Duo-Propellers and Single Propellers

This application in a continuation application of U.S. application Ser. No. 17/726,468 filed Apr. 21, 2022, which claims benefit to U.S. Provisional Application No. 63/300,887, filed Jan. 19, 2022 and U.S. Provisional Application No. 63/177,645, filed Apr. 21, 2021, each of which is incorporated by reference herein in its entirety.

Contra-rotating (CR) propeller solutions, in which two propeller operate in series on co-axial counter rotating shafts, rotating in opposite directions, have been developed. CR propellers are also referred to as “duo-prop” or “coaxial contra-rotating” propellers. A single engine can drive the two propellers, transferring power through a gear assembly.

Ideally, the energy lost to the swirling flow of the forward propeller's outflow is captured by the second aft-ward propeller, which is configured to utilize that outflow to improve overall system performance. The amount of swirl energy generated by the forward propeller depends in part on the loading at the tip of the propeller blades. In conventional propellers, the amount of feasible loading is limited by the creation of vortices that can cause drag. Additionally, the fluid flow generated by the forward propeller can interfere with the operation of the aft propeller, producing limitations on the diameter of the aft propeller in relation to the forward propeller. In traditional propellers the aft prop diameter is limited to a diameter equal to or less than the forward prop to prevent impingement of tip vortices on the aft prop blades, which can be a source of cavitation, noise, and vibration.

Accordingly, there is a need for a duo-propeller having a forward propeller with improved loading and higher swirl and an aft propeller with a more optimal loading distribution to cancel the high tip swirl from the forward propeller.

A duo propeller is disclosed having a forward propeller with a more optimal loading distribution and higher swirl near the tip than a traditional propeller. The duo propeller also may have an aft propeller with a more optimal loading distribution that can cancel the high tip swirl from the forward propeller.

The rake values and skew values of the propeller blades together form a loop-shaped blade having an inlet root and an outlet root attached to a hub. The inlet root and the outlet root spaced apart on the hub such that a portion of the hub is part of the loop. This structure minimizes vortices at the blade tips.

Embodiments of the duo-propeller provide increased swirling compared to conventional propellers and enhanced ability for the aft propeller to capture the energy lost to the swirling flow of the forward propeller's outflow. Unlike a conventional propeller, the amount of feasible loading near the tip is not limited by the creation of tip vortices that can cause drag. Additionally, disclosed propeller designs reduce the interference of the fluid flow generated by the forward propeller with the efficiency of the aft propeller. Thus, standard limitations on the diameter of the aft propeller in relation to the forward propeller do not apply. This allows the aft propeller to be larger or equal in diameter to the forward propeller, although the duo-propeller would still have efficiency advantages over conventional duo-propellers if the aft propeller and forward propeller were of equal diameter.

The figures and descriptions provided herein may have been simplified to illustrate aspects that are relevant for an understanding of the described devices, systems, and methods, described herein while eliminating, for the purpose of clarity, other aspects that may be found in typical devices, systems, and methods. Those of ordinary skill may recognize that other elements or operations may be desirable or necessary to implement the devices, systems, and methods described herein. Because such elements and operations are well known in the art, and because they do not facilitate a better understanding of the present disclosure, a discussion of such elements and operations may not be provided herein. However, the present disclosure is deemed to inherently include all such elements, variations, and modifications to the described aspects that could be implemented by those of ordinary skill in the art.

depicts an illustrative CR propeller. The term “duo-propeller” may also be used in place of “CR propeller.” Propellerincludes a forward propellerand an aft propeller. Forward propelleris coaxially aligned with aft propeller. Forward propellerincludes three blades(the latter not shown in). Aft propellerincludes bladesBladesandeach form a loop. The CR propeller may include additional blades, such as four, five or six for example. Propellerrotates in an opposite direction from propeller.

