A gas turbine unit comprising: a compressor and a turbine, extending along a main axis (A; A'; A"); a cooling circuit (12; 112; 212) configured to convey a cooling airflow (AF; AF') from the compressor toward the turbine; and a pre-swirler (15; 115; 215), arranged along the cooling circuit (12; 112; 212) and configured to impart a rotation about the main axis (A; A'; A") to the cooling airflow (AF; AF'); the pre-swirler (15; 115; 215) comprising a plurality of flow channels (17; 117; 217) each having an inlet portion (17a; 117a) with a first passage section (S 1; S 1 '), an outlet portion (17b; 117b) with a second passage section (S 2; S 2 '), and a joining section (17c; 117c) between the inlet portion (17a; 117a) and the outlet portion (17b; 117b); wherein the joining section (17c; 117c) forms a first curve shaped so that a first wall (17d; 118a) of the joining section (17c; 117c), defining an inner side of the first curve, deviates the cooling airflow (AF; AF') about the main axis (A; A'; A") by Coanda effect of an angle correlated to an absolute value of an inlet speed (V I) of the cooling airflow (AF; AF'); and the second passage section (S 2) of the outlet portion (17b; 117b) is such as to allow a plurality of outlet angles of the cooling airflow (AF; AF'), in accordance with the rotation caused by the joining section (17c; 117c); characterized in that the first wall (17d; 118a) of the joining section (17c; 117c) is configured so that the cooling airflow (AF; AF') is deflected about the main axis (A, A'; A") by a greater angle when the inlet speed (V I) is lower in absolute value and by a smaller angle when the inlet speed (V I) is greater in absolute value; wherein the flow channels (17; 117; 217) are shaped so that an outlet speed (V O) of the cooling airflow (AF; AF') at an outlet of the pre-swirler (15; 115; 215) forms an outlet angle ( α) comprised between 40° and 89°, with respect to a direction of the inlet speed (V I); wherein a ratio between the first passage section (S 1; S 1 ') of the inlet portion (17a; 117a) and the second passage section (S 2; S 2 ') of the outlet portion (17b; 117b) is comprised between 0.3 and 3; and wherein a ratio between an equivalent diameter of the first passage section (S 1; S 1 ') of the inlet portion (17a; 117a) and a first curvature radius (R 1; R 1 ') of the first wall (17d; 118a) is comprised between 0.02 and 6. a compressor and a turbine, extending along a main axis (A; A'; A"); a cooling circuit (12; 112; 212) configured to convey a cooling airflow (AF; AF') from the compressor toward the turbine; and a pre-swirler (15; 115; 215), arranged along the cooling circuit (12; 112; 212) and configured to impart a rotation about the main axis (A; A'; A") to the cooling airflow (AF; AF'); the pre-swirler (15; 115; 215) comprising a plurality of flow channels (17; 117; 217) each having an inlet portion (17a; 117a) with a first passage section (S 1; S 1 '), an outlet portion (17b; 117b) with a second passage section (S 2; S 2 '), and a joining section (17c; 117c) between the inlet portion (17a; 117a) and the outlet portion (17b; 117b); wherein the joining section (17c; 117c) forms a first curve shaped so that a first wall (17d; 118a) of the joining section (17c; 117c), defining an inner side of the first curve, deviates the cooling airflow (AF; AF') about the main axis (A; A'; A") by Coanda effect of an angle correlated to an absolute value of an inlet speed (V I) of the cooling airflow (AF; AF'); and the second passage section (S 2) of the outlet portion (17b; 117b) is such as to allow a plurality of outlet angles of the cooling airflow (AF; AF'), in accordance with the rotation caused by the joining section (17c; 117c); characterized in that the first wall (17d; 118a) of the joining section (17c; 117c) is configured so that the cooling airflow (AF; AF') is deflected about the main axis (A, A'; A") by a greater angle when the inlet speed (V I) is lower in absolute value and by a smaller angle when the inlet speed (V I) is greater in absolute value; wherein the flow channels (17; 117; 217) are shaped so that an outlet speed (V O) of the cooling airflow (AF; AF') at an outlet of the pre-swirler (15; 115; 215) forms an outlet angle ( α) comprised between 40° and 89°, with respect to a direction of the inlet speed (V I); wherein a ratio between the first passage section (S 1; S 1 ') of the inlet portion (17a; 117a) and the second passage section (S 2; S 2 ') of the outlet portion (17b; 117b) is comprised between 0.3 and 3; and wherein a ratio between an equivalent diameter of the first passage section (S 1; S 1 ') of the inlet portion (17a; 117a) and a first curvature radius (R 1; R 1 ') of the first wall (17d; 118a) is comprised between 0.02 and 6.