Showing papers in "International Journal of Rotating Machinery in 1996"

Film Cooling from a Single Row of Compound Angle Holes at High Blowing Ratios

Abstract: Experimental results are presented which describe the development and structure of flow downstream of a single row of holes with compound angle orientations producing film cooling at high blowing ratios. This film cooling configuration is important because similar arrangements are frequently employed on the first stage of rotating blades of operating gas turbine engines. With this configuration, holes are spaced 6d apart in the spanwise direction, with inclination angles of 24 degrees, and angles of orientation of 50.5 degrees. Blowing ratios range from 1.5 to 4.0 and the ratio of injectant to freestream density is near 1.0. Results show that spanwise averaged adiabatic effectiveness, spanwise-averaged iso-energetic Stanton number ratios, surveys of streamwise mean velocity, and surveys of injectant distributions change by important amounts as the blowing ratio increases. This is due to injectant lift-off from the test surface just downstream of the holes.

Dynamic Analysis of Composite Rotors

Abstract: An outline of formulation based on a layerwise beam theory for unbalance response and stability analysis of a multi mass, multi bearing composite rotor mounted on fluid film bearings is presented. Disc gyroscopics and rotary inertia effects are accounted for. Material damping is also taken into account. The layerwise theory is compared with conventionally used equivalent modulus beam theory. Some interesting case studies are presented. The effect of various parameters on dynamic behavior and stability of a composite rotor is presented.

A Small Perturbation CFD Method for Calculation of Seal Rotordynamic Coefficients

Abstract: Seal rotordynamic coefficients link the fluid reaction forces to the rotor motion, and hence are needed in the stability calculations for the overall rotating systems. Presented in this paper is a numerical method for calculations of rotordynamic coefficients of turbomachinery seals with rotors nominally at centered, eccentric and/or misaligned position. The rotor of the seal is assumed to undergo a prescribed small whirling motion about its nominal position. The resulting flow variable perturbations are expressed as Fourier functions in time. The N-S equations are used to generate the governing equations for the perturbation variables. Use of complex variables for the perturbations renders the problem quasi-steady. The fluid reaction forces are integrated on the rotor surface to obtain the fluid reaction forces at several different whirl frequencies. The rotordynamic coefficients are calculated using appropriate curve fitting. Details of the model are presented, and sample results for concentric and eccentric annular incompressible flow seals are included to demonstrate the capability and accuracy of the proposed method.

Prandtl Number Effects on Mixed Convection Between Rotating Coaxial Disks

Abstract: Prandtl number characterizes the competition of viscous and thermal diffusion effects and, therefore, is an influential factor in thermal-fluid flows. In the present study, the Prandtl number effects on non-isothermal flow and heat transfer between two infinite coaxial disks are studied by using a similarity model for rotation-induced mixed convection. To account for the buoyancy effects, density variation in Coriolis and centrifugal force terms are considered by invoking Boussinesq approximation and a linear density-temperature relation. Co-rotating disks (Ω2=Ω1) and rotor-stator system (Ω1≠Ω2=0) are considered to investigate the free and mixed convection flows, respectively. For Reynolds number, Re, up to 1000 and the buoyancy parameter, B=βΔT, of the range of |B|≤0.05, the flow and heat transfer characteristics with Prandtl numbers of 100, 7, 0.7, 0.1, and 0.01 are examined. The results reveal that the Prandtl number shows significant impact on the fluid flow and heat transfer performance. In the typical cases of mixed convection in a rotor-stator system with |B|=0.05, the effects in buoyancy-opposed flows B=0.05 are more pronounced than that in buoyancy-assisted ones.

Film Cooling from Two Staggered Rows of Compound Angle Holes at High Blowing Ratios

Abstract: Experimental results are presented which describe the development and structure of flow downstream of two staggered rows of film-cooling holes with compound angle orientations at high blowing ratios. These film cooling configurations are important because they are frequently employed on the first stage of rotating blades of operating gas turbine engines. With this configuration, holes are spaced 3d apart in the spanwise direction, with inclination angles of 24 degrees, and angles of orientation of 50.5 degrees. Blowing ratios range from 0.5 to 4.0 and the ratio of injectant to freestream density is near 1.0. Results show that spanwise averaged adiabatic effectiveness, spanwise-averaged iso-energetic Stanton number ratios, surveys of streamwise mean velocity, and surveys of injectant distributions change by important amounts as the blowing ratio increases. This is due to injectant lift-off from the test surface just downstream of the holes which becomes more pronounced as blowing ratio increases.

Influence of Bearing Defects on Dynamical Behavior of An Elastic Shaft

Abstract: A study of an elastic rotor supported by two defect bearings is presented. The bearing behavior must be considered non-linear because of the defect effects. The rotor is modelled by typical beam finite element including effects such as gyroscopic effect. The dynamic behavior is analysed using an unsteady time integration procedure. A modal technique is used to reduce the number of degrees of freedom. Results show that the bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non linear analysis.

