ðɪs ɐsˈʌmpʃən mˌeɪks mˈɑːdəlɪŋ ʌv tˈɜːbjʊləns kwˈɔntᵻɾiz ænd sˈɪmplɚ, bˌʌt wɪl nˌɑːt biː ˈækjʊɹət ɪn sənˈæɹiˌoʊz wˌɛɹ ˌænɪsətɹˈɑːpɪk bᵻhˈeɪvjɚɹ ʌv tˈɜːbjʊləns stɹˈɛsᵻz dˈɑːmᵻnˌeɪts, ænd ðɪ ˌɪmplɪkˈeɪʃənz ʌv ðɪs ɪnðə pɹədˈʌkʃən ʌv tˈɜːbjʊləns ˈɔːlsoʊ lˈiːdz tʊ ˌoʊvɚpɹɪdˈɪkʃən sˈɪns ðə pɹədˈʌkʃən dᵻpˈɛndz ɔnðə mˈiːn ɹˈeɪt ʌv stɹˈeɪn, ænd nˌɑːt ðə dˈɪfɹəns bᵻtwˌiːn ðə nˈoːɹməl stɹˈɛsᵻz æz ðeɪ ɑːɹ, baɪ ɐsˈʌmpʃən, ˈiːkwəl.
This assumption makes modelling of turbulence quantities ( and ) simpler, but will not be accurate in scenarios where anisotropic behaviour of turbulence stresses dominates, and the implications of this in the production of turbulence also leads to over-prediction since the production depends on the mean rate of strain, and not the difference between the normal stresses (as they are, by assumption, equal).