{"id":53255,"date":"2021-03-12T14:33:34","date_gmt":"2021-03-12T14:33:34","guid":{"rendered":"\/forum\/forums\/topic\/control-dpm-injection-frequency-in-fluent\/"},"modified":"2021-03-12T14:33:34","modified_gmt":"2021-03-12T14:33:34","slug":"control-dpm-injection-frequency-in-fluent","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/control-dpm-injection-frequency-in-fluent\/","title":{"rendered":"Control DPM injection frequency in Fluent"},"content":{"rendered":"<p>Hi,nI am simulating a particle-air jet and I am interested in the particle-particle collisions. Therefore I am using the DEM collision model available in Fluent. This forces me to work with instationary particles (although I am looking for a steady solution, where the particle collisions dictate the spread). nMy idea is to inject particles, until the fluid and the particles have achieved a steady state. Due to the use of the DEM model, and the collisions between different sized particles, I am using a very small time step (10^-6) while calculating 100 particle iterations during each fluid iteration. Since I am continuously injecting particles, I thought the simulation would be too slow if I had 1 particle time step for each fluid time step, so I increased the number of particle iterations per time step to speed the process up. nThe problem is, even with the stagger Positions option active (I am using the Group injection), particles are injected too frequently, so that overlap and collisions already occur at the injection stage. nIf I change the number of particle iterations to 1 (1:1 particle:fluid iterations) the staggering of particles work. On the other hand, it gets 100 times slower. nMy question is, is there a way to control the particle injection frequency within one fluid time step? Let&#8217;s say, I want to inject every 10 of the 100 particle iterations. Is something like that possible? nOr, would it be possible to make the staggering option work between particle time steps within one fluid time step? (Since I am injecting 100 times per time step only every 100 particle the injection staggering is working).nUsing an UDF I managed to switch injections on and off by changing the injection time (start\/stop) each fluid time step. But then I only inject every 1 of 100 particle iterations (it only lasts one particle iteration each new time step). In this case I would have to change the number of particle iterations to 10 to obtain what I was looking for. But I think, this is just a matter of injecting every nth Particle iteration, there must be an easier way to acess the variable that controls the injections. nThat leads me to the last question. UDF are called at the beginning or end of the fluid iteration. Is there something similar, where I can make changes every particle iteration, without having to set the number of particle iterations to 1? If not, how could I skip the fluid calculation in one fluid time step? Let&#8217;s say I am only interested in dry collisions (DEM Model) in sandblasting. Is that possible in Fluent?.<\/p>\n","protected":false},"template":"","class_list":["post-53255","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["25567"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[" \u0001\u0016?Wz@\u0000UD?7??_?"],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0"],"_btv_view_count":["1195"],"_bbp_subscription":["256836"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["53255"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","182695"],"_bbp_voice_count":["2"],"_bbp_reply_count":["5"],"_bbp_last_reply_id":["147169"],"_bbp_last_active_id":["147169"],"_bbp_last_active_time":["2021-03-19 14:55:57"]},"test":"te_haf"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/53255","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\/53255\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=53255"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}