PIV flow measurements for a rotating square smooth channel heated by basically uniform heat flux

This document is the Accepted Manuscript of the following article: Ruquan You, Haiwang Li, Hongwei Wu, and Zhi Tao, ‘PIV flow measurements for a rotating square smooth channel heated by basically uniform heat flux’, International Journal of Heat and Mass Transfer, Vol. 119: 236-246, April 2018. Under embargo until 22 December 2018. The final, definitive version is available online at DOI: https://doi.org/10.1016/j.ijheatmasstransfer.2017.11.073, published by Elsevier Ltd.In this paper, we experimentally investigated the mainstream and secondary flow in a smooth rotating channel with wall heated by particle image velocimetry (PIV). The hybrid effect of Coriolis force and buoyancy force on the mainstream and secondary flow was taken into consideration in the current work. In the experiments, the Reynolds number, based on the channel hydraulic diameter (D = 80 mm) and the bulk mainstream velocity (Vm = 1.82 m/s), is 10,000, and the rotation numbers are 0, 0.13, 0.26, 0.39, respectively. Constant heat flux on the four channel walls are provided by Indium Tin Oxide (ITO) heater glass, the density ratio (d.r.) equaling approximately 0.1. The buoyancy number ranges from 0 to 0.153. The results showed that Coriolis force and buoyancy force have important influences on the flow field in rotating channels. Coriolis force pushes the mainstream to trailing side, making an asymmetry of the mainstream. On the cross-section, there is a symmetric two-vortex pair caused by the Coriolis. The two-vortex pair is pushed into the trailing side with the increase of rotation numbers. Then, there are two small vortex appearing near the leading side. Buoyancy force suppresses mainstream and causes the separation of the flow near the leading side. When the separated flow happened, the structure of secondary flow is disordered near the leading side.Peer reviewedFinal Accepted Versio

EXPERIMENTAL INVESTIGATION OF INTERNAL COOLING PASSAGES ON GAS TURBINE BLADE WITH PIN-FINS AND RIB-TURBULATORS

Heat transfer and pressure characteristics in a rectangular channel are experimentally explored in detailed. The study consisted of 3 parts: 1) effects of detached pin space, 2) combined effects of detached pin space and ribs, and 3) effects of pin-fin geometry on heat transfer. The overall channel geometry (W=76.2 mm, E=25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D=6.35 mm= ¼E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the un-obstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Pressure drop of each test case is also measured in order to evaluate the performance of each case based on a non-dimensional parameter, performance index, PI. Experimental results reveal that the presence of a detached space between the pin-tip and the endwall have a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D leads to lower heat transfer enhancement and pressure drop. Addition of broken ribs and full ribs has significant impact on heat transfer enhancement at the endwall only. Due to the geometry of the ribs, that is relatively low as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. Results showed that ribs underperform as compared to the cases without ribs. Triangular pin-fins with sharp edges have the advantages of generating additional wakes and vortices compared to circular and semi-circular pin-fins which contribute to higher heat transfer at the downstream region. However, heat transfer at the leading region of the triangular pin-fins are lower due to a more streamlined geometry at the leading region and without the presence of horseshoe vortices, that is one of the major contributing factors of heat transfer enhancement for circular and semi-circular pin-fins. Having the largest number of pin-fins and arranged in a dense configuration, the TRI3 case has the highest overall heat transfer enhancement ranging between 3.5-3.8, that is approximately 5%-20% higher than that of the circular pin-fin array. As the TRI1 and TRI2 cases show comparable heat transfer enhancement, this suggests that the heat transfer performance of the triangular pin-fin arrays is insensitive to the transverse spacing. In addition, more uniform heat transfer is also observed on the endwall and neighboring pin-fins in all triangular shaped pin-fin arrays. The semi-circular pin-fin array has the lowest heat transfer performance ranging from 2.7-3.4. However, triangular pin-fin arrays give the highest pressure loss due to the largest induced form drag among all cases, while circular pin-fin array exhibits the lowest pressure loss

Analysis of Heat Transfer on Turbulence Generating Ribs using Dynamic Mode Decomposition

