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Prandtl 's mixing-length concept Later , Ludwig Prandtl introduced the additional concept of the mixing length , along with the idea of a boundary layer .
 Prandtl, Ludwig Prandtl
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Prandtl, Ludwig Prandtl