diff --git a/code/code_gen/code_gen.py b/code/code_gen/code_gen.py
index 5042eaa..2f14efa 100644
--- a/code/code_gen/code_gen.py
+++ b/code/code_gen/code_gen.py
@@ -32,6 +32,7 @@ calc_grammar = """
     ?atom: NUMBER           -> number
          | "-" atom         -> neg
          | NAME             -> var
+         | NAME "'"         -> fluc
          | "$" NAME         -> env
          | "(" sum ")"
          | inlinefunc "(" sum ")" -> icall
@@ -144,6 +145,13 @@ class CalculateTree(Transformer):
             dep.append(name.value)
         return (name + "(i,j,k)", dep)
 
+    def fluc(self, name):
+        dep = []
+        if name not in self.primary:
+            dep.append(name.value)
+        fmt = "({0}(i,j,k) - avg_{0}(i))"
+        return (fmt.format(name) , dep)
+
     def env(self, name):
         return (name, [])
 
diff --git a/code/code_gen/terms.input b/code/code_gen/terms.input
index 5c7062b..94d44bf 100644
--- a/code/code_gen/terms.input
+++ b/code/code_gen/terms.input
@@ -4,7 +4,14 @@ c_auto = 1.0 - y
 wrate_auto = rxn_rate(c_auto)
 fsd_auto = sqrt (sqr(ddx(c_auto)) + sqr(ddy(c_auto)) + sqr(ddz(c_auto)))
 
-avg { u, v, w}
-avg c_auto { u, v, w}
-avg y { u, v, w}
+k = (sqr(u')+sqr(v')+sqr(w'))/2.0
+
+tflux = u' * c_auto'
+
+avg { u, v, w, c_auto }
+
+avg c_auto { u, v, w }
+
+avg y { u, v, w }
+
 avg fsd_auto { u }