Turbulence and Scale Measurements in a Square Channel with Transverse Square Ribs

Abstract: Hot-wire measurements of the mean flow, turbulence characteristics, and integral scale in a square channel roughened with transverse ribs mounted on two opposing sidewalls are presented for three rib configurations: single rib, in-line multiple ribs, and staggered multiple ribs. Test conditions for multiple ribs use p/H = 10, H/D 0.17, and Re⁡D 23,000. Measured results highlight the spatial distribution and evolution of turbulence intensity and integral scale from the flow entrance of the first period to the developed regime near the exit of the third period. The highly turbulent, shear layer initiated near the trailing upper-edge of a rib elevates the turbulence level in the mainstream of the channel. The magnitude of turbulence intensity in the channel core rises from 0.7% in the approaching flow to about 20–25% near the exit of the third period. The integral scale dominating the mainstream flow increases from approximately one-half the rib-height, 0.5H, in the approaching flow to 1.5-2.5H behind the first rib and further downstream.

Experimental Investigation of the Flow Field in a Multistage Axial Flow Compressor

Abstract: The nature of the flow field in a three stage axial flow compressor, including a detailed survey at the exit of an embedded stator as well as the overall performance of the compressor is presented and interpreted in this paper. The measurements include area traverse of a miniature five hole probe (1.07 mm dia) downstream of stator 2, radial traverses of a miniature five hole probe at the inlet, downstream of stator 3 and at the exit of the compressor at various circumferential locations, area traverse of a low response thermocouple probe downstream of stator 2, radial traverses of a single sensor hot-wire probe at the inlet, and casing static pressure measurements at various circumferential and axial locations across the compressor at the peak efficiency operating point. Mean velocity, pressure and total temperature contours as well as secondary flow contours at the exit of the stator 2 are reported and interpreted. Secondary flow contours show the migration of fluid particles toward the core of the low pressure regions located near the suction side casing endwall corner.

System Identification Methods for Dynamic Testing of Fluid-Film Bearings

Abstract: There are various system identification approaches typically used to extract the rotordynamic coefficients from simultaneously measured dynamic force and motion signals. Since the coefficient values extracted can vary significantly as a function of the system identification approach used, more attention is needed to treat this issue than is typically included in the rotor dynamics literature. This paper describes system identification and data reduction methods used for extracting rotordynamic coefficients of fluid-film journal bearings. Data is used from a test apparatus incorporating a double-spoolshaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirling. For example, a least squares linear regression on the force-displacement equations of the experiment provides only one of the rational approaches to extract the anisotropic rotordynamic coefficients (stiffness, damping and fluid inertia effects). Rotordynamic coefficients are also extracted with both first and second order orbital frequency dependencies. To assess the quality of the measured signals, coherence functions are calculated to relate the time-averaged input motion signals and the time-averaged output force signals.

Impeller Flow Field Laser Veloc meter Measurements

Abstract: Development of Computational Fluid Dynamics (CFD) computer codes for complex turbomachinery affords a complete three-dimensional (3-D) flow field description. While significant improvements in CFD have been made due to improvements in computers, numerical algorithms, and physical modeling, a limited experimental database for pump CFD code validation exists.

An Integrated Flow Analysis System for the Recalculation of Hydraulic Machinery Bladings

Abstract: The present paper deals with the recalculation of hydraulic machinery bladings. By combining numerical tools for the geometrical description of the bladings, mesh generation, different CFD flow models (Q3D Euler, 3D Euler, Navier-Stokes) and post-processing a highly efficient integrated flow analysis system is obtained.

Identification of the Quadrature Resonances UsingModal Nonsynchronous Perturbation Testing andDynamic Stiffness Approach for an Anisotropic RotorSystem with Fluid Interaction

Abstract: The paper presents the dynamic analysis of an anisotropic rotor system with fluid interaction by using modal nonsynchronous perturbation testing and dynamic stiffness approaches. The anisotropic rotor system produces more complex rotor behavior than an isotropic system. In particular, the existence of the quadrature resonance phenomenon for backward precession is demonstrated. A symmetric rotor supported anisotropically by one fluid lubricated bearing and one rolling element bearing simulates rotating machinery behavior. A dynamic stiffness anisotropy algorithm which includes fluid terms is used to process experimental data in order to identify lightly loaded journal fluid film force parameters. The existence of the quadrature resonance for backward precession obtained from the experiment is compared with the analytical model. The results from modeling show strong agreement with experimental results.

Effect of Upstream Wake on Shower-Head Film Cooling

Abstract: The present study aims to investigate the effect of an upstream wake on the convective transport phenomena over a turbine blade with shower-head film cooling. A naphthalene sublimation technique was implemented to obtain the detailed mass transfer distributions on both suction and pressure surfaces of the test blade. All mass transfer runs were conducted on a blowing-type wind tunnel with a six-blade linear cascade. The leading edge of the test blade was drilled with three rows of equally spaced injection holes. The upstream wake was simulated by a circular bar with the same diameter as that of the trailing edge of the test blade.