The results of a numerical simulation of the time-averaged inviscid flow field through the blade rows of a multiblade row turboprop configuration are presented. The governing equations are outlined along with a discussion of the solution procedure and coding strategy. Numerical results obtained from a simulation of the flow field through a modern high-speed turboprop will be shown.

/pdf/a-numerical-simulation-of-the-inviscid-flow-through-a-4s395se3em.pdf

A Numerical Simulation of the Inviscid Flow Through a Counterrotating Propeller

A new integral equation for propeller steady aerodynamic analysis is presented that generalizes wing kernel function methods to include effects of rotation and multiple blades. The kernel of the integral equation is valid in a single form for the case, typical of propfans (advanced technology, many bladed propellers which operate at high cruise Mach number), where the blade section relative speeds are subsonic at the roots and supersonic at the tips. Within the restrictions of linearized theory, effects of blade interference, sweep, three dimensionality, and compressibility are rigorously accounted for. Behavior of the kernel is studied and compared with well-known results from wing and propeller wake theories. Methods for inverting the integral equation to compute lift distribution and for determining vortex (or induced) drag are adapted from wing theory. Computed efficiency, power, and spanwise power distribution are in excellent agreement with data for a propfan model with swept blades tested at 0.8 cruise Mach number in a NASA wind tunnel.

Compressible lifting surface theory for propeller performance calculation

Advanced high-speed propellers offer large performance improvements for aircraft that cruise in the Mach 0.7 to 0.8 speed regime. At these speeds, studies indicate that there is a 15 to near 40 percent block fuel savings and associated operating cost benefits for advanced turboprops compared to equivalent technology turbofan powered aircraft. Recent wind tunnel results for five eight to ten blade advanced models are compared with analytical predictions. Test results show that blade sweep was important in achieving net efficiencies near 80 percent at Mach 0.8 and reducing nearfield cruise noise by about 6 dB. Lifting line and lifting surface aerodynamic analysis codes are under development and some results are compared with propeller force and probe data. Also, analytical predictions are compared with some initial laser velocimeter measurements of the flow field velocities of an eightbladed 45 swept propeller. Experimental aeroelastic results indicate that cascade effects and blade sweep strongly affect propeller aeroelastic characteristics. Comparisons of propeller near-field noise data with linear acoustic theory indicate that the theory adequately predicts near-field noise for subsonic tip speeds but overpredicts the noise for supersonic tip speeds.

Summary of recent NASA propeller research

This paper offers an analytical formulation of the two errors embodied in the momentum theory. The first one originates from the use of the differential form of the axial momentum equation and the second one originates from the linearization of the tangential velocity terms. Both errors are evaluated by comparing the axial velocity at the disk as predicted by the momentum theories with the one obtained thorough a semianalytical actuator disk method based on the exact solution of the flow. Several cases characterized by different values of the thrust and advance coefficient are analyzed, and the range of validity of the momentum theories is discussed in depth.

Analysis and Evaluation of the Momentum Theory Errors as Applied to Propellers

A technique for the simulation of unsteady flows in and around complex rotating machinery is presented. Additional domain decomposition mechanisms are introduced which extend the range of applicability of software developed for the time-accurate simulation of rotating machinery flowfields. The flow models uses the unsteady 3D Euler equations, discretized as a finite-volume method, utilizing a high-resolution approximate Riemann solver for cell interface flux definitions. Multiblock domain decomposition is used to partition the field radially, axially, as well as circumferentially into an ordered arrangement of blocks which exhibit varying degrees of similarity. A general high-order numerical scheme is applied to satisfy the geometric conservation law. Two configurations are presented - ducted single rotation prop-fan and a rotor-deswirl vane combination which form a single stage fan. Comparisons are made to other numerical solutions for these geometries and to available experimental data.

Unsteady flowfield simulation of ducted prop-fan configurations

To overcome the limitations of classical propeller theory, a computer program, NASPROP-E, was developed which solves for the flow field surrounding a multibladed propeller and axisymmetric nacelle combination using a finite difference method. The governing equations are the three dimensional unsteady Euler equations written in a cylindrical coordinate system. They are marched in time until a steady state solution is obtained. The Euler equations require no special treatment to model the blade work vorticity. The equations are solved using an implicit approximate factorization method. Numerical results are presented which have greatly increased the understanding of high speed propeller flow fields. Numerical results for swirl angle downstream of the propeller and propeller power coefficient are higher than experimental results. The radial variation of coefficient are higher than experimental results. The radial variation of swirl angle, however, is in reasonable agreement with the experimental results. The predicted variation of power coefficient with blade angle agrees very well with data.

https://ntrs.nasa.gov/api/citations/19830011439/downloads/19830011439.pdf

Prediction of high speed propeller flow fields using a three-dimensional Euler analysis

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Prediction of high speed propeller flow fields using a three-dimensional Euler analysis