The term “propeller” as used herein may include rotary blade devices that can be used to displace fluid to propel an apparatus, or which are employed in a stationary device such as, for example, a cooling or other air circulating fan, which moves fluid such as air through or around it.

depicts an illustrative bladehaving parameter sections-, with parameter sectionin the vicinity of the intake root, and parameter sectionin the vicinity of exhaust root. Each parameter section represents a set of physical properties or measurements whose values determine the characteristics of the blade. The parameter sections as a group determine the shape of bladeand its behavior. Parameter sections are equally spaced in an exemplary embodiment but may be selected at unequal intervals.serves merely to illustrate how blade parameter sections may be laid out to define blade geometry that can be applied to any type of blade disclosed herein. Parameter sections represent the shape and orientation of bladeat a particular place along the blade. A smooth transition is formed between parameter sections to create a blade. As used herein “orientation” may include location. In the illustrative embodiment in, blade sections-are planar sections disposed along an irregular helical median line. “Irregular helix” is used herein to mean varying from a mathematical helix-defining formula or as a spiral in 3-D space wherein the angle between the tangent line at any point on the spiral and the propeller axis is not constant. The blade may have an irregular, non-helical median line at least in part, or the median line may be an irregular helix throughout.

Althoughblade sections are shown in, more or fewer sections can be used to define a blade. Additionally, sections may exist within or partially within the hub that are not shown or fully shown. Blades may be defined by planar or cylindrical parameter sections.

Parameter sections-are defined, for example, by orientation variables, such as roll angle and vertical angle (alpha), and may include location variables; and shape variables, such as chord length, thickness, and camber. Additional illustrative orientation or location variable include rake, skew angle and radius. Some or more of the variables may change throughout the blade or a blade portion and some may be constant throughout. Orientation variables may be measured with respect to an X-Y-Z coordinate system. The X-Y-Z coordinate system has the origin at the shaft centerline and a generating line normal to the hub or shaftor hub axis, such as hub axisshown in. The X-Axis is along hub axis, positive downstream. The Y-Axis is up along the generating line and the Z-Axis is positive to port for a right handed propeller. A left-handed propeller is created by switching the Z-Axis and making a left hand coordinate system.

Parameter sections may be located by their chord (nose-to-tail) midpoint, such as by using radius, rake and skew. Parameter sections may be oriented using the angles phi (skew), psi (roll) and alpha (pitch), as will be described further below.

is a schematic of a propeller blade to illustrate the inlet portion, tip portion and outlet portion of a propeller blade. The tip portion is the darker area connecting the inlet portion to the outlet portion. This illustration can be applied to any of the blades disclosed herein. In an illustrative embodiment of a propeller, the inlet portion extends from an inlet root to where the blade reference line is 88% of the blade outer radius and increasing. The outlet portion extends from where the blade reference line is 88% of the blade outer radius and decreasing to the outlet root. The tip is the portion between the inlet portion and the outlet portion. The blade reference line is the curve connecting all the parameter section mid-chord points. In a further illustrative embodiment, each of the inlet portion and the outlet portion extend from their respective root to where the blade reference line is in the range of 75% to 100% of the blade outer radius and increasing. The tip portion in the remaining portion between the inlet and outlet portions.

depicts an illustrative blade parameter section geometry by reference to a cross-sectional profile of a blade. The illustration is merely to provide definitions and can be applied to any of the blade or propeller embodiments described herein. An illustrative parameter section is in the form of an asymmetrical airfoil. The airfoil is bounded by a curved blade surface lineand a generally flat blade surface line, with a rounded noseat the leading edgeof the parameter section and a pointed or less rounded tailat the trailing edgeof parameter section. Parameter sections may also be in the shape of a symmetrical airfoil. Additional parameter section shapes include, for example, a shape having parallel blade surface lines,. Blade surface lines,may also be linear and at an angle to one another. The nose and tail edges may both be rounded, both be flat (perpendicular to one or both blade surface lines,) or one of either the nose or tail may be rounded and the other of the two flat. A blade formed of a sheet material, for example, would generally exhibit parallel blade surface lines,. In an illustrative example of a blade formed of a sheet, the leading edge of the blade is rounded and the trailing edge is flat or less rounded, though both intake and trailing edges could be rounded.

