An optimization method for three-dimensional turbine blade
design including end wall contouring control with
non-axis-symmetric geometry has been developed. This design
optimization method consists of three-dimensional parametric
modeling module for blades and end walls, optimization algorithm
module and the design evaluation method using Computational
Fluid Dynamics code.
This paper presents the advanced and more applicative study to
enhance this optimization methodology from a single turbine stage
to two turbine stages with stator blade hub leakage and rotor blade
tip leakage influences.
Results of present fluid dynamic design optimization study with
consideration of tip and hub leakage show that the efficiency of the
current well designed high pressure steam turbine stage has been
enhanced by 0.21%. Using parallel optimization algorithm and a
cluster PC system, the design cycle can be shortened to seven days
for an optimization with one thousand iterations of two turbine
stage CFD on 20 CPUs of 2.0G cluster PC.
Ingress occurs when hot mainstream gas from the turbine annulus is ingested through a rim seal into the wheel-space between a rotating turbine disc (the rotor) and an adjacent stationary casing (the stator). The stationary vanes and rotating blades in the annulus create circumferential variations of pressure that drive hot gas inwards into the wheel-space in regions of high external pressure. This is called externally-induced ingress. (The rotating flow in the wheel-space creates a radial pressure gradient that separately promotes radially inward flow into the wheel-space. This is known as rotationally-induced ingress). The high temperature of the ingested mainstream gas in an engine can lead to fatigue and damage to important components.
This paper describes simplified computational studies of externally-induced ingress into a rotor-stator system with an axial clearance rim seal. Axisymmetric steady-state computations are carried out using the commercial computational fluid dynamics code CFX. The SST model of turbulence is used. The model geometry and boundary conditions are based on an experimental rig designed and built at the University of Bath to study fundamental features of ingestion and rim seal effectiveness, in a related project having substantial industrial involvement. It is known that simplified steady flow models can significantly underestimate ingestion from the mainstream annulus into the wheel-space. In the present work, ingestion is prescribed in the steady model through the use of boundary conditions at the axial clearance seal. The computation of the flow and heat transfer in the wheel-space is validated by comparison with previously-published experimental measurements for a simple rotor-stator system without ingestion. The computations are carried out for values of rotational Reynolds number up to around 1.25 x 106 as typically used in
experimental studies, and using sealing air flow-rates corresponding to non-dimensional values relevant to engine applications.
The computed results show that the flow structure and heat transfer in the wheel-space at high sealing flow rates agree well with measured values for rotor-stator systems, the effects of differences between geometries being mostly small. Due to the recirculating secondary flow in the wheel-space, ingested fluid is drawn toward the surface of the stator. At lower sealing flow rates, the higher swirl of the ingested mainstream flow causes changes in the flow structure in the wheel-space. The ingested mainstream flow can come into contact with the rotor, and this could have serious consequences in practice.
This paper presents a heat transfer and details flowfield measurements
of multiple cooling holes. Normal cylindrical hole with
steeper inclined angle of 20° arranged to perform a 5 times 4
cooling holes matrix have been considered. Experiments have been
done at a single Reynolds number base on the hole diameter equal
to 6200 at three blowing ratios of 0.5, 1.0 and 2.0 for the heat
transfer and only for the later two for aerodynamics measurements.
The heat transfer experiments involved the IR camera to capture the
surface temperature data while the aerodynamics experiments
involved the three dimensional Laser Doppler Velocimeter for
velocity measurements. Results of heat transfer consists of overall
film cooling effectiveness distribution and laterally average film
cooling effectiveness in x-direction represented by a contour plot
and a graph respectively. Four measurement planes have been
considered in the aerodynamics experiments which are located at
x/D = 7, 17, 27 and 37. The aerodynamics results presented in this
paper include of various contour plots which represent the distribution
of normalize velocity for u, v, and w components, normalize
root mean square velocity for u, v, and w components and the
Reynolds stress tensor. Both set of results have been discussed in
such, a clear relation between the flow behavior and heat transfer
phenomena have been established.
The purpose of the present study is to clarify the heat transfer
characteristics with multiple jet impingement aiming at the highly
efficient cooling performance. In the study, we investigated the
effect of injection parameters on circular jet array impingement
heat transfer. As we focus on interference among the adjacent
impinging jets, tests are mainly conducted at the minimum
crossflow condition. The experiments are also conducted at
injection distance from 2 to 8 jet hole diameters and jet-to-jet
spacing from 4 to 8 jet hole diameters. Jet hole diameter Reynolds
number is 4,680. Thermochromic liquid crystal is used to obtain
heat transfer coefficient. Wall pressure measurement and oil flow
visualization on the target surface are performed to understand the
flow pattern of impinging jet and wall jet. The effect of injection
parameters, such as injection distance, jet-to-jet spacing and
number of jets, on jet array impingement heat transfer is clarified.
It is well known that asymmetric vane spacing can result in
decreased levels of the excitation at specific frequencies. In this
paper, the resonant response reduction of mistuned bladed disks
due to asymmetric vane spacing is studied theoretically for the most
probable asymmetric vane, in which the vane count of the upper
and lower half is slightly different. First, a method for predicting
the maximum amplitude of the mistuned bladed disk for the
asymmetric vane spacing is proposed. Second, a parametric study is
carried out using Monte Carlo simulation to clarify the vibration
response characteristics of the mistuned bladed disk for the
asymmetric vane spacing. From these results, it is concluded that
asymmetric vane spacing is effective for reduction of resonant
amplitudes of a mistuned bladed disk if a multi-resonance phenomenon
does not appear.
This study deals with the experimental and numerical studies of
the effect of free-stream turbulence on turbine blade leading edge
film cooling. The study examines several test cases with two
blowing ratios (BR=1.0 and 2.0) and three mainstream turbulence
intensities (1.0, 3.3 and 12.0 %) using two types of leading edge
models with cylindrical holes and diffuser holes . The leading
edge model consists of a semi-circular part of 80mm diameter and a
flat after-body. Film effectiveness and heat transfer coefficient on
the model surface are measured by the transient method using
thermochromatic liquid crystal with video camera. In addition,
detailed investigation of the film cooling is carried out using CFD
simulations. RANS approach using Shear Stress Transport turbulence
model was employed to solve the flow field. In the case of
diffuser hole, the effect of mainstream turbulence intensity appears
significantly, and spanwise averaged film effectiveness is decreased.