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Gartenberg, Ehud

Publications and source records attributed to Gartenberg, Ehud.

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

A concept for transition mapping on a 10 deg-cone in the National Transonic Facility using flow-pressure variation

A conceptual study was performed to define a technique for mapping the boundary-layer transition on a 10 deg-Cone in the National Transonic Facility (NTF) as a means of determining this cryogenic-tunnel suitability for laminar flow testing. A major challenge was to devise a test matrix using a fixed surface pitot probe, varying the flow pressure to pr oduce the actual Reynolds numbers for boundary-layer transition. This constraint resulted from a lack of a suitable and reliable electrical motor to drive the probe along the cone's surface under cryogenic flow conditions. The initial phase of this research was performed by the author in collaboration with the late Dr. William B. Igoe from the Aerodynamics Division at NASA Langley Research Center. His comments made during the drafting of this document were invaluable and a source of inspiration.

Gartenberg, Ehud↗
NASA NTRS1994

Boundary-layer transition detection with infrared imaging emphasizing cryogenic applications

This paper reviews the technique of boundary-layer transition detection using infrared (IR) imaging, emphasizing cryogenic wind-tunnel testing. With the exception of the low-temperature effects on the IR radiation, the discussion is relevant to conventional wind-tunnel and flight testing as well. At low temperatures, IR imaging encounters a reduction in the radiated energy throughout the IR spectrum, combined with a shift to longer wavelengths of the bulk of the radiation. This radiation behavior affects the minimum resolvable temperature difference (MRTD) of the IR imaging system because of its fixed wave band sensitivity. In the absence of commercial long wavelength IR imaging systems, operating at wavelengths longer than 13 micron, some measures can be taken to alleviate the problem caused by the MRTD limitation. The thermal signature of transition can be enhanced by allowing a small and controlled temperature increase of the wind-tunnel flow that induces a transient heat transfer to the model. This action temporarily reveals the model area under the turbulent regime through its higher heating rate compared with the laminar regime. The contrast between the areas exposed to the two regimes can be enhanced by subtraction of thermograms (the equilibrium thermogram from the transient thermogram). Further visual improvement can be obtained through shade stretching or binary shading.

Gartenberg, Ehud↗
NASA NTRS1994

Aerodynamic Investigation with focusing schlieren in a cryogenic wind tunnel

A flow visualization study was performed using a focusing schlieren system in the 0.3m Transonic Cryogenic Tunnel at NASA Langley Research Center. The system proved to be a useful flow visualization tool for flows as low as M = 0.4. This study marked the first verification of the focusing schlieren technique in a major subsonic/transonic wind tunnel and the first time that high-quality, detailed pictures of high-Reynolds-numbers flows were obtained in a cryogenic wind tunnel. This test was part of a development program to implement instrumentation techniques in cryogenic wind tunnels, with the ultimate aim to use them in the National Transonic Facility (NTF).

Gartenberg, Ehud↗
NASA NTRS1993

Aerodynamic investigation with focusing schlieren in a cryogenic wind tunnel

A flow visualization study was performed using a focusing schlieren system in the 0.3m Transonic Cryogenic Tunnel at NASA Langley Research Center. The design employed proved to be a useful flow visualization tool for flows as low as M = 0.4. This study marked the first verification of the focusing schlieren technique in a major subsonic/transonic wind tunnel, and the first time that high quality, detailed pictures of high-Reynolds number flows were obtained in a cryogenic wind tunnel. This test was part of a development program to implement instrumentation techniques in cryogenic wind tunnels, with the ultimate aim to use them in the National Transonic Facility (NTF).

Gartenberg, Ehud↗
NASA NTRS1992

Twenty-five years of aerodynamic research with infrared imaging

A review is presented of the commercial introduction of IR imaging systems in the midsixties that has opened the possibilities to visualize viscous interactions between a body and the surrounding airflow by mapping the surface temperature distributions on configurations of interest. The capability of IR imaging systems to produce in real-time thermograms, which can be interpreted both locally and globally, makes them useful for heat transfer and skin-friction aerodynamic studies. Attention is given to IR systems and data processing, supersonic and hypersonic studies, Space Shuttle flight experiments, subsonic and transonic studies, and propulsion studies.

