{"id":42685,"date":"2020-04-11T08:08:01","date_gmt":"2020-04-11T08:08:01","guid":{"rendered":"\/forum\/forums\/topic\/cl-and-cd-oscillate-in-steady-simulation-for-higher-angles-of-attack\/"},"modified":"2020-04-11T08:08:01","modified_gmt":"2020-04-11T08:08:01","slug":"cl-and-cd-oscillate-in-steady-simulation-for-higher-angles-of-attack","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/cl-and-cd-oscillate-in-steady-simulation-for-higher-angles-of-attack\/","title":{"rendered":"Cl and Cd oscillate in steady simulation for higher angles of attack"},"content":{"rendered":"<p>Hi, I am new to ANSYS FLUENT and I am using it to simulate flow over a s809 airfoil. The simulation is 2D and i created a c-type mesh using ICEM. The Reynolds number of the flow is 2 million and my chord length is 1m. So i calculated the appropriate wall spacing value online with a y+ value of less than 1. I am using the transition SST model as I am trying to validate the results i get with another research paper. So far I have kept all parameters the same to ensure accurate results. I run the steady state simulations while varying the angle of attack (0-15 degrees). The reynolds number is always kept the same and I know for a fact that the airfoil should stall at around 20 degrees. I receive accurate Cl and Cd values up to 10 degrees angle of attack and from 11-15 degrees the values of Cl and Cd start to oscillate. I have attached the images here.&nbsp;<\/p>\n<p><\/p>\n<p>I originally thought it was the mesh so i refined it. But refining the mesh did not change the results I obtained as the mesh is already fine. I dont know why the results oscillate and I think it has something to do with the unsteadiness of the flow. But the airfoil is supposed to stall at 20 degrees so why cant i get converged values of Cl and Cd for angle of attack lower than 20?<\/p>\n<p><\/p>\n<p>Any help would be appreciated!!!<\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/df7fbe66-c457-48e3-a8e9-ab9a005fe2fc\/8e86874a-5c69-435b-8cde-ab9a0085b118_cl.jpg?width=690&amp;upscale=false\" alt=\"Cl graph for AOA - 15&deg;\"><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/df7fbe66-c457-48e3-a8e9-ab9a005fe2fc\/12743fbc-3585-4890-a7c1-ab9a0085cd46_cd.jpg?width=690&amp;upscale=false\" alt=\"Cd graph for AOA - 15&deg;\"><\/p>\n","protected":false},"template":"","class_list":["post-42685","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["14865"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[null],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0"],"_btv_view_count":["623"],"_bbp_subscription":["249742"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["42685"],"_bbp_forum_id":["27792"],"_bbp_engagement":["175580"],"_bbp_voice_count":["1"],"_bbp_reply_count":["0"],"_bbp_last_reply_id":["0"],"_bbp_last_active_id":["42685"],"_bbp_last_active_time":["2020-04-11 08:08:01"]},"test":"sahil1028"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/42685","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/42685\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=42685"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}