The project is aimed on enhancing the aerodynamic performance of novel engine air intake concepts for helicopters by shape optimization.
Comprehensive wind tunnel tests are performed on a full-scale model of a helicopter fuselage section comprising engine cowling and air intake flow passages. The main effort is on two wind tunnel campaigns to analyse in detail the aerodynamic characteristics of three baseline air intake configurations and several design variants. The design modifications concentrate on flow guiding elements like fillets, vanes, spoilers and scoops. The measurements include total pressure and three component velocity fields at the aerodynamic interface plane (AIP) to quantify total pressure losses and inflow distortions. For optimum engine performance, such values have to be minimized by geometry adaptation. Setting up an extensive data base, steady and unsteady surface pressures on cowling and air intake regions are recorded simultaneously to the AIP measurements and correlated with field measurements of mean and fluctuating velocities documenting the incoming flow.
A new wind tunnel model consisting of the extended fuselage cowling part and all air intake components and flow passages is designed, manufactured and instrumented to carry out the experiments. The model is of high modularity to easily exchange the various air intake components. Data analysis and evaluation will provide highly required guidelines for helicopter air intake design.
The European Union has launched the CleanSky initiative together with the European aerospace industry aimed at a reduction of emissions and fuel burn. The engine installation plays an important role to foster fuel-efficient engine operation and decrease emissions. The sub-project GRC2 of the Green Rotorcraft ITD (Integrated Technology Demonstrator) aims at improving the aerodynamic characteristics of helicopter and tiltrotor aircraft fuselages and engine installation. In this context, the investigation and optimization of engine installation plays an important role to ensure and foster fuel-efficient engine operation. To cover a wide range of the future helicopter fleet, weight classes from light to heavy are treated within GRC2. Numerical optimization of several configurations is carried out by means of Computational Fluid Dynamics (CFD) and expected benefits of identified solutions are assessed through wind tunnel tests.
Comprehensive wind tunnel tests were performed on a full-scale model of a helicopter fuselage section at the Institute of Aerodynamics and Fluid Mechanics of the Technische Universität München (TUM-AER). For that purpose, a new wind tunnel model of a lightweight twin-engine helicopter comprising a fuselage cowling part, all air intake components as well as flow passages was designed, manufactured and instrumented.
The model features a high degree of modularity for easy comparison of various air intake components. In two wind tunnel campaigns aerodynamic characteristics of three baseline engine air intake configurations and several design variants were analysed in detail. The design modifications concentrate on flow guiding elements like fillets, vanes, spoilers and scoops. With a five-hole pressure probing system, flow field measurements were conducted at the aerodynamic interface plane (AIP). Additionally, steady and unsteady surface pressures on cowling and air intake regions are recorded. The incoming flow was investigated by field measurements of mean and fluctuating velocities. Data analysis and evaluation provided a valuable database and guidelines for helicopter air intake design.
The geometric variations tested in the first W/T campaign have been developed and provided by the GRC Consortium. In this baseline campaign 3 different intake variants have been tested according to a measurement matrix which was specified together with Airbus Helicopters Germany.
Baseline variant 1 was developed as a static inlet. Limitations on the inlet area cross section are imposed by engine plenum sizes. The second baseline variant of the intake was designed as a “semi-dynamic” intake. In contrast to the baseline variant 1 it features a ramp as part of the intake for recovery of dynamic pressure. It has been optimized for level flight conditions. The third baseline air intake comprises the same main geometry of baseline intake 2. Furthermore, it features a scoop. The scoop defines a section perpendicular to the main flow direction the incoming air has to pass to enter the engine air intake. It guides the free stream flow into the intake and recovers more dynamic into static pressure from the inlet section up to the compressor. Two different engine plenum chambers were tested. The baseline plenum chamber 2 features an overall rounded shape compared to plenum chamber 1. The first intake variant was tested with the first plenum chamber. Both intakes two and three were tested with plenum chamber two. For the first two combinations of baseline intakes and plenum chamber variations with and without an outer and inner foreign object damage grid were investigated.
Prior to the wind tunnel campaign preliminary testing of the suction system, the 5-hole probes and their traversing system was conducted at TUM. The production measurements of the first wind tunnel campaign were performed at the W/T A facility of TUM due date.
The first campaign was meant to provide a database of surface pressures and 3 component velocity data as well as total pressure data at the AIP. As a part of work reporting period 2 a detailed analysis of the data was carried out in order to identify optimization potential for further improvement of the baseline geometries using retrofit solutions.
With respect to the 3 different intake variants tested in the first measurement campaign, the baseline variant 2 (BSL 2) has been chosen as basis for the optimization.
Based on the detailed analyses of the results of the 1st wind tunnel measurement campaign, retrofit variants, namely a rear spoiler (small scoop), inlet guide vane and a combination of both, were investigated in the 2nd wind tunnel measurement campaign.
First, four different rear spoilers were tested in combination with the baseline 2 intake to assess the best combination of the height and length of the rear spoiler. In general, an increase of the height increases the cross section at the intake, thus increasing the ram effect. A decrease of the spoiler length leads to a bigger leading-edge radius as well as to a shorter distance for which the flow must trail on the upper side of the spoiler in the hovering condition.
Both measures led to the desired effect to combine the beneficial operating conditions of baseline intake 2 and 3.