Gartenberg, Ehud↗
NASA NTRS1992

Milestones in boundary-layer transition research with infrared imaging

Since its first use in aerodynamic testing in 1967, IR imaging techniques have made distinctive contributions to two major development programs: the configurational design of the Space Shuttle, and the laminar-flow wing program of the Advanced Technologies Testing Aircraft System (ATTAS). In the case of the Space Shuttle, IR imaging was uniquely able to generate transition and heat-transfer data while retaining full control of thermal protection tile-system surface roughness. In ATTAS, much boundary layer transition data was produced with otherwise unobtainable time- and cost-efficiency.

Gartenberg, Ehud↗
NASA NTRS1991

Airfoil transition and separation studies using an infrared imaging system

An infrared imaging system was used to detect the thermal signature of boundary-layer flow regimes on a NACA 0012 airfoil from zero angle of attack up to separation. The boundary-layer transition from laminar to turbulent flow and the onset of separation could be seen on the airfoil thermograms. The findings were compared against the behavior of aluminum foil tufts observable both visually and with the infrared imaging system. This arrangement offers the option of using the infrared imaging system both for flow regime detection through surface thermography and flow visualization by the aluminum foil tufts. Ultimately the surface temperature changes due to variation in the angle of attack of a lifting surface provide a means for interpretation of the boundary-layer flow regimes.

Gartenberg, Ehud↗
NASA NTRS1991

Mapping flowfields with a heated wire and an infrared imaging system

IR imaging system measurements of longitudinal temperature variations created in wakes, jet flows, etc. by an electrically heated wire can furnish indications of air velocity distributions through Nusselt number correlations. These correlations can either account for, or minimize and neglect, wire conduction and radiation effects under steady state conditions. The IR imaging system whose experimental use is presently evaluated employs an InSb detector sensitive to 3.5-5.6-micron IR emissions.

Gartenberg, Ehud↗
NASA NTRS1991

Convective response of a wall-mounted hot-film sensor in a shock tube

Shock tube experiments were performed in order to determine the response of a single hot-film element of a sensor array to transiently induced flow behind weak normal shock waves. The experiments attempt to isolate the response due only to the change in convective heat transfer at the hot-film surface mounted on the wall of the shock tube. The experiments are described, the results being correlated with transient boundary layer theory and compared with an independent set of experimental results. One of the findings indicates that the change in the air properties (temperature and pressure) precedes the air mass transport, causing an ambiguity in the sensor response to the development of the velocity boundary layer. Also, a transient, local heat transfer coefficient is formulated to be used as a forcing function in an hot-film instrument model and simulation which remains under investigation.

Roberts, A. Sidney, Jr.↗
NASA NTRS1991

Twenty-five years of aerodynamic research with IR imaging: A survey

Infrared imaging used in aerodynamic research evolved during the last 25 years into a rewarding experimental technique for investigation of body-flow viscous interactions, such as heat flux determination and boundary layer transition. The technique of infrared imaging matched well its capability to produce useful results, with the expansion of testing conditions in the entire spectrum of wind tunnels, from hypersonic high-enthalpy facilities to cryogenic transonic wind tunnels. With unique achievements credited to its past, the current trend suggests a change in attitude towards this technique: from the perception as an exotic, project-oriented tool, to the status of a routine experimental procedure.

Gartenberg, Ehud↗
NASA NTRS1991

Problems and solutions for transition detection in cryogenic wind tunnels by infrared imaging

The authors analyzed the problems associated with the detection of boundary-layer transition to turbulence by using the IR imaging techique in cryogenic wind-tunnel testing. It is shown that testing at low temperatures forces this implementation to run against the physical laws of diminishing returns. The most difficult obstacle resulted from the considerable decrease in the overall level of IR radiation and the parallel shift of the bulk of the radiated energy to longer wavelengths, beyond 30 microns at 100 K. Some measures to alleviate the problem are described. The thermal signature of transition can be enhanced by allowing the flow in the wind tunnel to heat incrementally, thus inducing a transient heat transfer to the model. As a result, the model area under the turbulent regime is revealed by its higher heating rate compared to the laminar regime.

