Thermal management of hydraulic circuits is critical to earning an airworthiness certificate, and aircraft manufacturers must assess the circuit’s integration in the aircraft along with its thermal impact without exceeding maximum defined temperatures. Further, it must be certified there is a well-designed and working hydraulic circuit that can support proper flight command functioning even in case of leakage, pump failure, etc.
Time and cost
Getting certified is a long process, so engineers must consider development time. The earlier a manufacturer can obtain certification, the faster it can get to market and the more competitive it can be. Also to be considered is the cost of prototypes incurred by test campaigns.
A manufacturer cannot bypass the prototype test phase, whether it is for the system or once the system is integrated into the aircraft. Nevertheless, there are means to assess and define the best system architectures early in the development cycle, as well as the thermal management of the full system based on the architecture definition analysis. Employing system simulation enables manufacturers to predict and evaluate strategies to maintain the heat balance of an aircraft program.
Airbus Helicopters’ Benoit Genot, hydraulic and flight control engineer, and Jean-Baptiste Lopez-Velasco, thermal management expert, and their teams decided to opt for Siemens’ Simcenter Amesim when they were developing the Airbus Helicopters H160, a six-ton, new-generation, medium-sized rotorcraft. They used the software to accurately predict and verify the thermal-hydraulic system’s performance from early stage system sizing to fully integrated design. Their objective was to provide power to the main actuators installed on the helicopter while designing the hydraulic circuit. This is done under specific conditions, such as not exceeding temperature qualifications in hot conditions that can reach 50°C (122°F) outside air temperature.
“Our first objective was to design a rough architecture of a hydraulic circuit,” Genot says. “Each hydraulic power supply unit is composed of a tank, sensors (temperature/pressure/fluid level), pumps, and an emergency pump in case a main pump fails. The whole circuit is linked to the main rotor actuators and the tail rotor actuator. For that we use Simcenter Amesim and its supercomponent capabilities to design some of our components.”
It is crucial to understand the thermal influence of the hydraulic system on other helicopter parts. Once integrated into the helicopter, around 90% of the hydraulic circuit covers the upper deck and main gearbox compartment, the area Lopez-Velasco analyzes.
“Based on the first scheme of the hydraulic system – modeled according to normal and failure cases conditions – we can start the thermal modeling using Simcenter Amesim,” Lopez-Velasco says. “One of the questions the software helps us clarify is whether it is required to cool the fluid – in that case we need to use a heat exchanger. Then, during the development, there are several loops of calculation to refine the model.”
Saving time on test campaigns
“Tests remain mandatory for modeling construction and validation,” Lopez-Velasco adds. “Using Simcenter Amesim for system simulation enables us to anticipate model architecture so we can save time on the test campaigns because our model is already fine-tuned.”
During test campaigns, Airbus Helicopters’ teams test the system in normal and failure modes. Measurements are done at different levels to assess oil temperature, ambient temperature, velocities, pressures, and flowrate. In addition to comparing the test and simulation, the parameters of the simulation model are refined based on the test results. This makes the model as true as possible to the physical version of the product.
In this case, Genot and Lopez-Velasco reached an accurate result because the difference between the Simcenter Amesim modeling and the test bench results only varied by ±5°C while the aircraft was stationary.
“Modeling with Simcenter Amesim permits us to anticipate the design and architecture freeze of the hydraulics systems (routing, tank, heat exchanger) to secure the development cost and planning,” Genot says.
In the future, Genot and Lopez-Velasco plan to study different weather cases, work on transient calculations (not only for stationary analyses), and integrate a real-time platform with Simcenter Amesim.