Project 2: Study of Separated Flow in a Low- Pressure Turbine* Joshua Combs, Aerospace Engineering, Junior, University of Cincinnati Devon Riddle, Aerospace Engineering, Senior, University of Cincinnati ASSISTED BY: Michael Cline, Graduate Research Assistant Dr. Kirti Ghia, Faculty Mentor *Sponsored by the National Science Foundation Grant ID No. DUE

Project Goals Goal 1: Goal 1: Understand the phenomenon of flow separation on streamlined bodies. Goal 2: Goal 2: Understand methodologies for analyzing and controlling flow separation. 2

Objectives Objective 1: Objective 1: Investigate characteristics of the low-pressure turbine. Objective 2: Objective 2: Explore methods of flow separation and control. Objective 3: Objective 3: Disseminate findings in a technical report. 3

Motivation Reduce engine weight (COST!!) i.e. use fewer blades Increases the amount of work done by each blade Adverse pressure gradient and low Reynolds number induces flow separation thereby decreasing low-pressure turbine (LPT) efficiency Must CONTROL flow in LPT to reduce flow separation 4

Terminology Adverse Pressure Gradient (APG): Pressure increases in the flow direction Flow Separation: Detachment from body surface Michael Cline, 2012 AY- REU Program 5 John Anderson, Fundamentals of Aerodynamics, 5th

Terminology continued Reynolds Number (Re): Dimensionless quantity representing the ratio of inertial forces to viscous forces Indicates whether flow is laminar or turbulent Re ≈ 10e5 Re ≈ 10e6Transition Region: Zone between laminar and turbulent flow Boundary Layer (BL): Thin viscous region adjacent to the body 6 John Anderson, Fundamentals of Aerodynamics, 5th

Flow Control Methods Two main categories: Passive i.Trip Wire ii.Vortex Generators iii.Roughness …There are others, these are just to name a few Active i.BL Suction ii.Synthetic Jet iii.Plasma Actuator 7

Passive Control Tripwire Promotes transition from laminar BL to turbulent BL Increases momentum to overcome APG (Top-Bottom): “Drag Reduction on Aerodynamic Shapes with Ground Effect”, on/aerodynamics/q0228.shtml Vortex Generator “Re-energizes” BL Delays flow separation 8

Active Control Adds momentum through a body force. Proven to reattach flow effectively; no fluid injection Plasma Actuators 9 Professor Wei Shyy University of Michigan

Types of Plasma Actuators Single Dielectric Barrier Discharge (SDBD) Plasma Actuators Glow Discharge Actuators Plasma Synthetic Jet Actuators 10

Single Dielectric Barrier Discharge Plasma Actuators Widely utilized Desirable features for use in air at atmospheric pressures – Active airfoil leading edge separation control – Control airfoil dynamic stall – Bluff body flow control – Boundary layer flow control Internal and external flow applications. Effective at high subsonic, transonic, and supersonic Mach numbers Two electrodes separated by dielectric barrier material. One electrode on aerodynamic surface exposed to air Covered electrode encapsulated in dielectric material Voltage is applied igniting the DBD Unique: sustain large volume discharge at atmospheric pressure without arcing. Self limiting. Flow control created through generated body force vector field mixing with the external flows momentum. 11

Experiment using SDBD actuators Cylinder Side image of the smooth flow closely attached to the cylinder. Close up on the flow behind the cylinder. Wake is minimized. 12 Professor Wei Shyy University of Michigan

Experiment using SDBD actuators continued Cylinder Side image of flow without the use of SDBD. Close up on the flow behind the cylinder. Wake is large and out of control. 13 Professor Wei Shyy University of Michigan

Plasma Synthetic Jet Actuator Designed for flow control that consists of an annular electrode in quiescent and flat plate boundary layer flows. SJA formed from the working flow of the system Name came from: – Circular plasma region produced on the actuation generates vertical zero-net mass flux (synthetic) jet. Actuator pulses forming a starting vortex ring. Advects ahead of jet and secondary vortex rings near actuator surface. Pulsing frequency is varied, creating multiple vortex rings Vortex ring interactions – Increases peak velocity – Increases streamwise extent of the jet. 14

Experiment using Synthetic Jet Actuators Investigating plasma actuators and synthetic jets to develop a plasma flow control device that is more effective. Observed varied pulse frequencies and jet characteristics Peak velocity Steady operation of the actuator without pulse frequencies Constant velocity 15

Experiment using Synthetic Jet Actuators continued Both graphs show the streamwise distribution of local maximum mean axial velocity Peak velocity pulsing at 10 Hz Optimum time of operation is less than 24 ms Interesting observation being that it never returns to zero velocity Suggests optimum operational frequency closer to 10 Hz. 16

Computational Fluid Dynamics Method of analyzing fluid mechanics with theoretical and experimental techniques Utilizes algorithms and numerical methods to solve and analyze fluid flow problems Computer carries out the calculations of time dependent interactions between the body and the fluid 17

Generate “baseline” results for the LPT Learn how to model flow and implement into ANSYS Fluent (CFD software) Learn to used programming languages required for CFD (i.e. C++) 18 …Future Work

Timeline Weeks: Learn characteristic s of turbine Understand flow separation Understand transition of flow Study flow control strategies Poster Final Report Journal Paper Due Final Day 19

Questions?

References Huan, Junhui, Separation Control Over Low Pressure Turbine Blades Using Plasma Actuators, University of Notre Dame, Hilbert, Brian F., Drag Reduction on Aerodynamic Shapes with Groudn Effect, Clarkston University, Xiaoping Xu, Zhou Zhou, Ruijun Fan, Junli Wang, Investigation of Active Flow Control on Aerodynamic Performance of HALE UAV Airfoil, Second International Conference on Computer Modeling and Simulation, Shin, J., Narayanaswamy, V., Raja, L.L., Clemens, N.T., "Characterization of a Direct-Current Glow Discharge Plasma Actuator in Low-Pressure Supersonic Flow," AIAA Journal, Vol. 45, No. 7, pp , 2007.