Numerical Calculation of Flow for Cascade With Tip Clearance

Three-dimensional incompressible turbulent flow within a linear turbine cascade with tip clearance is analyzed numerically. The governing equations involving the standard k-ε model are solved in the physical component tensor form with a boundary-fitted coordinate system. In the analysis, the blade tip geometry is treated accurately in order to predict the flow through the tip clearance in detail when the blades have large thicknesses. Although the number of grids employed in the present study is not enough because of the limitation of computer storage memory, the computed results show good agreements with the experimental results. Moreover, the results clearly exhibit the locus of minimum pressure on the rear part of the pressure surface at the blade tip.

Flow Field Investigation in the Exit Region of a Radial Inflow Turbine Using LDV

Detailed flow investigation in the downstream region of a radial inflow turbine has been performed using a three component Laser Doppler Velocimetry. The flow velocities are measured in the exit region of the turbine at off-design operating conditions. The results are presented as contour and vector plots of mean velocities, flow angles and turbulent stresses. The measured parameters are correlated to the rotor blade rotation to observe any periodic nature of the flow. The measurements reveal a complex flow pattern near the tip region at the rotor exit due to the interaction of the tip clearance flow. The degree of swirl of the flow near the tip region at the rotor exit is observed to be high due to the gross under turning of the flow near the tip region. The effect of the rotor on the exit flow field is observed in the proximity of the rotor exit.

Unsteady Boundary Layers on a Flat Plate Disturbed by Periodic Wakes: Part I — Measurement of Wake-Affected Heat Transfer and Wake-Induced Transition Model

Measurements of wake-affected heat transfer distributions on a flat plate are made by use of a wake generator that consists of a rotating disk and several types of circular cylinders. The main purpose of this study is to construct a wake-induced transition model in terms of an intermittency factor, considering the evolution of the wake-induced turbulent region, a so-called turbulent patch in a distance-time diagram. A comparison between the proposed transition model and the measured heat transfer data reveals that the transition model yields good agreement with the measured data of all test conditions in this study.

Computed Eccentricity Effects on Turbine Rim Seals at Engine Conditions With a Mainstream

A previously verified axisymmetric Navier-Stokes computer code was extended for three-dimensional computation of eccentric rim seals of almost any configuration. All compressibility and thermal/momentum interaction effects are completely, included, and the temperature, pressure and Reynolds number of the mainstream, coolant stream and turbine wheel are fixed at actual engine conditions. Regardless of the seal eccentricity, both ingress and egress are found between θ = −30° and 100°. which encompasses the location of maximum radial clearance at θ = 0°. All other θ locations within the rim seal show only egress, as does the concentric basecase for all circumferential locations. Further, the maximum ingress occurs near θ = 30° for all eccentricities. This is found to produce a blade root/retainer temperature rise from the concentric case of 390 percent at 50 percent eccentricity and a 77 percent rise at 7.5 percent eccentricity. In addition, the nature of an increased eccentricity causing a decreased seal effectiveness is examined, along with the corresponding increase of cavity-averaged temperature.

An Experimental and Computational Investigation of Flow in a Radial Inlet of an Industrial Pipeline Centrifugal Compressor

The flowfield of a complex three dimensional radial inlet for an industrial pipeline centrifugal compressor has been experimentally determined on a half scale model. Based on the experimental results, inlet guide vanes have been designed to correct pressure and swirl angle distribution deficiencies. The unvaned and vaned inlets are analyzed with a commercially available fully 3D viscous Navier-Stokes code. Since experimental results were available prior to the numerical study, the unvaned analysis is considered a postdiction while the vaned analysis is considered a prediction. The computational results of the unvaned inlet have been compared to the previously obtained experimental results. The experimental method utilized for the unvaned inlet is repeated for the vaned inlet and the data has been used to verify the computational results. The paper will discuss experimental, design and computational procedures, grid generation, boundary conditions, and experimental versus computational methods. Agreement between experimental and computational results is very good, both in prediction and postdiction modes. The results of this investigation indicate that CFD offers a measurable advantage in design, schedule and cost and can be applied to complex, three dimensional radial inlets.

Numerical Simulation of 3D Viscous Flow in a Linear Compressor Cascade With Tip Clearance

A Navier-Stokes solver is applied to investigate the 3D viscous flow in a low speed linear compressor cascade with tip clearance at design and off-design conditions with two different meshes. The algebraic turbulence model of Baldwin-Lomax is used for closure. Relative motion between the blades and wall is simulated for one flow coefficient. Comparisons with experimental data, including flow structure, static and total pressures, velocity profiles, secondary flows and vorticity, are presented for the stationary wall case. It is shown that the code predicts well the flow structure observed in experiments and shows the details of the tip leakage flow and the leading edge horseshoe vortex.

Numerical Study of the Internal Flow Field of a Centrifugal Impeller

The complex three-dimensional flow field in a centrifugal impeller with low speed is studied in this paper. Coupled with high–Reynolds–number k–ε turbulence model, the fully three–dimensional Reynolds averaged Navier–Stokes equations are solved. The Semi–Implicit Method for Pressure–Linked Equations (SIMPLE) algorithm is used. And the non–staggered grid arrangement is also used. The computed results are compared with the available experimental data. The comparison shows good agreement.

Numerical Investigation of Unsteady Incompressible 3D Turbulent Flow and Torque Transmission in Fluid Couplings

The adequate understanding of the flow structure in fluid couplings is necessary for the optimized design of such devices. Up to now, empiricism plays an important role in design. Detailed studies of the unsteady 3D flow and torque transmission in fluid couplings were rarely carried out. In this paper the unsteady Reynolds time-averaged Navier-Stokes equations coupled with the k-ε model have been solved by a finite-volume method. The calculations were done by using boundary-fitted grids with non-staggered variable arrangement for a rotating frame of reference. Flow structures in fluid couplings were obtained. The results give insights into the physical process of torque transmission. A comparsion of the calculated torque transimission with the experimental measurements in the literature shows good agreement for low slip.

Modelling of By-Pass Transition With Conditioned Navier-Stokes Equations and a K-E Model Adapted for Intermittency

Turbomachinery flows are characterized by a very high intensity turbulent mean part. As a consequence, laminar flow in boundary layer regions undergoes transition through direct excitation of turbulence. This is the so-called bypass transition. Regions form that are intermittently laminar and turbulent. In particular in accelerating flows, as on the suction side of a turbine blade, this intermittent flow can extend over a very large part of the boundary layer. Classical turbulence modelling based on global time averaging is not valid in intermittent flows. To take correctly account of the intermittency, conditioned averages are necessary. These are averages taken during the fraction of time the flow is turbulent or laminar respectively. Starting from the Navier-Stokes equations, conditioned continuity, momentum and energy equations are derived for the laminar and turbulent parts of an intermittent flow. The turbulence is described by the classical k-ε model. The supplementary parameter introduced by the conditioned averaging is the intermittency factor. In the calculations, this factor is prescribed in an algebraic way.

On the Use of Direct and Inverse Numerical Flow Calculations for Supersonic Turbine Design

A procedure for blade design, using a time marching method to solve the Euler equations in the blade-to-blade plane is presented. This procedure uses an Office Nationale d’Etude et de Recherches Aeronautique flow solver. The classical slip conditions (no normal velocity component along the blade profile) has been replaced by another boundary conditions in such a way that the required pressure may be imposed directly. The orignal direct code was therefore transformed into an inverse solver. The unknows are calculated on the blade wall using the so-called compatibility relations. The blade geometry is then modified by resetting the wall parallel to the new flow field. The results obtained with this design process for a supersonic turbine blade of a space turbopump is presented.