[Samuel Twain]

Dear All:
When I look into the code of constructor of vanDriestDelta class, I am confused what geometricDelta_ is? And I don't know what the function geometricDelta_() means. Could anyone please give me some advice? Each reply would be appreciated.
The code is as follwing:
Foam::LESModels::vanDriestDelta::vanDriestDelta
(
const word& name,
const turbulenceModel& turbulence,
const dictionary& dict
)
:
LESdelta(name, turbulence),
geometricDelta_
(
LESdelta::New
(
IOobject::groupName("geometricDelta", turbulence.U().group()),
turbulence,
// Note: cannot use optionalSubDict - if no *Coeffs dict the
// code will get stuck in a loop attempting to read the delta entry
// - consider looking up "geometricDelta" instead of "delta"?
dict.subDict(type() + "Coeffs")
)
),
kappa_(dict.lookupOrDefault<scalar>("kappa", 0.41)),
Aplus_
(
dict.optionalSubDict(type() + "Coeffs").lookupOrDefault<scalar>
(
"Aplus",
26.0
)
),
Cdelta_
(
dict.optionalSubDict(type() + "Coeffs").lookupOrDefault<scalar>
(
"Cdelta",
0.158
)
),
calcInterval_
(
dict.optionalSubDict(type() + "Coeffs").lookupOrDefault<label>
(
"calcInterval",
1
)
)
{
delta_ = geometricDelta_();
}