Engineering topics

Hepner, Timothy E.

Publications and source records attributed to Hepner, Timothy E..

11 records

NASA NTRS2007

Experimental Evaluation of an Isolated Synthetic Jet IN Crossflow

The second case for this workshop builds upon the isolated synthetic jet of Case 1 by adding a crossflow, with no streamwise pressure gradient, for the developing jet to interact with. Formally, Case 2 examines the interaction of a single, isolated, synthetic jet and a fully turbulent zero-pressure gradient boundary layer. The resulting flow has many of the characteristics that need to be modeled with fidelity if the results of the calculations are to serve as the basis for research and design with active flow control devices. These include the turbulence in the boundary layer, the time-evolution of the large vortical structure emanating from the jet orifice and its subsequent interaction with and distortion by the boundary layer turbulence, and the effect of the suction cycle on the boundary layer flow. In a synthetic jet, the flow through the orifice and out into the outer flowfield alternates between an exhaust and a suction cycle, driven by the contraction and expansion of a cavity internal to the actuator. In the present experiment, the volume changes in the internal cavity are accomplished by replacing one of the rigid walls of the cavity, the wall opposite the orifice exit, with a deformable wall. This flexible wall is driven by a bottom-mounted moveable piston. The piston is driven electro-mechanically. The synthetic jet issues into the external flow through a circular orifice. In the present experiment, this orifice has a diameter of 0.250 inches (6.35 mm). The flow is conceptually similar to that documented in Schaeffler [1]. To document the flow, several measurement techniques were utilized. The upstream boundary conditions (in-flow conditions), and several key phase-averaged velocity profiles were measured with a 3-component laser-Doppler velocimetry system. Phase-averaged velocity field measurements were made with both stereo digital particle image velocimetry and 2-D digital particle image velocimetry as the primary measurement system. Surface pressure measurements were made utilizing an electronically scanned pressure system.

Schaeffler, Norman W.↗

NASA NTRS2004

LDV Surveys Over a Fighter Model at Moderate to High Angles of Attack

The vortex flowfield over an advanced twin-tailed fighter configuration was measured in a low-speed wind tunnel at two angles of attack. The primary test data consisted of 3-component velocity surveys obtained using a Laser Doppler Velocimeter. Laser light sheet and surface flow visualization were also obtained to provide insight into the flowfield structure. Time-averaged velocities and the root mean square of the velocity fluctuations were obtained at two cross-sections above the model. At 15 degrees angle of attack, the vortices generated by the wing leading edge extension (LEX) were unburst over the model and passed outboard of the vertical tail. At 25 degrees angle of attack, the vortices burst in the vicinity of the wing-LEX intersection and impact directly on the vertical tails. The RMS levels of the velocity fluctuations reach values of approximately 30% in the region of the vertical tails.

Sellers, William L., III↗

NASA NTRS2002

Overview of Active Flow Control Actuator Development at NASA Langley Research Center

The paper provides an overview of the actuator development work that is currently underway at NASA Langley Research Center in the context of some of the Active Flow Control research being conducted at NASA Langley. The actuator development effort has provided a focused, centralized location for this work within NASA Langley. The multidisciplinary team approach utilized in this effort has allowed input from multiple disciplines on how various actuator challenges can be addressed and has lead to some unique approaches in actuation.

Schaeffler, Norman W.↗

NASA NTRS1999

Aerodynamic Flow Field Measurements for Automotive Systems

The design of a modern automotive air handling system is a complex task. The system is required to bring the interior of the vehicle to a comfortable level in as short a time as possible. A goal of the automotive industry is to predict the interior climate of an automobile using advanced computational fluid dynamic (CFD) methods. The development of these advanced prediction tools will enable better selection of engine and accessory components. The goal of this investigation was to predict methods used by the automotive industry. To accomplish this task three separate experiments were performed. The first was a laboratory setup where laser velocimeter (LV) flow field measurements were made in the heating and air conditioning unit of a Ford Windstar. The second involved flow field measurements in the engine compartment of a Ford Explorer, with the engine running idle. The third mapped the flow field exiting the center dashboard panel vent inside the Explorer, while the circulating fan operated at 14 volts. All three experiments utilized full-coincidence three-component LV systems. This enabled the mean and fluctuating velocities to be measured along with the Reynolds stress terms.

