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Jake_Mitchell - Design of a “Hinged” Delta Wing to...

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Unformatted text preview: Design of a “Hinged” Delta Wing to Control Vortex Flow Wing By: Jake Mitchell 12/13/03 I. Introduction I. Delta wings have Delta leading-edge vortices over the surface over It may be desirable to It control the size and strength of these vortices vortices I. Introduction I. Changing the size and Changing strength of a vortex may change how it breaks down down Early vortex breakdown Early can be desirable because an aircraft can follow in its wake more closely wake Early vortex breakdown Early can also be undesirable because if it breaks down over the wing, it can decrease lift decrease I. Introduction I. Some devices used to control vortex breakdown: – Mechanical Devices: strakes, canards, fillets, leadingedge extensions, flaps, vortex fences – Pneumatic devices: suction applied downstream of Pneumatic vortex breakdown stabilizes vortex; blowing also shifts the vortex breakdown location downstream the Delaying vortex breakdown causes aircraft to be Delaying able to perform at higher angles of attack able II. Proposed Design II. Does creating a ‘hinge’ near the vortex line affect the Does vortex size, strength, or breakdown? vortex Does the hinged part affect wing performance? Bend outboard section up and down, and see what the Bend overall affect is overall II. Proposed Design II. • Modeling an actual wing with a hinge proved Modeling to be very difficult. to • An approximation was used: very simplified An delta wing design delta • The overall effects on the simplified delta The wing will likely happen on a normal delta wing wing II. Proposed Design II. Model was created in Model Gambit by defining vertices: a ‘triangular’ airfoil was used airfoil A tapered triangular mesh tapered was used was II. Proposed Design II. To capture vortex flow To across surface of wing, a nonlinear code must be used be In this design, Fluent In 6.0 was used. Fluent solves the full nonsolves llinear Navier-Stokes inear equations equations III. Solution III. Solution methods: – Pressure: standard algorithm – Pressure-velocity coupling: SIMPLE algorithm Pressure-velocity (3rd order accurate) (3 – Momentum: 2nd order upwind – Modified turbulent viscosity: 2nd order upwind 1st order upwind is too diffusive for an accurate answer accurate Most grids had ~117,000 cells in them III. Solution III. Turbulence model: Spalart-Allmaras – One-equation model – An equation is derived for the eddy viscosity An from scratch and then taylored for aerodynamic flows flows – S-A model is diffusive, but it is better (and S-A quicker) than k-ε model quicker) model III. Solution III. Geometry settings: – – – – Root chord: 15 meters 30-degree sweep Hinge line is at 20 degrees of sweep Thickness at chord trailing edge: 1 meter Velocity: 150 m/s at 15 degrees angle of attack Standard atmosphere temperature and pressure III. Solution III. Base wing with no hinge (to compare others with) Solution was allowed to converge for a first order accurate solution; Solution then was continued until convergence with a second-order solution then Residuals show how quickly solutions converged Baseline converged after ~210 iterations total All wings have same geometry except for the hinge angle III. Solution III. -15 degree case Converged after ~290 Converged iterations iterations III. Solution III. -30 degree case Did not converge even after Did almost 1,700 iterations almost Came close enough that we can Came assume it is fairly accurate assume III. Solution III. +15 degree case Converged after ~245 Converged iterations iterations III. Solution III. +30 degrees case Solution converged Solution after ~215 iterations after III. Solution III. Problem: base wing Problem: produces negative lift! produces Contours of pressure Contours confirm this confirm Pressure is negative on Pressure lower surface, and positive on upper surface on Shown is a case run at 30 Shown degrees angle of attack, with the base wing with IV. Analysis IV. Graphs of pressure Graphs coefficient on wing section also confirm that we have downforce instead of lift Shown are -30 deg, 0 deg, Shown and + 30 deg; the pressure distribution ‘closes’ as the angle increases angle Using an actual airfoil Using section would probably have prevented this have IV. Analysis IV. Baseline case is shown above First image is vortex at 10 meters aft of the leading edge Second image is vortex at 10 meters aft of the trailing edge, which can Second be considered the ‘near wake’ be Images are contours of relative z-velocity, or velocity in the spanwise Images direction direction All z-velocity graphs have the same range of values for comparison IV. Analysis IV. Wing with -30 degree hinge Vortices are very large on the wing In the wake, vortices are taking a long time to In break down break IV. Analysis IV. Wing with -15 degree hinge Vortices decrease on the wing as the angle is Vortices increased increased In the wake, the vortex is breaking down quicker IV. Analysis IV. Baseline (0 degree) case again (for visualization Baseline continuity purposes) continuity IV. Analysis IV. Wing with +15 degree hinge Vortex loses strength and size on surface of wing Vortex breaks down rapidly behind wing IV. Analysis IV. Wing with +30 degree hinge Flow over the wing surface is complex In the wake, vortices are lasting longer IV. Analysis IV. 70000 60000 50000 Drag Force [n] 40000 30000 20000 10000 0 -40 -30 -20 -10 0 10 20 30 40 10 20 30 40 Tip Angle [deg] Lift vs. Tip Angle 150000 100000 50000 0 -40 Lift Force [n] What about the forces What on the wing? on Minimum drag is when Minimum the angle is zero the Maximum lift is Maximum obtained when the angle is the highest angle We get positive lift We when the angle is sufficiently high sufficiently Drag vs. Tip Angle -30 -20 -10 0 -50000 -100000 -150000 -200000 -250000 Tip Angle [deg] IV. Analysis IV. Lift over Drag Ratio Lift also increases as the hinge angle increases hinge L/D for different tip angles 2 1 0 L/D -40 -30 -20 -10 0 -1 -2 -3 -4 Tip Angle [deg] 10 20 30 40 IV. Analysis IV. The cause for the The increase in performance: the hinged part of the wing gets loaded up more gets This may be bad from This a structural point of view view IV. Analysis IV. Possible sources of error – Grid may not be refined enough – possible to do a grid Grid refinement study refinement – Turbulence modeling used – only way to get around this Turbulence is to do a Direct Numerical Simulation (DNS), which is extremely costly. Possible to use a more accurate turbulence model, however. turbulence – Convergence criterion set relatively high, to allow for Convergence quick convergence. For a full design study, the convergence criterion would be much lower. convergence V. Conclusion V. Decreasing the hinge angle causes poorer Decreasing performance and stronger vortices in the wake wake Increasing the hinge angle increases Increasing performance and causes the vortices in the wake to break down quicker, to a point. wake The hinged portion of the wing receives high The aerodynamic loads, which can destroy the hinges if not taken into consideration hinges V. Conclusion V. Possible uses for a hinged delta wing: – Allow the wake behind an aircraft to diminish Allow more quickly so that other aircraft can take off after it or fly in formation behind it after – Increase drag while braking – Increase L/D while taking off – By hinging one wing, a rolling moment is By created created ...
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