C. R. Truman

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement with Crossflow

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after impingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

High speed optical tomography system for imaging dynamic transparent media.

We describe the design and operation of a high speed optical tomography system for measuring two-dimensional images of a dynamic phase object at a rate of 5 kHz. Data from a set of eight Hartmann wavefront sensors is back-projected to produce phase images showing the details of the inner structure of a heated air flow. The tomographic reconstructions have a spatial resolution of approximately 2.0 mm and can measure temperature variations across the flow with an accuracy of about 0.7 C. Series of animated reconstructions at different downstream locations illustrate the development of flow structure and the effect of acoustic flow forcing.

Evaluation of algebraic turbulence models for PNS predictions of supersonic flow past a sphere-cone

Les previsions de Navier-Stokes parabolises sont comparees aux mesures pour des ecoulements adiabatiques a Mach 3 et des ecoulements sur paroi froide a Mach 5 et 8

Linear stochastic estimation of optical beam deflection through a heated jet

Linear stochastic estimation (LSE) is used to predict optical beam deflection based on temperatures measured in a heated round turbulent jet. An He-Ne laser beam was propagated through a dynamic refractive-index field created by a jet heated 15 C above ambient. Simultaneous measurements of beam deflection in the streamwise direction and temperature at four reference points along the path of the propagated beam were made. Acoustic excitation produced perturbations in the flow field at frequencies corresponding to one of the two dominant axisymmetric modes of instability (the shear layer and jet column modes) which induced vortex pairing and helped stabilize the passage of coherent structures at fixed streamwise positions. Various LSE strategies to predict the dynamic beam deflection (or jitter) were investigated. Good predictions of beam deflection were made by an LSE based on just four reference points that were judiciously selected. For this flow field, a four-point LSE based on time signals from two probes was able to predict optical beam jitter just as well as a four-point LSE using all four probes. These results may be applicable to adaptive optics systems or to turbulent flow control. (Author)

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.Copyright

Prediction of turbulent source flow between corotating disks with an anisotropic two-equation turbulence model

An anisotropic form of a low-Reynolds-number two-equation turbulence model has been implemented in a numerical solution for incompressible turbulent flow between corotating parallel disks. Transport equations for turbulent kinetic energy and dissipation rate were solved simultaneously with the governing equations for the mean-flow variables. Comparisons with earlier mixing-length predictions and with measurements are presented. Good agreement between the present predictions and the measurements of velocity components and turbulent kinetic energy was obtained. The low-Reynolds-number two-equation model was found to model adequately the near-wall region as well as the effects of rotation and streamline divergence, which required ad hoc assumptions in the mixing-length model.

Prediction of turbulent source flow between stationary and rotating discs

Abstract Results are presented from a numerical investigation of turbulent source flow between two discs, both of which are stationary or corotating. Parabolic flow was assumed and the Box Method used to obtain marching solutions of the governing equations. Turbulence modelling was based on extensions of classical eddy-viscosity/mixing-length concepts which reflect the influences of divergence of the mean-flow streamlines and non-isotropic Reynolds stresses due to disc rotation. The predictions for the rotating case are the first local results available. For the stationary case, earlier work has been extended by the use of empirical formulae for reverse transition and inclusion of the influence of streamline divergence. Comparisons with limited data for stationary and corotating discs show reasonable agreement. Although the turbulence models are probably not optimum, they provide an adequate basis for engineering studies of turbulent source flow between corotating and stationary discs until more extensive and reliable empirical information is available.

Optical tomographic study of the effect of excitation of a heated round jet

An optical tomography system has been used to examine the near-field flow characteristics of a round heated air jet. Tomographic reconstructions of instantaneous refractive-index (or temperature) fields in a plane normal to the jet axis are presented. High-speed sampling allows detailed reconstruction of the temperature field produced by organized structures in the flow. The tomographic reconstructions are compared with profiles of mean and fluctuating temperature obtained with conventional cold-wire anemometry. Acoustic excitation is used to enhance the formation of ring vortices. The effect of excitation upon the mean and fluctuating temperature profiles is revealed by examining the tomographic reconstructions. The influence of the excitation on vortex interaction, including pairing, was found to be significant, producing large differences in the detailed temperature distributions within the jets.

Noniterative Solution for Pressure in Parabolic Flows

Parabolic flows in which the pressure variation in the streamwise (or marching) direction is unknown a priori include internal thin shear layers, shock-boundary layer interactions, and inverse boundary layers with specified displacement thickness or shear stress. The pressure is typically obtained thorough an additional iteration beyond that required to determine the velocity components (and other dependent variables). A generalized block- tridiagonal procedure is discussed in which pressure is determined within the iteration for velocity components to substantially reduce computation time. The increase in algebraic complexity in the solution procedure is small; no increase in the size of the block matrices is required. The method applies to any marching solution in which a scalar dependent variable is constant across the flow, but varies in the streamwise or marching direction.

Open-loop control of compensation for optical propagation through a turbulent shear flow

A piezoelectric steering mirror was used to compensate for deflections of a thin laser beam induced by propagation through a turbulent jet. The mirror was controlled using Linear Stochastic Estimates (LSE) of beam deflection based on two temperature probes in the shear layer on one side of the jet. When the jet was excited in one of its fundamental modes, the periodicity of the large-scale vortex structure allowed compensation for more than 50% of the deflection produced by the jet. When no external forcing was imposed, the steering mirror was able to compensate for less than 20% of the deflection produced by the jet. The results indicate that open-loop control of adaptive optics systems is feasible with good estimates of optical degradation based on limited flowfield measurements. These measurements can include temperature or velocity data from selected points or oneor two-dimensional measurements based on Hartmann sensors.