Matthew W. Tufts

Effects of Step Excrescences on Swept-Wing Transition

An in-flight test article mounted on a Cessna O-2A Skymaster studying the effect of forwardand aft-facing steps on swept-wing boundary-layer transition is described. An accurate instrumentation suite, consisting of a five-hole probe, static pressure ports, and an infrared camera is presented. Pressure coefficient profiles compare favorably with a computational validation. Infrared thermography is used as a global transition detection technique. Step height and transition location based Reynolds numbers are computed and compared with unswept transition studies. Based on the current data, the addition of the crossflow instability is believed to reduce the critical step height Reynolds number for both forwardand aft-facing steps.

Effects of Step Excrescences on a Swept Wing in a Low-Disturbance Wind Tunnel

A 30° swept-wing model with a movable, leading-edge extending to 15% chord is used in low-disturbance wind-tunnel tests to study the effect of two-dimensional, step excrescences in a three-dimensional boundary layer. Forwardand aft-facing steps are modulated during the tests. Pressure measurements are compared with computational results, infrared thermography is used to globally detect boundary-layer transition, and hotwire measurements provide details of the boundary-layer profiles in the vicinity of the steps. An analysis of the results is provided including data from tests in a flight environment and from experimental studies of an unswept model of equivalent 2-D pressure gradient.

A Transonic Laminar-Flow Wing Glove Flight Experiment: Overview and Design Optimization

The Subsonic Aircraft Roughness Glove Experiment (SARGE) is a hybrid natural laminar flow and passive laminar flow control flight test that will be carried out under the auspices of the NASA Environmentally Responsible Aviation initiative. The primary goals of the SARGE experiment are to 1) achieve natural laminar flow to 0.60 chord on the suction side at up to 22 million chord Reynolds number and 2) at conditions of at least 22 million chord Reynolds number, demonstrate the effectiveness of a passive array of discrete roughness elements in extending laminar flow beyond the natural transition location. The test will be conducted on a test article having 35° leading-edge sweep at 0.75 Mach and lift coefficient of at least 0.5. In cooperation with NASA Dryden Flight Research Center, Texas A&M has completed the optimized aerodynamic design of the wing glove, as well as flight test and instrumentation planning.

Design of the Subsonic Aircraft Roughness Glove Experiment (SARGE)

The Subsonic Aircraft Roughness Glove Experiment (SARGE) is a hybrid natural laminar flow and passive laminar flow control flight test that will be carried out under the auspices of the NASA Environmentally Responsible Aviation initiative. Texas A&M has completed the initial aerodynamic design of a wing glove to be installed on a NASA Gulfstream III testbed. The primary goals of the SARGE experiment are to 1) achieve natural laminar flow to 0.60 chord on the suction side at up to 22 million chord Reynolds number and 2) at conditions of at least 22 million chord Reynolds number, demonstrate the effectiveness of passive Discrete Roughness Elements in extending laminar flow beyond the natural transition location. Computations of the flight test configuration flowfield and the initial design of a laminar flow wing glove are presented, followed by a description of the proposed flight test experiment as well as the instrumentation suite. The initial design is shown to marginally fulfill the design requirements. Efforts are underway to optimize the design to improve spanwise flow uniformity and provide better stabilization of streamwise instabilities.

Effects of Step-Excrescence Location on Swept-Wing Transition

Two-dimensional step excrescences on a swept-wing model are studied in two lowdisturbance environments, wind-tunnel and flight. The present study focuses at 1% chord. An extensive comparison is made with previous flight and wind-tunnel results at 15% chord using the same test article and same initial and boundary conditions. The combined sensitivity of curvature effects and streamwise location of the step excrescence is examined. Infrared thermography and hotwire anemometry results are presented and will be used to validate the companion computational effort by Tufts et al.

Flight experiments on the effects of step excrescences on swept-wing transition

A 30° swept-wing model with a movable, leading-edge extending to 15% chord is used in flight tests to study the effect of two-dimensional, step excrescences on swept-wing transition, where stationary-crossflow waves are typically the dominant instability. Transport unit Reynolds numbers are achieved using a Cessna O-2A Skymaster. Forward- and aft-facing steps are modulated in-flight. Pressure measurements are compared with CFD. Infrared thermography is used to globally detect boundary-layer transition. When the 2-D pressure gradient matches the unswept case, the swept-wing case has a lower Rekk,crit. However, there is still potential to relax conventional, laminar-flow tolerances for steps.

