Engineering Papers⌕ Search

Engineering topics

Chen, Fang-Jenq

Publications and source records attributed to Chen, Fang-Jenq.

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Boundary Layer Transition Experiments in Support of the Hypersonics Program

Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.

Berry, Scott A.↗
NASA NTRS2002

Virtual Shaping of a Two-dimensional NACA 0015 Airfoil Using Synthetic Jet Actuator

The Aircraft Morphing Program at NASA Langley envisions an aircraft without conventional control surfaces. Instead of moving control surfaces, the vehicle control systems may be implemented with a combination of propulsive forces, micro surface effectors, and fluidic devices dynamically operated by an intelligent flight control system to provide aircraft maneuverability over each mission segment. As a part of this program, a two-dimensional NACA 0015 airfoil model was designed to test mild maneuvering capability of synthetic jets in a subsonic wind tunnel. The objective of the experiments is to assess the applicability of using unsteady suction and blowing to alter the aerodynamic shape of an airfoil with a purpose to enhance lift and/or to reduce drag. Synthetic jet actuation at different chordwise locations, different forcing frequencies and amplitudes, under different freestream velocities are investigated. The effect of virtual shape change is indicated by a localized increase of surface pressure in the neighborhood of synthetic jet actuation. That causes a negative lift to the airfoil with an upper surface actuation. When actuation is applied near the airfoil leading edge, it appears that the stagnation line is shifted inducing an effect similar to that caused by a small angle of attack to produce an overall lift change.

Chen, Fang-Jenq↗
NASA NTRS1999

Transitioning Active Flow Control to Applications

Active Flow Control Programs at NASA, the U.S. Air Force, and DARPA have been initiated with the goals of obtaining revolutionary advances in aerodynamic performance and maneuvering compared to conventional approaches. These programs envision the use of actuators, sensors, and controllers on applications such as aircraft wings/tails, engine nacelles, internal ducts, nozzles, projectiles, weapons bays, and hydrodynamic vehicles. Anticipated benefits of flow control include reduced weight, part count, and operating cost and reduced fuel burn (and emissions), noise and enhanced safety if the sensors serve a dual role of flow control and health monitoring. To get from the bench-top or laboratory test to adaptive distributed control systems on realistic applications, reliable validated design tools are needed in addition to sub- and large-scale wind-tunnel and flight experiments. This paper will focus on the development of tools for active flow control applications.

Joslin, Ronald D.↗
NASA NTRS1997

Application of Least-Squares Adjustment Technique to Geometric Camera Calibration and Photogrammetric Flow Visualization

Flow visualization produces data in the form of two-dimensional images. If the optical components of a camera system are perfect, the transformation equations between the two-dimensional image and the three-dimensional object space are linear and easy to solve. However, real camera lenses introduce nonlinear distortions that affect the accuracy of transformation unless proper corrections are applied. An iterative least-squares adjustment algorithm is developed to solve the nonlinear transformation equations incorporated with distortion corrections. Experimental applications demonstrate that a relative precision on the order of 40,000 is achievable without tedious laboratory calibrations of the camera.

Chen, Fang-Jenq↗
NASA NTRS1993

Boundary-layer transition extent measurements on a cone and flat plate at Mach 3.5

Wide excursions of the boundary-layer transition region are expected to occur on the X-30 National Aerospace Plane (NASP) due to the high Mach number, high temperature, and low density environment experienced during flight. Undesirable features of the transition region, such as the peak heat transfer rate, make it important to understand transition region physics. The current study investigates transition extent in 2D and axisymmetric bounday-layer flows. Surface-pitot and recovery temperature data obtained on a cone and flat plate at Mach 3.5 in the Supersonic Low-Disturbance Pilot Tunnel at NASA Langley are presented. Results show the effects of the unit Reynolds number, freestream disturbances, and nose/leading-edge bluntness on the extent of transition.

Chen, Fang-Jenq↗
NASA NTRS1991

Goertler instability and hypersonic quiet nozzle design

A concept for nozzle design which incorporates slow expansion rates and a radial flow region is developed for use on a hypersonic (Mach 6) nozzle. It is shown that the boundary-layer suction slot upstream of the nozzle throat is necessary to remove upstream turbulent boundary layers and to initialize a new laminar boundary layer on the downstream nozzle wall. In effect, the laminar boundary-layer flow can be extended more effectively farther downstream by a slow expansion contour based on the present design concept than by a rapid expansion contour used in previous pilot quiet nozzles.

Chen, Fang-Jenq↗
NASA NTRS1990

Advanced Mach 3.5 Axisymmetric Quiet Nozzle

To advance boundary-layer stability and transition research and to ultimately provide reliable predictions of transition for supersonic flight vehicles, a wind tunnel is required with very low stream disturbance levels comparable to free flight conditions. Experimental and theoretical research to develop a low-disturbance supersonic wind tunnel has achieved a breakthrough. A new concept for nozzle design is presented which promises a large increase in the length of the quiet test core. The Advanced Mach 3.5 Axisymmetric Quiet Nozzle is the first prototype built to prove the new design concept. Experimental results from this new nozzle on the extent of laminar wall boundary layers are compared with data from other nozzles and with theoretical predictions based on linear stability theory. The Reynolds numbers based on the measured length of the quiet test core for this new nozzle are in excellent agreement with the theoretical predictions. The effect of surface finish on the nozzle performance is also discussed.

Chen, Fang-Jenq↗
NASA NTRS1990

On the design of a new Mach 3.5 quiet nozzle

To advance boundary-layer stability and transition research and to ultimately provide reliable predictions of transition for supersonic flight vehicles, a wind tunnel is required with very low stream disturbance levels comparable to free flight conditions. A new concept for nozzle design is presented which promises a large increase in the length of the quiet test core. The Advanced Mach 3.5 Axisymmetric Quiet Nozzle is the first prototype built to prove the new design concept. The Reynolds numbers based on the measured length of the quiet test core for this new nozzle are in excellent agreement with the theoretical predictions.

Chen, Fang-Jenq↗