Determining test-bench box aerodynamics impact on the force from the gas turbine engine thrust by layout changing of the inlet lemniscate mouth piece

DOI: 10.34759/vst-2021-4-163-179

Аuthors

Klinskii B. M.

e-mail: bmklinskiy@ciam.ru

Abstract

Parameters measurement accuracy while gas turbine engine (GTE) tests is incurring direct impact on the tests quality and engine parameters setting-up during its pilot and serial production. Considerable attention while testing is being paid to the accuracy of the engine main output operating parameters determining such as thrust and specific fuel consumption, since these parameters directly affect the aircraft flight characteristics. However, accuracy of these parameters actual values determining while the GTE bench testing is being affected by many factors, the main of which are the aerodynamic characteristics of the test-bench box. Determining the test-bench aerodynamic characteristics impact on the engine thrust is being performed in accordance with the Industry Standard OST 101021-93 «Test-benches for aircraft gas turbine engines. General requirements» and according to the «Aerodynamic force at gas turbine engines tests on the ground-based closed test-benches» measuring technique adduced in the OST 1 02781-2004 Standard. However, this technique is applicable only to the turbojet and turbofan engines with common nozzle on the supercritical operation mode at π*_nozzle ≥ π*_{nozzle crit}.

The purpose of this work consists in developing a technique for the aerodynamic force value determining as a correction to the force from the engine thrust. This value is being measured with the force measuring system in the (closed) box of the test-bench based on comparing the bench-testing results of the GTE with a large degree of double-flow with separated circuits under condition of H = 0 and M = 0 at two layouts of the inlet lemniscate device. This technique proposes determining the reduced value of the aerodynamic force determining for the selected GTE type on the steady-state modes of the engine operation at the constant value of the reduced rotor rotation frequency n_r cor = const in the (closed) box of the test-bench in two options. The first option supposes the layout with mechanically connected lemniscate (the reduced thrust of the test-bench R_eng.cor is being determined with no account for the values of the input impulse ΔR_inlet and aerodynamic drag ΔR_windage), employed while acceptance bench-test. The second option employs the layout with the lemniscate mechanically disconnected by the labyrinth seal. The reduced thrust of the test-bench R_0eng.corr is being determined herewith with account for both the input impulse in the section of the labyrinth seal of the inlet test-bench device and external aerodynamic drag ΔR_windage with connected pipeline at the inlet, applied while the test-bench box calibration, as the difference between the thrust values ΔR_{air_force cor} = R_0eng.corr – R_eng.corr. The article presents the technique for test-bench thrust reduction to normal conditions H = 0 and M = 0 of GTE with large double-flow degree with split circuits at subcritical modes of the jet nozzles. This is being done at the total pressure loss σ_in in the inlet device difference from 1.0, as well as total pressure at the inlet P_in^*, damped temperature T_in^* and the moisture content d difference from the standard values.

The aerodynamic force value (ΔR_AF) determining error estimation according to the technique being suggested was performed in the article.

The article estimates the error in determining the value of the aerodynamic force according to the proposed method.

The article demonstrates the possibility of employing, if necessary, a certified high-altitude test-bench for the aerodynamically non-certified box of the test-bench to determine the aerodynamic force reduced value (ΔR_{air.force.cor}) for the selected turbofan type. The demonstration is based on the example of satisfactory comparison of the experimental values of the reduced test-bench thrust of the turbofan of large double-flow degree with separated circuits in the mode n_fan.cor = const in the certified (closed) box of the test-bench. The experiment was conducted in both layout with mechanical coupling by the input lemniscate, and in thermal pressure chamber of the certified high-altitude test-bench with mechanically detached lamniscate under conditions of H = 0 and M = 0.

The technique for the aerodynamic force determining as a correction to the force from the engine thrust, recounted in the article, may be applied for aerodynamic calibration of the non-certified closed box of the text-bench to account for the value of aerodynamic force. This can be done while both development tests of the pilot item and acceptance tests of a stock-produced turbofan of a large double-flow degree with separate circuits.

Keywords:

double-flow turbofan engine, test-bench box, inlet lemniscate mouth piece, engine thrust, force from engine thrust, air mass flow rate, rotor speed, aerodynamic force, aerodynamic drag coefficient

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