Gartenberg, Ehud↗
NASA NTRS1990

Transition detection studies in the cryogenic environment

Boundary-layer transition detection studies were carried out in the 0.3 Meter Transonic Cryogenic Tunnel on a supercritical airfoil, using an infrared imaging system. The purpose of the experiments was to determine the extent of the temperature range in which commercially available IR systems can detect transition in cryogenic environment. The experiment was designed to take advantage of a combination of factors including the wind tunnel operation mode, the model construction materials and the IR system image processing options. During the initial phases of the study, the IR based findings were confirmed by measurements done with a micro-thin hot-film system. Ultimately, free and forced transition could be detected down to 170 K.

Gartenberg, Ehud↗
NASA NTRS1990

Influence of temperature gradients on the measurement accuracy of IR imaging systems

Implementing a new experimental aerodynamic technique, a long electrically heated wire was placed across flows with general velocity distributions (wakes, jets). By measuring the temperature distribution along the wire with an IR camera, the flow behavior was identified. Furthermore, it is suggested that by using Nusselt number correlations, the velocity distributions can be deduced. Comparing the results with predictions based on heat transfer correlations, it was found that the IR camera cannot accurately track high gradient temperature fields. A correction procedure is outlined to account for the errors found in the measured results.

Gartenberg, Ehud↗
NASA NTRS1989

Infrared imaging and tufts studies of boundary layer flow regimes on a NACA 0012 airfoil

A study of boundary-layer flow regimes on a NACA 0012 airfoil from zero angle of attack up to separation is presented. The boundary-layer transition from the laminar to the turbulent regime and the onset of the separation were detected by surface thermography of the airfoil performed with an infrared imaging system. The findings were compared with observations of aluminum-foil tufts visible with the infrared imaging system. This arrangement allows the infrared imaging system to assume the dual role of flow regime detection through surface thermography and flow visualization through the observation of the aluminum-foil tufts. Ultimately the temperature history on an uncontaminated surface could provide an interpretation of the state of boundary-layer flow. Separation studies performed on the NACA 0012 airfoil showed that aluminum foil tufts can be observed with infrared imaging systems.

Gartenberg, Ehud↗
NASA NTRS1988

Phenomenological aspects of infrared imaging in aeronautical research

The various factors leading to obtaining a thermography of an aerodynamic body of interest using an infrared imaging camera are scrutinized. Included is a description of how the various heat transfer mechanisms determine the final surface temperature that may be time dependent even for steady state flows. Some constraining factors of the camera are also discussed. Finally, a method is outlined showing how the infrared imaging of aerodynamic configurations may ultimately evolve as a computational fluid dynamics code validation tool.

Gartenberg, Ehud↗
NASA NTRS1988

Aerodynamic investigation by infrared imaging

Infrared imaging systems can be used to measure temperatures of actively heated bodies immersed in an airstream. This monitoring of the convective heat transfer process, provides also information about the interaction between the body and the flow. The concept appeals to Nusselt/Reynolds numbers relations in order to produce data of interest from surface temperatures. Two test cases are presented and reference is made to analytical results: the mapping of a laminar jet and the temperature distribution along a constant power heated flat plate in laminar boundary layer regime. Although this research is currently focused on low speed aerodynamics, the extension to high speed aerodynamics, where the body undergoes frictional heating is of interest in this context, too.

Roberts, A. Sidney, Jr.↗
NASA NTRS1987

Infrared surface imaging as a flowfield diagnostic tool

An infrared imaging system supported by a dedicated image processing system was evaluated as a diagnostic tool for aerodynamic research. Results are reported characterizing the system's capability for performing a variety of experimental investigations, such as temperature transients, air velocity distributions, capture of vortices, boundary layer flows, and separated flows over a flat plate with a two-dimensional rearward-facing step.

Gartenberg, Ehud↗