Hepner, Timothy E.↗

NASA NTRS1992

Three-Component Laser Velocimetry Of Complex Flows

Since aeronautical research community depends on computations, to extent that predictions of flow-field behavior used without supporting data, question arises whether predictions of complex flow fields represent real world. In experiment, laser velocimetry used to validate computed predictions of complex flow fields. Results demonstrated capabilities of orthogonal three-component laser velocimeter to obtain data necessary to validate computational codes used.

Meyers, James F.↗

NASA NTRS1990

Investigation of Particle Sampling Bias in the Shear Flow Field Downstream of a Backward Facing Step

The flow field about a backward facing step was investigated to determine the characteristics of particle sampling bias in the various flow phenomena. The investigation used the calculation of the velocity:data rate correlation coefficient as a measure of statistical dependence and thus the degree of velocity bias. While the investigation found negligible dependence within the free stream region, increased dependence was found within the boundary and shear layers. Full classic correction techniques over-compensated the data since the dependence was weak, even in the boundary layer and shear regions. The paper emphasizes the necessity to determine the degree of particle sampling bias for each measurement ensemble and not use generalized assumptions to correct the data. Further, it recommends the calculation of the velocity:data rate correlation coefficient become a standard statistical calculation in the analysis of all laser velocimeter data.

Meyers, James F.↗

NASA NTRS1988

LDV surveys over a fighter model at moderate to high angles of attack

The vortex flowfield over an advanced twin-tailed fighter configuration has been studied in a low-speed wind tunnel at two angles of attack using LDV, along with laser light sheet and surface flow visualizations. At 15 deg angles of attack, the vortices generated by the wing leading edge extension (LEX) were found to be unburst over the model and to pass outboard of the vertical tail. At 25 deg angle of attack, the vortices were shown to burst in the vicinity of the wing-LEX intersection and to impact directly on the vertical tails.

Sellers, William L., III↗

NASA NTRS1988

Measurement of leading edge vortices from a delta wing using a three component laser velocimeter

A demonstration of the capabilities of a three-component laser velocimeter to provide a detailed experimental database of a complex flow field is presented. The orthogonal three-component laser velocimeter was used to measure the leading edge vortex flow field above a 75 deg delta wing at angles-of-attack of 20.5 deg and 40.0 deg. The resulting mean velocity and turbulence intensity measurements are presented. The laser velocimeter is described in detail including a description of the data processing algorithm. A full-error analysis was conducted and the results presented.

Meyers, James F.↗

NASA NTRS1988

Measurement of Leading Edge Vortices from a Delta Wing Using a Three Component Laser Velocimeter

A demonstration of the capabilities of a three component laser velocimeter to provide a detailed experimental database of a complex flow field i s presented. The orthogonal three component laser velocimeter was used to measure the leading edge vortex flow field above a 75 degrees delta wing at angles-of-attack of 20.5 degrees and 40.0 degrees. The resulting mean velocity and turbulence intensity measurements are presented. The laser velocimeter is described in detail including a description of the data processing algorithm. A full error analysis was conducted and the results presented.

Meyers, James F.↗

NASA NTRS1986

Measurement of leading edge vortices from a delta wing using a three component laser velocimeter

An investigation of the flow field above a 75-deg swept delta wing at a 20.5-deg angle of attack is described. The experiment was performed in the NASA Langley Basic Aerodynamic Research Tunnel (BART) using an orthogonal three-component laser velocimeter. Preliminary laser velocimeter results show velocity vectors in the cross flow plane at x/c = 0.5, revealing the formation of the primary and secondary vortices over the upper surface of the wing.

Meyers, James F.↗

NASA NTRS1984

Velocity Vector Analysis of a Juncture Flow Using a Three-Component Laser Velocimeter

A specialized single-axis, five-beam three-component laser velocimeter was constructed and used to study the flow field in a juncture. The juncture was defined by a blunt leading, edged vertical splitter plate and a sharp leading edged horizontal plate. The investigations were conducted in the Low Turbulence Pressure Tunnel at a Mach number of 0.1 and a Reynolds number of 2.2 x 10(exp 6) per meter over the model. The three-component velocity flow field in the juncture was measured, Reynolds stresses calculated and the velocity vector analysis performed.

Meyers, James F.↗