Computational design of a test article to investigate 2-D surface excrescences on a swept laminar-flow wing

The construction of a spanwise-invariant swept-wing test article designed to facilitate the inclusion of a range of two-dimensional (2-D) step and gap excrescences in flight via an internal articulation mechanism has been completed. Using a finite-element Navier-Stokes solution and a spectrally accurate boundary-layer solver, coupled with stability analyses, the model has been designed to be subcritical to all instabilities except the crossflow instability. The model can be safely flown in a flight experiment, and be mounted in the Klebanoff-Saric Wind Tunnel at Texas A&M University. The model can be tested at multiple angles of attack (pressure gradients), as well as multiple Reynolds numbers, including unit Reynolds numbers typical of transports. Stability behaviour of the test article was designed to be conducive to a thorough examination of the interaction between an inherent crossflow instability and the shear layer created by the step and gap excrescences. The computations and experiments will together provide data and correlations complementing the previous studies of 2-D excrescences on an unswept flat plate and wedges subject to favourable pressure gradients by The Northrop Grumman Corporation. The current paper focuses on the design and stability analyses of the smooth-wing test article, that is, without excrescences present, as a baseline configuration.

Design of an Infinite-Swept-Wing Glove for In-Flight Discrete-Roughness-Element Experiment

The Subsonic Aircraft Roughness Glove Experiment is an in-flight experiment designed to meet the NASA Environmentally Responsible Aviation project requirements. The goal of the experiment was to demonstrate the discrete-roughness-element technology to delay transition on a swept wing at transport-relevant conditions and subject to crossflow instability. In this paper, a redesign of that experiment is described for a different aircraft (Gulfstream-IIB), meeting the same requirements, but using a new methodology that promotes infinite-swept-wing flow on the glove test article. The new glove has the designation TAMU-0706. Increasing the demonstrated capabilities of both natural laminar flow and discrete roughness elements is a large step toward practical laminar flow on transport aircraft. Moreover, the infinite-swept-wing flow methodology not only increases the effective test region of the wing glove, but is well adapted for code-validation studies of discrete roughness element and other laminar-flow-contro...

Computational Investigation of the Effects of Surface Imperfections and Excrescences on the Crossflow Instability

This paper describes a computational investigation and companion to the current work at the Texas A&M Engineering Experiment Station (TEES) Flight Research Lab (FRL). The FRL is both operating an O-2A aircraft and conducting wind tunnel tests in the Klebanoff Saric Wind Tunnel (KSWT) in the investigation of surface excrescences on the transition of laminar to turbulent flow. Using a finite-element Navier-Stokes solution and a spectrally accurate boundary-layer solver, coupled with linear and nonlinear stability analyses, it is proposed to quantify the effect of surface imperfections and outer mold line (OML) non-uniformities on crossflow instabilities. The quantitative goal of the proposed research is to computationally evaluate a wide parameter space of step heights and gaps, and develop correlation models between geometry and estimated effect on transition for use by designers. The proposed computations will be validated against experiments on the physical model both in-flight and in the KSWT, and vice versa, in a tightly integrated program. This paper is a companion paper to “Effects of Step Excrescences on Swept-Wing Transition” by Duncan et al. also submitted to the 31st Applied Aerodynamics Conference.

Design of an Infinite Swept Wing Glove for an In-Flight DRE Experiment

The Subsonic Aircraft Roughness Glove Experiment (SARGE) is an in-flight experiment designed to meet NASA Environmentally Responsible Aviation (ERA) project requirements. The goal of the experiment was to demonstrate the discrete-roughness-element (DRE) technology to delay transition on a swept wing at transport-relevant conditions and subject to crossflow instability. In this paper a redesign of that experiment is described for a different aircraft (G-IIB), meeting the same requirements but using a new methodology that promotes infinite-swept-wing flow on the glove test article. The new glove has the designation TAMU-0706. Increasing the demonstrated capabilities of both natural laminar flow (NLF) and DREs is a large step towards practical laminar flow on transport aircraft. Moreover, the infinite-swept-wing flow methodology not only increases the effective test region of the wing glove but is well adapted for code-validation studies of DRE and other laminar-flow-control (LFC) technologies.