螺旋 is a more technical term for a helix or spiral, often used in scientific contexts, whereas 渦巻き形 is more descriptive and everyday.
Standard spelling with okurigana.
Variant without okurigana; less common but still used.
Compound of 渦巻き (uzumaki, 'whirlpool, spiral') + 形 (kata, 'shape, form').