Illustrative shape variables for parameter sections are defined as follows;

Illustrative orientation variables include:

Illustrative rake measurements are shown infor various parameter sections.generally describe various parameters of a propeller blade and can be applied to any of the blade or propeller embodiments described herein. Each ofshow coordinates X, Y and Z, wherein the X-axis is coincident with the propeller rotational axis, and the Y-axis and Z-axis are perpendicular to the X-axis, and the three axes are mutually perpendicular. Parameters are measured from the origin of the coordinate system. In an illustrative embodiment, the zero point of the coordinate system is along the propeller rotational axis, and is closer to the intake root than the exhaust root. Illustratively, values along the X-axis toward the intake root are negative and toward the exhaust root are positive. In general, a coordinate system can be located as desired and all parameters or geometry are measured from the origin of the selected coordinate system.

depict rake for parameter sections,on the intake portionof blade. Parameter sectioninis toward tip portionof blade. Parameter sectioninis toward intake root. Rake is measured along the propeller rotational axis or along a line parallel to the rotational axis. In the illustrative examples of, rake is the distance from point A at X equals zero to the X coordinate value of point B, wherein point B is at the midpointof the chord of parameter sections,. The X-coordinate value of point B is represented by Bx in. Chords of parameter sections shown inare defined by end points,.

depict rake for parameter sections,on the tip portionof blade. Parameter sectioninis at a first position in tip portionof bladewherein the roll value (described further below) is greater than zero and less than 90 degrees. Parameter sectioninis at a second position in tip portionwhere the roll value is equal to or greater than 90 degrees. In the illustrative examples of, Rake is the distance from point A at X equals zero to the X coordinate value, B.sub.x, of point B, wherein point B is at the midpointof the chord of parameter sections,.depict Rake for parameter sections,on the exhaust portionof blade. Parameter sectioninis toward tip portionof blade. Parameter sectionis toward exhaust root. In the illustrative examples of, Rake is the distance from point A at X equals zero to the X coordinate value of point B, wherein point B is at the midpointof the chord of parameter sections,.

schematically describe rake angle, which is difference than the linear rake measurements described above. Rake is the axial sweep of the blade in the direction of the axis of rotation. Rake value increases as the angle between the blade axis of rotationand the median rake line of the blade decreases. In practice, the actual rake line is typically a non-linear curve. Rake is the determining factor in the axial blade-to-blade separation.

As shown in, a negative rake would be a forward angle relative to the blade root position, and a positive rake would be an aft-wards angle relative to the blade root position.

The disclosed novel propeller has blades with unique rake values for the inlet and outlet sections, which are independently configured. The dot-dash lines shown inindicate there exists a “collective rake” for any given design. A propeller can be described as lower rake () and higher rake ().

Rake angle can be calculated by:

In a further illustrative embodiment, rake is calculated by:

A blade section or parameter section is the airfoil section at each spanwise station that is used to build up the blade, not a section cut of a 3D blade. In an illustrative embodiment the sections are based on standard sections developed by National Advisory Committee for Aeronautics (NACA), National Aeronautics and Space Administration's (NASA's) predecessor. The standard sections are then scaled to get the absolute Thickness and Camber we want at each station.

