> Пробовал задать диапазон, но это не помогло, график тот же.

gnuplot> plot "turb.txt" using 1:2 with lines lt rgb "black" lw 2 title "first",\    
>"turb.txt" using 1:3 with lines lt rgb "grey" lw 2 title "second"\
>"turb.txt" using 1:4 with lines lt "blue" lw 2 title "third"

         warning: Skipping data file with no valid points

gnuplot> plot "turb.txt" using 1:2 with lines lt rgb "black" lw 2 title "first","turb.txt" using 1:3 with lines lt rgb "grey" lw 2 title "second""turb.txt" using 1:4 with lines lt "blue" lw 2 title "third"
                                                                                                                                                 ^
         unexpected or unrecognized token

gnuplot> set xrange [0:1000]
gnuplot> set yrange [0:1.5]

и нивкакую.

синтаксис брал отсюда:
https://www.youtube.com/watch?v=ZEUHCx8gKvI