Ducts with turbulence-promoting ribs are common in heat transfer applications. This study uses a recent modal extraction technique called Dynamic Mode Decomposition (DMD) to determine mode shapes of the spatially and temporally complex flowfield inside a ribbed duct. One subject missing from current literature is a method of directly linking a mode to a certain engineering quantity of interest. Presented is a generalized methodology for producing such a link utilizing the data from the DMD analysis. Theory suggests exciting the modes which are identified may cause the flow to change in such a way to promote the quantity of interest, in this case, heat transfer. This theory is tested by contouring the walls of the duct by the extracted mode shapes. The test procedure is taken from an industrial perspective. An initial, unmodified geometry provides a baseline for comparison to later contoured models. The initial case is run as a steady-state Reynolds-Averaged Navier-Stokes model. Large-Eddy Simulation generates the necessary data for the DMD analysis. Several mode shapes extracted from the flow are applied to the duct walls and run again in the RANS model, then compared to the baseline, and their relative performance examined

Effect of Vibration on Retention Characteristics of Screen Acquisition Systems

An analytical and experimental investigation of the effect of vibration on the retention characteristics of screen acquisition systems was performed. The functioning of surface tension devices using fine-mesh screens requires that the pressure differential acting on the screen be less than its pressure retention capability. When exceeded, screen breakdown will occur and gas-free expulsion of propellant will no longer be possible. An analytical approach to predicting the effect of vibration was developed. This approach considers the transmission of the vibration to the screens of the device and the coupling of the liquid and the screen in establishing the screen response. A method of evaluating the transient response of the gas/liquid interface within the screen was also developed

Aeronautical Engineering: A special bibliography with indexes, supplement 74

This special bibliography lists 295 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1976

Computation of heat transfer in turbine rotor blade cooling channels with angled rib turbulators

The effects of rotation and Reynolds number on heat transfer in rotating two-pass square and rectangular channels with smooth walls and walls with 45 degree angled and V-shaped rib turbulators were investigated numerically using an unstructured, incompressible, Reynolds-averaged Navier-Stokes flow solver. The influence of 45 degree angled ribs and channel orientation on the local Nusselt number ratios for leading and trailing surfaces in a two-pass square channel (AR=1) are compared to experimental data for Reynolds numbers from 5,000 to 25,000 and dimensionless rotation numbers from 0.0 to 0.118. The influence of V-shaped ribs and channel orientation on the local Nusselt number ratios for leading and trailing surfaces in a two-pass rectangular channel (AR=2) are compared to experimental data for Reynolds numbers from 5,000 to 40,000 and rotation numbers from 0.0 to 0.210. It is concluded that rotation causes significant changes to the local Nusselt number ratio distribution relative to stationary conditions. Generally, the first pass trailing and second pass leading surfaces have increased local Nusselt number ratios due to the secondary ow impingement induced by rotation. Alternatively, the first pass leading and second pass trailing surface Nusselt number ratios tend to decrease with increased rotation

The influences of V-shaped ribs and spanwise system rotation on a turbulent square duct flow

In this thesis, the effects of surface-mounted V-shaped ribs and spanwise system rotations on fully-developed turbulent square duct flows were investigated using the particle image velocimetry (PIV) measurement, large-eddy simulation (LES) and direct numerical simulation (DNS). The PIV measurements were conducted in a water channel, and three different angled V-shaped (60°, 45° and 30°) and perpendicular (90°) ribs were considered. As a complement for the PIV experiments, LES was also used to simulate the measured cases under the same experimental conditions. To perform LES, a parallel finite volume method (FVM) code adopting the generalized curvilinear coordinate system was developed. The first- and second-order moments of the turbulence flows obtained from LES were validated against the PIV measurement data. Both the PIV and LES results showed that strong secondary flows in the pattern of a pair of counter-rotating streamwise-elongated vortices exist in all three V-shaped rib cases. The impacts of rib geometry on turbulent coherent structures were investigated using vortex identifiers, temporal autocorrections, spatial two-point autocorrelations, and velocity spectra. To study the effects of system rotations on turbulent square duct flows, DNS was performed for the turbulent flows confined within a square duct subjected to at a wide range of spanwise system rotations. The DNS was conducted using a modified open-source parallel spectral-element method (SEM) code. The influences on turbulent duct flows by the system rotation were investigated by analyzing the transport equations of Reynolds stresses and vorticity correlations. Turbulent structures under different system rotations were also systematically studied using the energy spectra, autocorrelations of vorticity fluctuations, and linear stochastic estimation. It was observed that in response to the system rotation, secondary flows appear as streamwise counter-rotating vortices. At sufficiently high rotation numbers, a Taylor-Proudman region appears and complete laminarization is almost reached near the top and sidewalls. It was also observed that the Coriolis force dominates the transport of Reynolds stresses and turbulent kinetic energy, and forces the spectra of streamwise and vertical velocities to synchronize within a wide range of streamwise length scales.February 201

