Inverse Design of Low-Boom Supersonic Concepts Using Reversed Equivalent-Area Targets

Abstract

A promising path for developing a low-boom configuration is a multifidelity approach that (1) starts from a low-fidelity low-boom design, (2) refines the low-fidelity design with computational fluid dynamics (CFD) equivalent-area (A e ) analysis, and (3) improves the design with sonic-boom analysis by using CFD off-body pressure distributions. The focus of this paper is on the third step of this approach, in which the design is improved with sonicboom analysis through the use of CFD calculations. A new inverse design process for offbody pressure tailoring is formulated and demonstrated with a low-boom supersonic configuration that was developed by using the mixed-fidelity design method with CFD A e analysis. The new inverse design process uses the reverse propagation of the pressure distribution (dp/p) from a mid-field location to a near-field location, converts the near-field dp/p into an equivalent-area distribution, generates a low-boom target for the reversed equivalent area (A e,r ) of the configuration, and modifies the configuration to minimize the differences between the configuration's A e,r and the low-boom target. The new inverse design process is used to modify a supersonic demonstrator concept for a cruise Mach number of 1.6 and a cruise weight of 30,000 lb. The modified configuration has a fully shaped ground signature that has a perceived loudness (PLdB) value of 78.5, while the original configuration has a partially shaped aft signature with a PLdB of 82.3. Nomenclature

Conceptual Design of Low-Boom Aircraft with Flight Trim Requirement

“…The offbody pressure distribution is propagated backward in time with sBOOM to a location near the aircraft, and it is converted into an equivalent area A rev e . It is important to note that there is a small error associated with the backward propagation of the offbody pressure distribution [7]. This error is introduced by approximations due to regularization in sBOOM and is considered acceptable for low-boom design.…”

“…This paper presents a new approach for generating low-boom targets that are capable of driving the design toward a trimmed state. The formulation uses a surrogate lift distribution to predict the location of cp x corresponding to a presumed aircraft geometry with a reversed equivalent area A rev e [7] that matches the target A e . It is also important to note that, although closely related to trim, longitudinal stability is not addressed by this design approach.…”

Advanced Usage of Vehicle Sketch Pad for CFD-Based Conceptual Design

“…Once the difference between the target equivalent area and the reversed equivalent area is relatively small in comparison to the fuselage equivalent area, one can scale the area distribution of the fuselage/pod cross sections to eliminate the difference and obtain a low-boom configuration [10]. The difficulty for the fuselage volume shaping is the determination of a parameterization scheme for the fuselage area distribution that will yield the required distribution for a low-boom configuration.…”

“…The cruise weight for the optimized configuration decreased to 27,000 lbs as a result of the modifications to the horizontal tail. See [10] for more details. …”

“…A case study for volume shaping with BOSS was demonstrated by Li and Rallabhandi [10] to shape the ground signature propagated from an off-body pressure distribution. The design process consists of fuselage and pod shaping for matching reversed equivalent area (A e,r ) to a low-boom target, followed by a design of experiments (DOE) for modification of the aft shape of the reversed equivalent area.…”