GASP BWB Aero Implementation

[xjjiang]

Summary

This PR implements GASP aerodynamics subsystems for BWB aircraft. Five new components are added:

• BWBBodyLiftCurveSlope
• BWBFormFactorAndSIWB
• BWBAeroSetup
• BWBLiftCoeff
• BWBLiftCoeffClean

Two group components CruiseAero and LowSpeedAero are configured for BWB as an option (default to conventional aircraft).

Currently, there are only three unit tests: one for cruise and two for low speed aero. Now, nineteen new unit tests are added for individual components using BWB data.

In GASP, friction due to nacelle is removed from the computation of SA5 (see below). Instead, it is computed separately and is added in the drag computation.

alpha_stall and CL_max are computed based on wing only. We expect that they will be updated in the future.

Table based aerodynamics is still available to BWB. A new table based BWB model will be provided in the future.

Comparison of BWBAeroSetup with GASP

Variables	GASP	Variables	Aviary
CLAW	4.63868	lift_curve_slope	4.63868
BARL	-0.14081	lift_ratio	-0.14081
CFIN	0.002836	cf	0.002836
SA1	0.81401	SA1	0.80832
SA2	-0.15743	SA2	-0.13651
SA3	0.033989	SA3	0.033989
SA4	0.10197	SA4	0.10197
SA5	0.004464	SA5	0.009628
SA6	2.23877	SA6	2.09277
SA7	0.034136	SA7	0.040498

The differences are due to several reasons:

• GASP has different coefficients of friction for different part of an aircraft. For this purpose, several new parameters (aero calibration factors) are added. Aviary has one single coefficient cf.
• GASP has several factors that are included in the computation of friction (e.g. winglet, tip tank, excrescence) but not in Aviary.
• GASP excludes frictions from nacelle in SA5. Nacelle friction is done in engine computation and is added in drag computation. But in Aviary, nacelle friction is included in SA5 and not in drag computation.

Comparison of CruiseAero with GASP

Variables	GASP	Variables	Aviary
CL	0.41069	CLTOT	0.41067
CD	0.014738	CD	0.022509
CL/CD	27.86518	L/D	18.24451

As we see, CL matches closely but CD doesn't. This is because the differences in BWBAeroSetup (see above).

Comparison of LowSpeedAero with GASP

Variables (Takeoff)	CL (GASP/Aviary)	CD (GASP/Aviary)	CL/CD (GASP/Aviary)
α = -2.0	0.07507 / 0.05787	0.01853 / 0.02565	4.05136 / 3.307513
α = 0.0	0.23964 / 0.21906	0.01866 / 0.02592	12.84433 / 9,49165
α = 2.0	0.40422 / 0.407231	0.02070 / 0.02844	20.74018 / 16.22583

Variables (Landing)	CL (GASP/Aviary)	CD (GASP/Aviary)	CL/CD (GASP/Aviary)
α = -2.0	0.18551 / 0.19824	0.02299 / 0.02962	8.06918 / 6.69194
α = 0.0	0.35009 / 0.35944	0.02292 / 0.02970	15.27225 / 12.10145
α = 2.0	0.51467 / 0.52062	0.02482 / 0.03209	20.74018 / 16.22583

As we see, CL matches closely but CD doesn't. This is because the differences in BWBAeroSetup (see above).

Related Issues

• Resolves #

Backwards incompatibilities

None

New Dependencies

None