NON-LINEAR EFFECTS OF AIRFOIL FORCE DATA ON DESIGN PERFORMANCE OF A LOW-REYNOLDS NUMBER PROPELLER

Umunna J Reuben,Miyamoto Shohei,Koju Hiraki

doi:10.29121/granthaalayah.v6.i8.2018.1450

Umunna J Reuben, Miyamoto Shohei + Show 1 more

Open Access

https://doi.org/10.29121/granthaalayah.v6.i8.2018.1450

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Abstract

Over the last three decades and a half, there has been huge effort to develop high performance propellers suitable for flight in the rarefied Mars atmosphere. This paper describes work undertaken in validating vortex theory in the design of a 2-bladed heavily loaded propeller with a solidity of ≈0.25 and chord based Reynolds number of ≈60k (calculated at 75% radius) at design point. The design was based on minimum induced propeller losses and lifting line theory. 2D-airfoil experiment data of SD7037 collected at Reynolds number of 60k was used for the entire blade design. At design advance ratio, more than 50% of the entire blade radius operated between 40k – 60k Reynolds numbers. A design goal of the propeller was to minimize variation in Reynolds number from hub to tip radius. Wind tunnel tests carried out at Kyushu Institute of Technology were performed in two (2) ways: constant angular velocity and changing airflow velocity over the propeller, and constant airflow velocity and changing propeller angular velocity. The fabricated propeller showed good agreement in efficiency for both test cases. However, considerable discrepancy was observed between theory and experiment in thrust and power. Investigation showed that non-linearity associated with airfoil aerodynamic data not captured by linearization result in a less representative modeling of the airfoil force coefficient and consequently, discrepancy in propeller performance between theory and experiment.

Highlights

There has been considerable interest in Low-Reynolds flights driven by efforts to develop micro air bots for various applications: achieving flights within the stratosphere and in the rarefied Mars atmosphere
The constant angular velocity test method allowed a greater range of RPM sweep, the propeller performance was assessed from a lower and much wider advance ratio range
Blade element momentum theory was used in the design of a 2-bladed propeller with solidity of 0.24 and chord based Reynolds number of ≈60k calculated at 75% radius and advance ratio of

Summary

Introduction

There has been considerable interest in Low-Reynolds flights driven by efforts to develop micro air bots for various applications: achieving flights within the stratosphere and in the rarefied Mars atmosphere. For a Mars flight, extremely low fluid inertia and speed of sound limits the propeller tip speeds adding to the design complexity. Other design consideration includes; compactness of the design to ensure fit into aerosols from where it would be deployed for operation on entry into Mars atmosphere. The propeller design presented in this work was not designed to meet the propulsion demands of any specific air vehicle but rather the goal was to validate the application of lifting line theory and minimum induced losses in the design of high solidity, low Reynolds number operating propellers. The implementation of graded momentum formulation in Xrotor notes that the momentum formulation is unsuitable for advance ratios greater than 0.5 [4]

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