The geometry (particularly rake and skew) could be defined from either root. In an illustrative embodiment, the geometry is defined from the inlet. Traditionally, propeller geometry is based on (or near) the root and rake is determined from this point and the rake Angle is determined from this point. To the contrary, for embodiments of the propellers disclosed herein, the geometry is based on (or near) the inlet root and the rake angle is determined from the average of the inlet root and/or the outlet root.

depict bladeviewed along the blade rotational axis X.identify representative parameter section radii and skew angle.generally can be applied to any of the blade or propeller embodiments described herein.depicts the radius of parameter sectionin the intake portionof blade.shows the radius of parameter section, a parameter section in intake portionof bladefurther from intake rootthan parameter section.depict radii for parameter sectionand, respectively, wherein parameter section,are in tip portion.depict radii for exhaust parameter sectionand, respectively, both within exhaust portion. The position of parameter sections,,,,andas being in intake portion, tip portion, or exhaust portionare provided only for ease of discussion. The actual parameter values and resulting fluid flow may define the positions of the sections otherwise.

show skew angle of parameter sections,,,,,. Skew angle is the projected angle from a line through midpointof chordto the generating line, in this illustrative embodiment the Y-axis looking along hub axis(X-axis).

, in addition to depicting skew angle and radius, depict parameter section vertical angle, alpha, labeled on each of.generally describe various parameters of a propeller blade and can be applied to any of the blade or propeller embodiments described herein. Vertical angle may also be referred to as “lift angle.” Alpha is the angle that the parameter section is rotated relative to a line perpendicular to the skew line, which is identified in. The aforementioned skew line refers to the line together with the zero skew line that forms the skew angle. Depending on the value of Alpha, the nose of the parameter section will either be “lifted” or will “droop” from a line perpendicular to the skew line that forms the skew angle with respect to the zero skew line, wherein the zero skew line is coincident with the Y-axis of the coordinate system identified on.

Various illustrative embodiments will be described by combinations of characteristics. The disclosed propeller includes different combinations of the characteristics, equivalents of the elements and may also include embodiments wherein not all characteristics are included.

provide a schematic representation of pitch angle for various parameter sections. Pitch angle varies throughout the blade with the largest values occurring at the intake and exhaust roots.

Embodiments of single propellers will be described that can be used individually or in combination to form duo-propellers.

depict a propeller, that will be referred to as a “Type 1” propeller.depict an isometric view, and a view from the forward end, respectively.depict a propeller, that will be referred to as a “Type 2” propeller.depict an isometric view, and a view from the forward end, respectively.

depict illustrative combinations of propellers to form a CR propeller, such as CR propeller. Each of the CR propellers have the parts identified in generic CR propellershown in. These include at least in part, forward propeller, aft propeller, bladesbladestrailing edge, leading edge, and propeller axis. CR propellermay be formed from the combination of a Type 1 propellerand Type 2 propeller, with the Type 1 propellerpositioned aft of the Type 2 propeller, as shown in. The forward propeller has high rake (R2) and the aft propeller has a minimum rake R0.shows another illustrative CR propeller, in which a Type 1 propelleris forward of a Type 2 propeller. Both the forward propeller and aft propeller ofhave a high rake R2. Alternatively, CR propellermay be formed from the combination of two Type 2 propellers, such as shown in, wherein both the aft and forward propellers have a high rake R2, or two Type 1 propellers, such as shown in, where the forward propeller has a high rake R2, and the aft propeller has a low rake of R0. A Type 3 blade form is also feasible but not shown. Not shown but implied are all R0, R1, & R2 variants of T1 and T2 styles, and all forward and aft position permutations. T3 blade form is also feasible.

depict Type 1, Type 2 and Type 3, propellers, respectively. Lines through the roots of each propeller blade show the direction of the wakes created by the blades.

As depicted in, a blade of the Type 1 propellerhas the inlet root sectionpositioned axially forward and rotationally forward of the outlet root section. The paths of the Type 1 inlet blade wakeand outlet blade wakeare substantially parallel and not prone to crossing one another. The trailing wake is particularly important for this type of propeller because it has a strong influence on the water flowing over the outlet portion of the blade. The outlet portion is designed to operate in, or very close to, the wake sheet coming off the inlet trailing edge. Placement of the outlet portion with respect to the wake sheet coming off the inlet trailing edge is selected to optimize the propeller's performance to the extent that position can be balanced with other design requirements. In an illustrative embodiment, an application-specific propeller is made by selecting the type of propeller, such as Type 1, Type 2 or Type 3. The selected type determines where the inlet and outlet roots are positioned on the hub relative to one another. For example, for a Type 1 propeller, the outlet root will be close to the extended chord line of the inlet root, such as shown in. In a further example, for a Type 3 propeller (as will be described below) the outlet root will be near the same axial location as the inlet root and will not be near the extended chord line, as shown in.

