made possible all the years spent here. v Table of Content Abstract.............................................................................................................................. ii Dedication ......................................................................................................................... iv Acknowledgements ........................................................................................................... v List of Figures.................................................................................................................viii 1. Introduction............................................................................................................... 1 1.1 Separated flow and Vortex breakdown............................................................... 2 1.2 Flow control........................................................................................................ 4 1.2.1 Mechanical Flaps........................................................................................ 6 1.2.2 Periodic blowing......................................................................................... 7 1.2.3 Other actuations.......................................................................................... 8 1.3 Methodology....................................................................................................... 9 1.4 Dissertation Structure........................................................................................10 1.5 References......................................................................................................... 11 2. Experimental Setup And Equipment.................................................................... 15 2.1 Introduction....................................................................................................... 15 2.2 Wind tunnels..................................................................................................... 15 2.2.1 ESM wind tunnel....................................................................................... 15 2.2.2 Virginia Tech Stability wind tunnel .......................................................... 16 2.3 Wind tunnel models .......................................................................................... 17 2.3.1 Model A..................................................................................................... 17 2.3.2 Model B..................................................................................................... 20 2.3.3 Data Acquisition system............................................................................ 21 2.4 Water Tunnel.................................................................................................... 22 2.5 Water Tunnel Model......................................................................................... 23 2.6 Particle Image Velocimetry System.................................................................. 25 2.7 Uncertainty analysis for data taken during this effort....................................... 27 2.7.1 Uncertainty analysis for the pressure coefficients.................................... 27 2.7.2 Uncertainty Analysis for Velocities Measured with PIV .......................... 28 2.8 References......................................................................................................... 29 3. The Aerodynamics of Diamond-Shaped-Planform Wings.................................. 31 3.1 Introduction....................................................................................................... 31 3.2 Facilities, Models and Equipment..................................................................... 33 3.2.1 Facilities and Models................................................................................ 33 3.2.2 Particle Image Velocimetry ...................................................................... 35 3.2.3 Sensors and Actuators............................................................................... 37 3.3 Results and Discussion..................................................................................... 38 3.3.1 Flow Visualization and PIV Results ......................................................... 38 vi 3.3.2 Pressure Distributions and Wake Trefftz Plane Results........................... 44 3.4 Conclusions....................................................................................................... 50 3.5 References......................................................................................................... 50 4. Flow Control over Diamond-Shaped-Planform Wings with Sharp Edges. Velocity and Vorticity Fields.......................................................................................... 53 4.1 Introduction....................................................................................................... 53 4.2 Facilities, Models and Equipment..................................................................... 55 4.2.1 Facilities and Models...............................................................................