{"id":880,"date":"2018-03-21T10:17:52","date_gmt":"2018-03-21T09:17:52","guid":{"rendered":"https:\/\/cfdfeaservice.it\/?p=880"},"modified":"2018-03-20T21:42:23","modified_gmt":"2018-03-20T20:42:23","slug":"come-scegliere-il-modello-di-turbolenza","status":"publish","type":"post","link":"https:\/\/test.cfdfeaservice.it\/index.php\/2018\/03\/21\/come-scegliere-il-modello-di-turbolenza\/","title":{"rendered":"Come scegliere il modello di turbolenza"},"content":{"rendered":"<p>Una delle scelte pi\u00f9 importanti quando si affronta un&#8217;analisi CFD riguarda appunto il modello di turbolenza. I software CFD, ed OpenFOAM in particolare, hanno oramai implementato un grande gamma di modelli che spesso tendono a confondere l&#8217;utente nella scelta. Oggi affronteremo l&#8217;argomento da un punto di vista pratico: vediamo quali sono i parametri che devono influenzare la scelta del modello di turbolenza e come questi devono essere visionati dall&#8217;utente.<\/p>\n<h3>y+ &#8211; Risoluzione a parete<\/h3>\n<p>Tutto parte da un parametro tanto fondamentale quanto difficile da comprendere: la risoluzione a parete (y+). Questo parametro dipende fortemente da tre elementi &#8211; come anche emerge dalla definizione qui riportata:<img data-attachment-id=\"881\" data-permalink=\"https:\/\/test.cfdfeaservice.it\/index.php\/2018\/03\/21\/come-scegliere-il-modello-di-turbolenza\/87247d613a2318517745ad2779940977\/\" data-orig-file=\"https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?fit=84%2C36&amp;ssl=1\" data-orig-size=\"84,36\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"87247d613a2318517745ad2779940977\" data-image-description=\"\" data-medium-file=\"https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?fit=84%2C36&amp;ssl=1\" data-large-file=\"https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?fit=84%2C36&amp;ssl=1\" loading=\"lazy\" src=\"https:\/\/i2.wp.com\/cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?resize=84%2C36&#038;ssl=1\" alt=\"\" width=\"84\" height=\"36\" class=\"aligncenter size-full wp-image-881\" srcset=\"https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?w=84&amp;ssl=1 84w, https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/87247d613a2318517745ad2779940977.png?resize=20%2C9&amp;ssl=1 20w\" sizes=\"(max-width: 84px) 100vw, 84px\" data-recalc-dims=\"1\" \/><\/p>\n<ul>\n<li>Velocit\u00e0 del fluido nella prima cella a parete<\/li>\n<li>Altezza della prima cella a parete<\/li>\n<li>Viscosit\u00e0 del fluido<\/li>\n<\/ul>\n<p>Che importanza ha questo parametro? Fondamentale! Difatti y+ rappresenta la distanza adimensionalizzata da parete ed identifica precisamente il sublayer in cui ogni cella si colloca: sublayer laminare (y+ &lt; 5), sublayer turbolento (30 &lt; y+ &lt; 300) oppure zona di transizione (5 &lt; y+ &lt; 30).<\/p>\n<p><img data-attachment-id=\"882\" data-permalink=\"https:\/\/test.cfdfeaservice.it\/index.php\/2018\/03\/21\/come-scegliere-il-modello-di-turbolenza\/normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates\/\" data-orig-file=\"https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?fit=850%2C822&amp;ssl=1\" data-orig-size=\"850,822\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates\" data-image-description=\"\" data-medium-file=\"https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?fit=300%2C290&amp;ssl=1\" data-large-file=\"https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?fit=750%2C725&amp;ssl=1\" loading=\"lazy\" src=\"https:\/\/i0.wp.com\/cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=484%2C468&#038;ssl=1\" alt=\"\" width=\"484\" height=\"468\" class=\"aligncenter wp-image-882\" srcset=\"https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?w=850&amp;ssl=1 850w, https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=300%2C290&amp;ssl=1 300w, https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=768%2C743&amp;ssl=1 768w, https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=20%2C19&amp;ssl=1 20w, https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=230%2C222&amp;ssl=1 230w, https:\/\/i0.