Experimental and Computational Sonic Boom Assessment of Boeing N+2 Low Boom Models

Abstract

Near-field pressure signatures were measured and computational predictions made for several sonic boom models representing Boeing's Quiet Experimental Validation Concept (QEVC) supersonic transport, as well as for three axisymmetric calibration models. The concept was designed under a NASA Research Announcement (NRA) contract to address environmental and performance goals, specifically for low sonic boom loudness levels and high cruise efficiency, for an aircraft anticipated to enter service in the 2020-timeframe. Wind tunnel tests were conducted on the aircraft and calibration models during Phases I and II of the NRA contract from 2011 to 2013 in the NASA Ames 9-by 7-Foot and NASA Glenn 8-by 6-Foot Supersonic Wind Tunnels. Sonic boom pressure signatures were acquired primarily at Mach 1.6 and 1.8, and force and moment data were acquired from Mach 0.8 to 1.8. The sonic boom test data were obtained using a 2-in. flat-top pressure rail and a 14-in. tapered "reflection factor 1" (RF1) pressure rail. Both rails capture an entire pressure signature in one data point, and successive signatures at varying positions along or above the rail were used to improve data quality through spatial averaging. The sonic boom data obtained by the rails were validated with high-fidelity numerical simulations of offbody pressures. The test results showed good agreement between the computational and experimental data when a variety of testing techniques including spatial averaging of a series of pressure signatures were employed. The two wind tunnels generally produced comparable data. NomenclatureCAD = computer-aided design CoR = center of rotation h, h_nose = model altitude at model nose, in. h/L, h_nose_L = model altitude non-dimensionalized by model length HumidAvg = average humidity from wind tunnel sensors, ppm by weight L = model reference length, in. M = Mach number

Computational and Experimental Study of Plume and Shock Interaction Effects on Sonic Boom in the NASA Ames 9x7 Supersonic Wind Tunnel

“…In this paper, the pressure signature represents the signature of overpressure coefficient, which is a dimensionless parameter that describes the relative pressures throughout the flow field and is defined as ∆P/P∞ = (P -P∞) / P∞. Error bars on the experimental data show +/-2 sigma [16]. The nozzle was run alone as a starting point to obtain the sonic boom signature of the model itself.…”

“…Wind tunnel data was obtained at Mach 1. at increments along the pressure rail, to take averaged data points for 10 seconds. Spatial averaging was used on the data points taken in the x-direction along the rail to produce a signature with reduced effects from the tunnel flow field spatial distortions [16]. Reference runs were taken with the model out of "view" of the pressure rail, and then subtracted from the data runs, to remove tunnel effects from the signatures (Equation 2).…”

“…Reference runs were taken with the model out of "view" of the pressure rail, and then subtracted from the data runs, to remove tunnel effects from the signatures (Equation 2). The two-sigma uncertainty of the experimental data was calculated using the method described in reference 16.…”

The Need for Advanced Simulations for Advanced Air Vehicle Concepts

“…NASA recently developed an approach that couples these two design aspects, employing an adjoint-based inverse method to create a conceptual design tool [24][25][26] . This development effort has been very comprehensive and involves more than just being able to develop an OML based on a single point on the ground.…”