The present invention relates to turbine blades for turbomachinery such as gas turbine engines and, more particularly, to improved geometrical shapes for such blades and the platform from which they extend.
Turbine blades are mounted circumferentially on an inner diameter platform about a turbine shaft to allow rotation thereof in streams of working medium fluids to extract energy and work therefrom as those fluids flow around and past such blades through the flow passages between them. Such flows can be transonic in accelerating from below the speed of sound coming into the blade region to being above the speed of sound in the exit region. In these situations inefficiencies due to shock wave losses are important.
Blade airfoil surface profiles and the geometry of the airfoil and the platform on which the blade is mounted become very important in achieving high efficiencies. In addition, a blade design to be suitable must minimize the penalties imposed on the engine system by the weight and cost of the blades, and need for cooling air therein, a goal sought through reducing the number of blades provided about the platform circumference for each blade stage used. However, the remaining blades must then extract more work, the lift or loading of the blade, from the fluid streams passing thereby which tends to reduce blade efficiency. A high lift blade will have a Zweifel lift coefficient (the ratio of the actual load to the ideal load) that is greater than 1.1. Thus, there is a desire for a blade that achieves high efficiency during transonic operation while having a large lift loading.
The present invention provides a turbine blade system including a blade airfoil having an airfoil shape with the blade airfoil having a nominal profile substantially in accordance with normalized Cartesian coordinate values of X, Y and Z set forth in Table 1 below and which values are dimensionless values that are convertible to corresponding absolute distance values through manipulating them in accord with corresponding normalization equations. The X and Y absolute distance values, when connected by smooth continuing arcs, define nominal airfoil profile sections at each Z absolute distance value, and these nominal airfoil profile sections, when joined smoothly with adjacent ones thereof, form a complete nominal airfoil shape that is substantially matched by the airfoil shape of the blade airfoil. This blade airfoil can be supported on a ring platform having a support surface with a support surface shape in the vicinity of the location at which that blade airfoil is supported thereon such that the support surface smoothly joins with the airfoil shape of that blade airfoil, the support surface having a nominal profile substantially in accordance with normalized Cartesian coordinate values of X, Y and Z set forth in Table 4 below and which values are dimensionless values that are convertible to corresponding absolute distance values through manipulating them in accord with corresponding normalization equations, and wherein X and Y absolute distance values at various Z absolute distance values, when connected by smooth continuing arcs, form a nominal support surface shape substantially matched by the support surface shape of the support surface.
Blade 10 and the inner diameter 12 surface of the platform on which blade 10 is mounted of the present invention are shown in the pictorial perspective view of
Zweifel=[(1/g)*{dot over (m)}*ΔCu]/[0.5*ρ*W2̂2*bx*h]
where:
g=acceleration due to gravity of 32.2 ft/s2
{dot over (m)}=mass flow (lbm/s)
ΔCu=Cu2−Cu1=change in tangential velocity across the blade (ft/s)
ρ=density (lbm-s2/ft4)
W2=exit relative velocity (ft/s)
bx=axial chord (ft)
h=span (ft)
A perspective diagram of the blade of
Some definitions of terms used in the description include the leading edge as blade or airfoil point farthest toward the forward direction of the engine and the trailing edge as blade or airfoil point farthest toward the rearward from the forward direction of the engine. The axial chord of a blade or airfoil is the axial distance between the leading and trailing edges thereof. The pitch is the tangential distance between adjacent blades or airfoils mounted on the platform ring. The root, or inner diameter (ID) section of the blade or airfoil is the section thereof closest to the engine centerline, and the tip, or outer diameter (OD) section is the section thereof farthest form the engine centerline. The root radius is the radial distance from the engine centerline to the root section.
In addition, there are some normalization parameters used in normalization equations given below for use in converting normalized blade or airfoil surface coordinates for sections of the blade given in the tables below to absolute blade or airfoil coordinates to selectively scale such blades to the various sizes suited for various sized corresponding turbine engines. The blade root axial chord normalization parameter represented as Bxroot has a normalization parameter value of 1.155630 in. The blade span (form the ID section to the OD section) represented as h, as above, has a normalization parameter value of 1.905000 in. The blade root pitch represented as Pitchroot has a normalization parameter value of 1.081550 in., as determined through the platform ring radius and the number of blades selected to be mounted thereon, and the blade root radius represented as Rroot has a normalization parameter value of 10.328000 in.
Table 1, Airfoil Surface (Normalized), tabulates the normalized section cold, uncoated airfoil surface coordinates for the 16 airfoil sections indicated in
Table 2, Axial Chord Distribution, tabulates the variation in the radial direction of the axial chord of each of the cold, uncoated blade sections shown in
Table 3, Radial Stacking Distribution, tabulates the offsets for cold, uncoated blades required to accurately stack the blade airfoil sections of
Table 4, Inner Diameter Flowpath, tabulates the normalized coordinates of the cold, uncoated ring platform surface forming the inner diameter passageway limit described above with a surface profile tolerance of ±0.0500 in. including coating and manufacturing variability. The ring platform surface, or flowpath, is a three dimensional shape that begins upstream of the root section leading edge and concludes downstream of the root section trailing edge. The flowpath varies in radius from the engine centerline with both axial and tangential position, and so the coordinates describe a surface rather than a line. The axial coordinate is normalized by the root axial chord, the tangential coordinate is normalized by the root pitch, and the radial coordinate is normalized by the airfoil span. The origin (0,0,0) of the surface is aligned with the root section leading edge. The surface platform surface dips below the root section radius in some places which leads to negative radial values in the table for those locations.
The normalized coordinates for any of the sections of blade 10 shown in
where
where
R
absolute=(SpanFraction)(h)+Rroot
where
h is the airfoil span, and
Rroot is the reference root section radius relative to the engine centerline.
The ring platform surface, or inner diameter flowpath, can also be converted from normalized to absolute coordinates using the following normalization equations
Once determined in absolute space relative to the root section leading edge, the entire airfoil can then be shifted to any other location in space.
The airfoil geometry includes tolerances due to manufacturing, surface finish and coating variability of about ±0.0500 in. In addition, the airfoil as described can be rotated about its radial axis ±20° depending on the particular turbine application.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.