Propfan Test Assessment (PTA)

The objectives of the Propfan Test Assessment (PTA) Program were to validate in flight the structural integrity of large-scale propfan blades and to measure noise characteristics of the propfan in both near and far fields. All program objectives were met or exceeded, on schedule and under budget. A Gulfstream Aerospace Corporation GII aircraft was modified to provide a testbed for the 2.74m (9 ft) diameter Hamilton Standard SR-7 propfan which was driven by a 4475 kw (600 shp) turboshaft engine mounted on the left-hand wing of the aircraft. Flight research tests were performed for 20 combinations of speed and altitude within a flight envelope that extended to Mach numbers of 0.85 and altitudes of 12,192m (40,000 ft). Propfan blade stress, near-field noise on aircraft surfaces, and cabin noise were recorded. Primary variables were propfan power and tip speed, and the nacelle tilt angle. Extensive low altitude far-field noise tests were made to measure flyover and sideline noise and the lateral attenuation of noise. In coopertion with the FAA, tests were also made of flyover noise for the aircraft at 6100m (20,000 ft) and 10,668m (35,000 ft). A final series of tests were flown to evaluate an advanced cabin wall noise treatment that was produced under a separate program by NASA-Langley Research Center

Study of the Effect of a Novel Dimensionless Parameter -- the Centrifugal Work Number(CW), on Spanwise Rotating channel Low-speed Compressible Flow

In the study of similarity of rotating channel flow, we found that the flow obtained from the enlarged model under the theory of incompressible rotation similarity (maintaining geometric similarity and the same Reynolds number, rotation number, Prandtl number and buoyancy number) differs significantly from the flow inside the original channel. Through theoretical derivation and dimensional analysis, we discovered another significant parameter -- the centrifugal work number(CW), which characterizes the ratio of centrifugal work to gas enthalpy in the rotating channel and is an important parameter for measuring the compressibility of fluids inside the rotating channel. Moreover, we have verified the effect of the centrifugal work ratio on the flow state of the rotating channel using numerical methods, further improving the similarity theory of rotating channel compressible flow.Comment: 16 pages, 6 figure

Large Eddy Simulations of complex turbulent flows

In this dissertation a solution methodology for complex turbulent flows of industrial interests is developed using a combination of Large Eddy Simulation (LES) and Immersed Boundary Method (IBM) concepts. LES is an intermediate approach to turbulence simulation in which the onus of modeling of “universal” small scales is appropriately transferred to the resolution of “problem-dependent” large scales or eddies. IBM combines the efficiency inherent in using a fixed Cartesian grid to compute the fluid motion, along with the ease of tracking the immersed boundary at a set of moving Lagrangian points. Numerical code developed for this dissertation solves unsteady, filtered Navier-Stokes equations using high-order accurate (fourth order in space) finite difference schemes on a staggered grid with a fractional step approach. Pressure Poisson equation is solved using a direct solver based on a matrix diagonalization technique. Second order accurate Adams-Bashforth scheme is used for temporal integration of equations. Dynamic mixed model (DMM) is used to model subgrid scale (SGS) terms. It can represent large scale anisotropy and back-scatter of energy from small-to-large scale through scale-similar term and maintain the energy drain through eddy viscosity term whose coefficient is allowed to change with in the computational domain. This code is validated for several bench-mark problems and is demonstrated to solve complex moving geometry problem such as stator-rotor interaction. A number of parametric studies on jets-in-crossflow are performed to understand complex fluid dynamics issues pertaining to film-cooling. These studies included effects of variation of hole-aspect ratio, jet injection angle, free-stream turbulence intensity and free-stream turbulence length scales on the coherent structure dynamics for jets-in-crossflow. Fundamental flow physics and heat transfer issues are addressed by extracting coherent structures from time-dependent three dimensional flow fields of film-cooling by inclined jet and studying their influence on the film-cooled surface heat transfer. A direct method to perform heat transfer calculations in periodic geometries is proposed and applied to internal cooling in rotating ribbed duct. Immersed boundary method is used to render complex geometry of trapped vortex combustor on Cartesian grid and fluid mixing inside trapped vortex cavity is studied in detail