As shown in, Type 2 propellerhas the inlet section of the blade root sectiondisposed upon hubin about the same axial position as the outlet root sectionand is rotationally behind the outlet root section. Like with the Type 1 propeller, for the Type 2 propeller the paths of the inlet blade wakeand outlet blade wakeblade wake are substantially parallel and not prone to crossing one another. The distinction between the Type 1 and Type 2 propeller is related to the axial position of blade roots. The trailing wake is less important for this propeller type because the outlet section does not operate near the inlet section trailing wake. For the Type 2 propellerthe design of the tip is prioritized over the placement of the outlet portion with respect to the wake sheet coming off the inlet trailing edge.

In conventional CR propellers, the forward propeller is larger in diameter and has a different number of blades than the aft. For propellers disclosed herein, the forward and aft propellers may have the same diameter, different diameters, the same number of blades, or different numbers of blades, or a combination thereof. An illustrative range of diameter differences includes, the aft propeller having a diameter in the range of 80%-100% of the forward propeller. In a further illustrative range, the aft propeller has a diameter in the range of 100%-130% of the forward propeller. When accounting for non-cylindrical hubs an illustrative range of diameter differences includes, the aft propeller having a diameter in the range of 33%-100% of the forward propeller. In a further illustrative range, the aft propeller has a diameter in the range of 100%-175% of the forward propeller.

A key parameter to optimize the propeller's performance is the blade-to-blade distance D between the propellers. This is measured parallel to the hub axis from the trailing edgeof the forward blade to the leading edgeof the aft blade. Blades on the aft propeller must clear the blades on the forward propeller as they rotate in opposite directions. Additionally, the axial blade-to-blade distance D, together with other parameters affects efficiency. In a particular embodiment, optimally the blade-to-blade distance is as small as possible, with the limiting factor being a minimum allowance to prevent collision.

Another general propeller parameter of importance is the axial length and space required for the blade and hub to fit the engine configuration and boat hull architecture. Axial Length and space required for a propeller is constrained by aftward placement of the rudder, and forward proximity to the hull and shaft bearings. Additionally, the total length of the system may beconstrained by the position and length of the anti-ventilation plate.

Other key parameters include rake and skew, which are selected for each spanwise portion of the blade to create the inventive contra-rotating propeller.

The disclosed propeller types are less constrained than standard propellers in a contra-rotating system. For example, the downstream wake system of a three bladed loop propeller behaves like the weaker downstream wake system of a six-bladed propeller, which typically is favorable because the after propeller blades experience smaller wake extremes (6 weaker vs 3 stronger).

The disclosed propellers have improved efficiency because the tip portions reduce the required torque. The tip also changes the water flow over the inner parts of the blade so that the inner parts are more efficient by producing more thrust and or less torque.

Propeller, and combinations of propellers,are all shown with three blades on each of the forward propeller and aft propeller. As noted above, the number of blades can be greater than three. Additionally, the number of blades on the aft propeller may be different from on the forward propeller. For example, the number of blades on the forward propeller may be selected from 2, 3, 4, 5, 6 and 7 and the number of blades on the aft propeller may be selected from 2, 3, 4, 5, 6 and 7, allowing for any combination between the number of blades on the forward propeller and the number of blades on the aft propeller. The inventive contra-rotating propeller may include any combination of blade or propeller styles, for example, Type 1 propellersor Type 2 propellers, various number of blades and various combination of diameters.

The inventive CR propeller has unique parameters, such as:

In illustrative embodiments of the duo-propeller, the locations and strength of the blade trailing wake are selected to achieve the desired forces on the propeller.