vspaeromodeling

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 vspaeromodeling [2015/07/02 10:48]blitherland vspaeromodeling [2018/04/01 14:41] Line 1: Line 1: - ====== Modeling for VSPAERO ====== - [[start|Back to Landing Page]] - [[vspaerotutorial|VSPAERO Tutorial]] - VSPAERO will analyze almost any geometry as long as the components are **closed**. ​ Whether you are able to obtain meaningful, or reliable, information is another story. ​ There are limits to VSPAERO'​s abilities to converge toward what you may think is the "​right"​ answer for a given set of flow conditions. ​ Keep in mind that this is a linear solver. ​ VSPAERO will not, for example, model stall characteristics or, in fact, separation of any kind.  This is a tool in your toolbox that will help find much of the aerodynamic traits of a model based on a given set of conditions that are within "​normal"​ flight conditions (e.g. cruise, small alpha, small beta) which you can later modify according to whatever physical limits you feel are necessary. - - This page will describe modeling practices that should increase your chances of success using VSPAERO. ​ By no means is this list comprehensive. ​ The goal is to prevent the usual pitfalls of the learning process while expanding on "good practice"​ methods for analyzing models using numerical codes. ​ An introduction to numerical analysis is given through MIT Open Courseware at this link: [[http://​ocw.mit.edu/​courses/​mathematics/​18-330-introduction-to-numerical-analysis-spring-2012/​ |"​Introduction to Numerical Analysis"​]]. - - ===== Model Detail ===== - - A highly detailed model may look nice, but the chances of needing such fine resolution to solve for aerodynamic characteristics is quite low.  Usually, a much lower resolution will converge to a solution around the expected value  (see figure below). ​ This is true for all numerical methods and holds here as well. - - ^  {{:​vspaero:​vspaeromodeling:​sr22-hd-screen-isoleft.jpg?​direct&​450|High Resolution}} ​ ^  {{:​vspaero:​vspaeromodeling:​sr22-lowres-screen-isoleft.jpg?​direct&​450|Medium Resolution}} ​ ^ - ^  Cirrus SR-22 High Resolution Model  ^  Cirrus SR-22 Medium Resolution Model  ^ - - To compare the two models pictured above, the low resolution model has around 4100 cells and will run to completion in a matter of 5-10 minutes while the high resolution model has 19,200 cells and would take hours. ​ The difference between the results of these two would be less than 5% which is much less than the error typically created in model geometry assumptions. ​ Thankfully, there is a happy medium to be found.  ​ - - Optimizing meshes for numerical solvers is an area of active research and generally follows the following logic: Areas with large gradients get a finer mesh and ignore sections that do not significantly contribute. ​ For example, a fuselage will not significantly contribute to lift or induced drag, so for initial design steps it can generally be left out of most of the analyses. ​ Also, the wing sections can be finely defined to capture effects of downwash or propeller slipstream while leaving most of the wing "​coarsely"​ defined. ​ This is particularly useful when observing low speed conditions where the local Cl is much higher than at cruise. ​ An example of this practice is shown below. - ^  {{ :​vspaero:​vspaeromodeling:​sr22-lift-screen-roughmesh.jpg?​direct&​450 |}}  ^  {{ :​vspaero:​vspaeromodeling:​sr22-lift-screen-bettermesh.jpg?​direct&​450 |}}  ^ - ^  SR-22 Rough Mesh  ^  SR-22 Modified Mesh  ^ - - [[start|Back to Landing Page]] - [[vspaerotutorial|VSPAERO Tutorial]] - - This page was created and edited by:  --- //​[[brandon.l.litherland@nasa.gov|Brandon Litherland]] 2015/07/02 10:47//