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/Normalized-mean-velocity-profile-in-a-turbulent-boundary-layer-in-semi-log-coordinates.png?resize=600%2C580&amp;ssl=1 600w\" sizes=\"(max-width: 484px) 100vw, 484px\" data-recalc-dims=\"1\" \/><\/p>\n<h4>Modelli di turbolenza e y+<\/h4>\n<p>Ogni modello di turbolenza \u00e8 stato studiato per dare il massimo dell&#8217;accuratezza quando la prima cella a parete rientra all&#8217;interno di un determinato sublayer. Esempi classici, utilizzando i due modelli di turbolenza pi\u00f9 comuni, sono riportati nella seguente tabella.<\/p>\n<table>\n<tbody>\n<tr>\n<td><strong>MODELLO TURBOLENZA<\/strong><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><strong>CONDIZIONE<\/strong><\/td>\n<\/tr>\n<tr>\n<td>k-epsilon<\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\">30 &lt; y+ &lt; 300<\/td>\n<\/tr>\n<tr>\n<td>k-omega SST<\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\"><\/td>\n<td style=\"text-align: center;\">y+ &lt; 5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h4>Condizioni restrittive?<\/h4>\n<p>La domanda che viene fatta molto spesso riguarda la restrittivit\u00e0 di tali condizioni. Rispondere a questa domanda non \u00e8 facilissimo per vari motivi. E&#8217; possibile dire che spesso si utilizzano wall-functions, ovvero funzioni di parete, che permettono di non rispettare alla perfezione le direttive espresse in precedenza.<\/p>\n<h4>Come applicare la teoria?<\/h4>\n<p>L&#8217;applicazione di quanto visto in questo post \u00e8 estremamente semplice. Si svolge un&#8217;analisi CFD di prova da cui estrarre i valori di y+ a parete (OpenFOAM produce tale parametro in maniera automatica). Stimato tale valore di y+ \u00e8 possibile riavviare la simulazione scegliendo il modello di turbolenza appropriato.<\/p>\n<p><strong>_________________________________<\/strong><\/p>\n<p><strong>CFD FEA Service SRL<\/strong> &egrave; una societ&agrave; di servizi che offre <em>consulenza<\/em> e <em>formazione<\/em> in ambito <strong>ingegneria<\/strong> e <strong>IT<\/strong>. Se questo post\/prodotto ti &egrave; piaciuto ti invitiamo a:<\/p>\n<ul>\n<li>visionare il nostro <a href=\"https:\/\/cfdfeaservice.it\/index.php\/blog\/\" target=\"_blank\" rel=\"noopener\">blog<\/a><\/li>\n<li>visionare i <a href=\"https:\/\/cfdfeaservice.it\/index.php\/prodotti\/\" target=\"_blank\" rel=\"noopener\">software<\/a> disponibili - anche per la formazione<\/li>\n<li>iscriverti alla nostra newsletter<\/li>\n<li>entrare in contatto con noi attraverso la <a href=\"https:\/\/cfdfeaservice.it\/#ribbon\" target=\"_blank\" rel=\"noopener\">pagina contatti<\/a><\/li>\n<\/ul>\n<p>Saremo lieti di seguire le tue richieste e fornire risposte alle tue domande.<\/p>","protected":false},"excerpt":{"rendered":"<p>Una delle scelte pi\u00f9 importanti quando si affronta un&#8217;analisi CFD riguarda appunto il modello di turbolenza. I software CFD, ed OpenFOAM in particolare, hanno oramai implementato un grande gamma di modelli che spesso tendono a confondere l&#8217;utente nella scelta. Oggi affronteremo l&#8217;argomento da un punto di vista pratico: vediamo quali [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":883,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[26,33],"tags":[],"jetpack_featured_media_url":"https:\/\/i1.wp.com\/test.cfdfeaservice.it\/wp-content\/uploads\/2018\/03\/turbulence.jpeg?fit=259%2C194&ssl=1","yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v15.1.1 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Come scegliere il modello di turbolenza - CFD FEA\/FEM Service<\/title>\n<meta name=\"description\" content=\"Visione d&#039;insieme dei modelli di turbolenza disponibili e di come effettuare la scelta migliore per garantire risultati accurati alle vostre simulazioni.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/test.cfdfeaservice.it\/index.php\/2018\/03\/21\/come-scegliere-il-modello-di-turbolenza\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Come scegliere il modello di turbolenza - 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